Electrical Engineering - Looking for a UPS Design That Doesn't Overheat Batteries

Author

Looking for a UPS Design That Doesn't Overheat Batteries

Will

2006-06-01, 2:21 am

Our company has had a long-standing problem where UPS batteries will at
various points in their lifetime suddenly overheat, sometimes
catastrophically to the point where the battery casing starts to melt and
you can actually smell the gases from the battery leaking. So far we have
been lucky to catch such thermal events with temperature sensors but it has
always been a goal of mine to better understand why this happens, and to
find some UPS system where it can be avoided entirely. To date, we have
seen these problems with APC Symmetra tower, Symmetra rackmount, and
SmartUPS.

After working with an electrician, I have a theory about why this is
happening, and if correct, the theory suggests a different design for UPS
systems that would avoid the problem. I am hoping some manufacturer has
already implemented this idea and someone can refer me to their products.

On all of the UPS systems we use generic "brick" batteries are joined
together in a series, then the leads from the ends of these battery chains
are connected to the UPS. The problem is that batteries rarely fail all
together. If a 12V battery should be considered discharged and not useful
at around 10V, and you have two 12V batteries joined in series, what happens
when one of the batteries maintains a full charge at 12V but the other
battery in the series starts to lose its ability to hold charge and slips
below some critical level? From the point of view of the UPS, it
doesn't see anything about the state of individual batteries. The UPS only
sees that the total voltage of the two 12V batteries in series has fallen
from 24V to 22V.

Maybe an electrical engineer can step in here and explain what is happening,
but my pure guess is that to maintain the same power output, an increased
amount of current probably has to flow through the batteries. That
creates problems with heating for the "good" battery, which is still
measuring 12V. Now that 12V is receiving too much current, overcharges,
overheats, and at some point the casing of the battery starts to melt. I
haven't done enough experimentation to determine if it is the good battery
or bad battery that is overheating. To be honest, in such situations I
have often seen evidence that both batteries start to melt. Perhaps this
is nothing more than one battery being in physical proximity to the
overheating battery and therefore gaining heat from its physical contact.
The only thing that is common to all cases is that one of the two batteries
has discharged and should have been replaced before the overheating event
took place.

Regardless of the actual mechanism for the overheating we are observing, it
seems to me that the obvious solution is to design UPS systems to physically
connect to each 12V battery individually. Forget connecting multiple
batteries in series, at least don't do that at the battery itself. By
connecting to and monitoring individual batteries, now the UPS can see when
an individual battery falls below some critical voltage threshold and put it
into a special recharge state (not put any load on it). If the battery
fails to recharge, the UPS can declare the battery defective and can signal
the condition by an LED on the battery's compartment. If there is a
network attached monitoring system, the UPS can send an e-mail.

Aside from increasing safety and utility of the monitoring system, such a
design would allow much easier re-use of off-the-shelf batteries, improving
ease-of-use in making battery changes and lowering cost. While I realize
that APC in particular has no desire to make anything regarding batteries
non proprietary, maybe some other vendor has a UPS design that puts a direct
monitoring circuit on each individual 12V brick battery, thus avoiding the
overheating problem I have described?

Any information on why this overheating takes place, how to avoid it, and
any referrals to third party UPS products that employ a more robust design
are appreciated.

--
Will

Mike

2006-06-01, 3:21 am

Seen this before, most UPS dont have individual temp sensors
on each battery and/or dont have them in the right place and/or
maybe more than one per battery is needed. I have a solution I
have been working on with a battery manufacturer which I cant
discuss for commercial reasons but I can say we havent pursued
it much because the issue hasnt been so major - its just been
'occasional' and didnt warrant a whole new topology, this might
have changed, so thanks for your report. There are intermediate
fixes you can do for any UPS if you can open it up, so I'd
suggest that route first, esp for UPS that are mostly unattended.
I heard of one situation where an office was left overnight with
the UPS functioning online and the owner entered the premises
in the morning to find the room was quite warm and a bad acrid
smell throughout. Turned out the batteries had been overcharged
because one or more cells had shorted and the UPS wasnt the
smart one they said it was <sigh>

Cheers

--
Regards
Mike
* GMC/VL Commodore, Calais VL Turbo FuseRail that wont warp or melt !
* High grade milspec ignition driver electronics now in development
* Twin Tyres to suit most sedans, trikes and motorcycle sidecars
http://niche.iinet.net.au

In article <ypidnXFOXfoz7ePZnZ2dnUVZ_vOdnZ2d@giganews.com>, westes-usc@noemail.nospam says...
>
>Our company has had a long-standing problem where UPS batteries will at
>various points in their lifetime suddenly overheat, sometimes
>catastrophically to the point where the battery casing starts to melt and
>you can actually smell the gases from the battery leaking. So far we have
>been lucky to catch such thermal events with temperature sensors but it has
>always been a goal of mine to better understand why this happens, and to
>find some UPS system where it can be avoided entirely. To date, we have
>seen these problems with APC Symmetra tower, Symmetra rackmount, and
>SmartUPS.
>
>After working with an electrician, I have a theory about why this is
>happening, and if correct, the theory suggests a different design for UPS
>systems that would avoid the problem. I am hoping some manufacturer has
>already implemented this idea and someone can refer me to their products.
>
>On all of the UPS systems we use generic "brick" batteries are joined
>together in a series, then the leads from the ends of these battery chains
>are connected to the UPS. The problem is that batteries rarely fail all
>together. If a 12V battery should be considered discharged and not useful
>at around 10V, and you have two 12V batteries joined in series, what happens
>when one of the batteries maintains a full charge at 12V but the other
>battery in the series starts to lose its ability to hold charge and slips
>below some critical level? From the point of view of the UPS, it
>doesn't see anything about the state of individual batteries. The UPS only
>sees that the total voltage of the two 12V batteries in series has fallen
>from 24V to 22V.
>
>Maybe an electrical engineer can step in here and explain what is happening,
>but my pure guess is that to maintain the same power output, an increased
>amount of current probably has to flow through the batteries. That
>creates problems with heating for the "good" battery, which is still
>measuring 12V. Now that 12V is receiving too much current, overcharges,
>overheats, and at some point the casing of the battery starts to melt. I
>haven't done enough experimentation to determine if it is the good battery
>or bad battery that is overheating. To be honest, in such situations I
>have often seen evidence that both batteries start to melt. Perhaps this
>is nothing more than one battery being in physical proximity to the
>overheating battery and therefore gaining heat from its physical contact.
>The only thing that is common to all cases is that one of the two batteries
>has discharged and should have been replaced before the overheating event
>took place.
>
>Regardless of the actual mechanism for the overheating we are observing, it
>seems to me that the obvious solution is to design UPS systems to physically
>connect to each 12V battery individually. Forget connecting multiple
>batteries in series, at least don't do that at the battery itself. By
>connecting to and monitoring individual batteries, now the UPS can see when
>an individual battery falls below some critical voltage threshold and put it
>into a special recharge state (not put any load on it). If the battery
>fails to recharge, the UPS can declare the battery defective and can signal
>the condition by an LED on the battery's compartment. If there is a
>network attached monitoring system, the UPS can send an e-mail.
>
>Aside from increasing safety and utility of the monitoring system, such a
>design would allow much easier re-use of off-the-shelf batteries, improving
>ease-of-use in making battery changes and lowering cost. While I realize
>that APC in particular has no desire to make anything regarding batteries
>non proprietary, maybe some other vendor has a UPS design that puts a direct
>monitoring circuit on each individual 12V brick battery, thus avoiding the
>overheating problem I have described?
>
>Any information on why this overheating takes place, how to avoid it, and
>any referrals to third party UPS products that employ a more robust design
>are appreciated.
>
>--
>Will
>
>

nicksanspam@ece.villanova.edu

2006-06-01, 4:21 am

Will <westes-usc@noemail.nospam> wrote:

>Regardless of the actual mechanism for the overheating we are observing, it
>seems to me that the obvious solution is to design UPS systems to physically
>connect to each 12V battery individually. Forget connecting multiple
>batteries in series, at least don't do that at the battery itself. By
>connecting to and monitoring individual batteries, now the UPS can see when
>an individual battery falls below some critical voltage threshold and put it
>into a special recharge state (not put any load on it). If the battery
>fails to recharge, the UPS can declare the battery defective and can signal
>the condition by an LED on the battery's compartment. If there is a
>network attached monitoring system, the UPS can send an e-mail.

Or multiple emails, as in:

while true
do
mail westes-usc@noemail.nospam < replacemybatteryfile
sleep 3600
done

An overtemp shutdown might be simpler :-)

Nick

dnoyeB

2006-06-01, 10:21 am

Will wrote:

> Our company has had a long-standing problem where UPS batteries will at
> various points in their lifetime suddenly overheat, sometimes
> catastrophically to the point where the battery casing starts to melt and
> you can actually smell the gases from the battery leaking. So far we
> have been lucky to catch such thermal events with temperature sensors but
> it has always been a goal of mine to better understand why this happens,
> and to
> find some UPS system where it can be avoided entirely. To date, we have
> seen these problems with APC Symmetra tower, Symmetra rackmount, and
> SmartUPS.
>
> After working with an electrician, I have a theory about why this is
> happening, and if correct, the theory suggests a different design for UPS
> systems that would avoid the problem. I am hoping some manufacturer has
> already implemented this idea and someone can refer me to their products.
>
> On all of the UPS systems we use generic "brick" batteries are joined
> together in a series, then the leads from the ends of these battery chains
> are connected to the UPS. The problem is that batteries rarely fail all
> together. If a 12V battery should be considered discharged and not
> useful at around 10V, and you have two 12V batteries joined in series,
> what happens when one of the batteries maintains a full charge at 12V but
> the other battery in the series starts to lose its ability to hold charge
> and slips
> below some critical level? From the point of view of the UPS, it
> doesn't see anything about the state of individual batteries. The UPS
> only sees that the total voltage of the two 12V batteries in series has
> fallen from 24V to 22V.
>
> Maybe an electrical engineer can step in here and explain what is
> happening, but my pure guess is that to maintain the same power output, an
> increased
> amount of current probably has to flow through the batteries. That
> creates problems with heating for the "good" battery, which is still
> measuring 12V. Now that 12V is receiving too much current, overcharges,
> overheats, and at some point the casing of the battery starts to melt.
> I haven't done enough experimentation to determine if it is the good
> battery
> or bad battery that is overheating. To be honest, in such situations I
> have often seen evidence that both batteries start to melt. Perhaps this
> is nothing more than one battery being in physical proximity to the
> overheating battery and therefore gaining heat from its physical contact.
> The only thing that is common to all cases is that one of the two
> batteries has discharged and should have been replaced before the
> overheating event took place.
>
> Regardless of the actual mechanism for the overheating we are observing,
> it seems to me that the obvious solution is to design UPS systems to
> physically
> connect to each 12V battery individually. Forget connecting multiple
> batteries in series, at least don't do that at the battery itself. By
> connecting to and monitoring individual batteries, now the UPS can see
> when an individual battery falls below some critical voltage threshold and
> put it
> into a special recharge state (not put any load on it). If the battery
> fails to recharge, the UPS can declare the battery defective and can
> signal
> the condition by an LED on the battery's compartment. If there is a
> network attached monitoring system, the UPS can send an e-mail.
>
> Aside from increasing safety and utility of the monitoring system, such a
> design would allow much easier re-use of off-the-shelf batteries,
> improving
> ease-of-use in making battery changes and lowering cost. While I realize
> that APC in particular has no desire to make anything regarding batteries
> non proprietary, maybe some other vendor has a UPS design that puts a
> direct monitoring circuit on each individual 12V brick battery, thus
> avoiding the overheating problem I have described?
>
> Any information on why this overheating takes place, how to avoid it, and
> any referrals to third party UPS products that employ a more robust design
> are appreciated.
>

If yoru UPS is not detecting this then get a different UPS. Just because
you supposedly have a good brand does not mean you actually have a good
brand. Especially when you single handedly identify a flaw in their
system.

In fail open situation the low battery will not absorb the energy and the
voltage will raise right away. You will find our your batt is bad when you
try to use it and it runs out quickly.

In fail short situation the low battery will absorb the energy and the
voltage will not raise and the batts will slowly heat up. It should be
detected.

Looks like they just are not checking for fail short.

How can there be enough heat to melt a battery but the temp sensor system
not complain?

budgie

2006-06-01, 10:21 am

On Wed, 31 May 2006 21:45:02 -0700, "Will" <westes-usc@noemail.nospam> wrote:

>Our company has had a long-standing problem where UPS batteries will at
>various points in their lifetime suddenly overheat, sometimes
>catastrophically to the point where the battery casing starts to melt and
>you can actually smell the gases from the battery leaking. So far we have
>been lucky to catch such thermal events with temperature sensors but it has
>always been a goal of mine to better understand why this happens, and to
>find some UPS system where it can be avoided entirely. To date, we have
>seen these problems with APC Symmetra tower, Symmetra rackmount, and
>SmartUPS.
>
>After working with an electrician, I have a theory about why this is
>happening, and if correct, the theory suggests a different design for UPS
>systems that would avoid the problem. I am hoping some manufacturer has
>already implemented this idea and someone can refer me to their products.

IMOE the main reason for the failure of SLA/VRLA batteries in SOHO UPS units is
the charging regime - no more, no less.

Recovery after a discharge is a tradeoff. Do you want minimum recovery to
(substantially) full charge to best position you for a possible follow-up
outage, or a leisurely recovery which treats the battery properly?

The bad news is that you don't get to choose - the UPS manufacturers have made
that decision for you and have opted for the over-zealous rate. This is usually
compounded by an excessively high float voltage. To further shorten the life of
the batteries, the regime is often one of current-limited (too high) constant
voltage (also too high) charging. An example of a far better regime is set out
in the data sheet for the Unitrode/TI UC2906/3906 SLA charge controller chips.
Unfortunately - and yes, there seems to be only bad news - it is usually
impossible to splice in a better charging system without causing the UPS'
monitoring circuits to go apeshit.

>On all of the UPS systems we use generic "brick" batteries are joined
>together in a series, then the leads from the ends of these battery chains
>are connected to the UPS. The problem is that batteries rarely fail all
>together. If a 12V battery should be considered discharged and not useful
>at around 10V, and you have two 12V batteries joined in series, what happens
>when one of the batteries maintains a full charge at 12V but the other
>battery in the series starts to lose its ability to hold charge and slips
>below some critical level? From the point of view of the UPS, it
>doesn't see anything about the state of individual batteries. The UPS only
>sees that the total voltage of the two 12V batteries in series has fallen
>from 24V to 22V.

Indeed it would be good sense to monitor the individual batteries, but these are
price-sensitive products in the SOHO sizes. Certainly there is scope to add a
monitor which reports on voltage differential.

>Maybe an electrical engineer can step in here and explain what is happening,
>but my pure guess is that to maintain the same power output, an increased
>amount of current probably has to flow through the batteries. That
>creates problems with heating for the "good" battery, which is still
>measuring 12V. Now that 12V is receiving too much current, overcharges,
>overheats, and at some point the casing of the battery starts to melt.

You are mixing up discharge and charge in the above, UIAVMM.

>I
>haven't done enough experimentation to determine if it is the good battery
>or bad battery that is overheating. To be honest, in such situations I
>have often seen evidence that both batteries start to melt. Perhaps this
>is nothing more than one battery being in physical proximity to the
>overheating battery and therefore gaining heat from its physical contact.
>The only thing that is common to all cases is that one of the two batteries
>has discharged and should have been replaced before the overheating event
>took place.

By the time one battery in a series string needs replacing, they all should be
replaced. You create the exact situation you referred to above by replacing one
of a series string.

>Regardless of the actual mechanism for the overheating we are observing, it
>seems to me that the obvious solution is to design UPS systems to physically
>connect to each 12V battery individually. Forget connecting multiple
>batteries in series, at least don't do that at the battery itself. By
>connecting to and monitoring individual batteries, now the UPS can see when
>an individual battery falls below some critical voltage threshold and put it
>into a special recharge state (not put any load on it). If the battery
>fails to recharge, the UPS can declare the battery defective and can signal
>the condition by an LED on the battery's compartment. If there is a
>network attached monitoring system, the UPS can send an e-mail.
>
>Aside from increasing safety and utility of the monitoring system, such a
>design would allow much easier re-use of off-the-shelf batteries, improving
>ease-of-use in making battery changes and lowering cost. While I realize
>that APC in particular has no desire to make anything regarding batteries
>non proprietary, maybe some other vendor has a UPS design that puts a direct
>monitoring circuit on each individual 12V brick battery, thus avoiding the
>overheating problem I have described?
>
>Any information on why this overheating takes place, how to avoid it, and
>any referrals to third party UPS products that employ a more robust design
>are appreciated.

The other consideration that compounds battery heating is the way they are
tightly packed into the case. Again, short of mounting them outside - as some
users do - there is little that can be done in mitigation as there simply isn't
room to provide ventilation or additional conduction paths.

Both of the UPS units I have here - 1000VA (5x12V) and 300VA (2x12V) - have the
batteries almost shoe-horned into their place. In fact, there is no way a
shoehorn could fit in there between them. What I have done, though, is
re-engineer the charging circuitry to "better" recovery and float charging
conditions.

William P.N. Smith

2006-06-01, 11:21 am

JoeSP

2006-06-01, 12:21 pm

"Will" <westes-usc@noemail.nospam> wrote in message
news:ypidnXFOXfoz7ePZnZ2dnUVZ_vOdnZ2d@giganews.com...
> Our company has had a long-standing problem where UPS batteries will at
> various points in their lifetime suddenly overheat, sometimes
> catastrophically to the point where the battery casing starts to melt and
> you can actually smell the gases from the battery leaking. So far we
> have
> been lucky to catch such thermal events with temperature sensors but it
> has
> always been a goal of mine to better understand why this happens, and to
> find some UPS system where it can be avoided entirely. To date, we have
> seen these problems with APC Symmetra tower, Symmetra rackmount, and
> SmartUPS.

Best I can offer, is to avoid deep discharges that can sulfate and short the
plates. Then avoid putting batteries in parallel, that can short through
those sulfated plates. Maybe a fusible link between the banks would burn up
instead of the batteries themselves. Another idea is to put 8-10 cells in
series, to give you 120V (number varies with type of cells used) and then
use the inverter alone, without the transformer to convert it to AC.

Jerry Avins

2006-06-01, 12:21 pm

Will wrote:
> Our company has had a long-standing problem where UPS batteries will at
> various points in their lifetime suddenly overheat ...

There's not much to add to the good comments already given. The
important concept is *battery*, i.e., a group of cells. Each 12-volt
battery is 6 2-volt cells in series. It makes no difference if the 20
cells of a 120-volt battery are in one case or several provided they are
well matched. Mixing cells from different production lots is not good
form unless production tolerances are very tight. The only safe way to
use a mix of cells of varying capacity is by charging the cells
individually and discharging them in parallel. Then you need to make
sure that the discharge is stopped when any one cell is depleted.

That's just not practical. You wouldn't mix old and new cells in a
flashlight. Don't do it in a UPS.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Hawk

2006-06-01, 4:21 pm

"Will" <westes-usc@noemail.nospam> wrote :
> Our company has had a long-standing problem where UPS batteries will at
> various points in their lifetime suddenly overheat, sometimes
> catastrophically to the point where the battery casing starts to melt and
> you can actually smell the gases from the battery leaking. So far we have
> been lucky to catch such thermal events with temperature sensors but it has
> always been a goal of mine to better understand why this happens, and to
> find some UPS system where it can be avoided entirely. To date, we have
> seen these problems with APC Symmetra tower, Symmetra rackmount, and
> SmartUPS.
>
> After working with an electrician, I have a theory about why this is
> happening, and if correct, the theory suggests a different design for UPS
> systems that would avoid the problem. I am hoping some manufacturer has
> already implemented this idea and someone can refer me to their products.
>
> On all of the UPS systems we use generic "brick" batteries are joined
> together in a series, then the leads from the ends of these battery chains
> are connected to the UPS. The problem is that batteries rarely fail all
> together. If a 12V battery should be considered discharged and not useful
> at around 10V, and you have two 12V batteries joined in series, what happens
> when one of the batteries maintains a full charge at 12V but the other
> battery in the series starts to lose its ability to hold charge and slips
> below some critical level? From the point of view of the UPS, it
> doesn't see anything about the state of individual batteries. The UPS only
> sees that the total voltage of the two 12V batteries in series has fallen
> from 24V to 22V.
>
> Maybe an electrical engineer can step in here and explain what is happening,
> but my pure guess is that to maintain the same power output, an increased
> amount of current probably has to flow through the batteries. That
> creates problems with heating for the "good" battery, which is still
> measuring 12V. Now that 12V is receiving too much current, overcharges,
> overheats, and at some point the casing of the battery starts to melt. I
> haven't done enough experimentation to determine if it is the good battery
> or bad battery that is overheating. To be honest, in such situations I
> have often seen evidence that both batteries start to melt. Perhaps this
> is nothing more than one battery being in physical proximity to the
> overheating battery and therefore gaining heat from its physical contact.
> The only thing that is common to all cases is that one of the two batteries
> has discharged and should have been replaced before the overheating event
> took place.
>
> Regardless of the actual mechanism for the overheating we are observing, it
> seems to me that the obvious solution is to design UPS systems to physically
> connect to each 12V battery individually. Forget connecting multiple
> batteries in series, at least don't do that at the battery itself. By
> connecting to and monitoring individual batteries, now the UPS can see when
> an individual battery falls below some critical voltage threshold and put it
> into a special recharge state (not put any load on it). If the battery
> fails to recharge, the UPS can declare the battery defective and can signal
> the condition by an LED on the battery's compartment. If there is a
> network attached monitoring system, the UPS can send an e-mail.
>
> Aside from increasing safety and utility of the monitoring system, such a
> design would allow much easier re-use of off-the-shelf batteries, improving
> ease-of-use in making battery changes and lowering cost. While I realize
> that APC in particular has no desire to make anything regarding batteries
> non proprietary, maybe some other vendor has a UPS design that puts a direct
> monitoring circuit on each individual 12V brick battery, thus avoiding the
> overheating problem I have described?
>
> Any information on why this overheating takes place, how to avoid it, and
> any referrals to third party UPS products that employ a more robust design
> are appreciated.
>
> --
> Will

Here is an example of one thing to consider. In a string of cells (or batteries)
you could have one that over time has fallen in usable capacity faster than the
others. In the situation where the entire string is being discharged, the moment
that the weakest cell runs out of capacity it will no longer be contributing to
the load and will essentially be CHARGED BACKWARDS by the discharge current of the
remaining cells.

You will get plenty of gassing and other bad things happening under this scenario.
Depending on the design of the system, it may not even be able to detect that a
cell has effectively dropped out. Obviously this is a bigger problem in higher
voltage battery configurations. For example, you will notice a dead cell in a 4
cell pack much easier than in a 12 cell pack.

(*>

Will

2006-06-01, 4:21 pm

"Will" <westes-usc@noemail.nospam> wrote in message
news:ypidnXFOXfoz7ePZnZ2dnUVZ_vOdnZ2d@giganews.com...
> Our company has had a long-standing problem where UPS batteries will at
> various points in their lifetime suddenly overheat, sometimes
> catastrophically to the point where the battery casing starts to melt and
> you can actually smell the gases from the battery leaking. So far we
have

Thank you to everyone for all the good comments made so far in this thread.
The bottom line seems to be that most smaller UPS systems use a
too-aggressive charging scheme, and pack the batteries too close together,
so that thermal events in one battery quickly spread to other batteries
touching that one.

Does any UPS manufacturer make a unit that will do about 3000VA - rackmount
or tower configuration - that will treat the batteries better and use less
aggressive charging in favor of long battery life? And of those units,
does anyone make a unit where the batteries are given enough space between
them that overheating in one battery stays localized to that battery?

--
Will

Eric Sears

2006-06-01, 5:21 pm

On Thu, 1 Jun 2006 11:59:22 -0700, "Will"
<DELETE_westes@earthbroadcast.com> wrote:

>Does any UPS manufacturer make a unit that will do about 3000VA - rackmount
>or tower configuration - that will treat the batteries better and use less
>aggressive charging in favor of long battery life? And of those units,
>does anyone make a unit where the batteries are given enough space between
>them that overheating in one battery stays localized to that battery?
>
>--
>Will
>
>
I don't know what is available, but if this is what you want (3000VA),
it seems to me that you might be better to put together your own UPS
from discrete units.
It might be larger (do you have room for it?), but it ought to be more
reliable.
Find a reasonable inverter, perhaps one that runs on 12volts (to
mitigate needing too many "cells"), and perhaps use about 20 to 30
amphr SLA (or even bigger) with a quality seperate charger - something
that can provide the power you normally need for you computers, but
also has a proper float charging regime. Run everything through the
inverter all the time.
(Personally I prefer "wet cells" like T105's - but that's probably not
suitable in an office situation - it just that I think they are harder
to kill).
It will be more expensive, but it much easier to monitor. You might
even have a staff member learn to measure the the battery voltage on a
regular basis.

My tuppence worth

Eric Sears

Cameron Dorrough

2006-06-01, 8:21 pm

One idea that has been missed so far: If you are really serious about
reliability (most UPS users aren't) and don't like dealing with batteries,
consider installing a Rotary UPS. You'll find plenty of good info via a
Google search.

I know it's "old school" and more expensive initial outlay, but Rotary UPS's
are used by the majority of the world's Stock Exchanges and major data
centres for all of the reasons you mentioned in your post - and on power
failure, they just work.

HTH,
Cameron:-)

William P.N. Smith

2006-06-01, 8:21 pm

Cameron Dorrough

2006-06-01, 9:21 pm

"William P.N. Smith" <news2006c@compusmiths.com> wrote in message
news:s1tu72hmjmgeo2b4occv0j0nt7ku2568lb@4ax.com...
> "Cameron Dorrough" <cdorrough@nortonconsultants.com> wrote:
>
> Don't Rotary UPSes just provide a few seconds of power while your
> diesel generators are firing up?

I'm sure some are configured that way - that would be a TPS (Temporary Power
Supply). Although it takes a lot longer than a few seconds to run the
flywheel down.

It depends what you buy. The Pillar UPS powering the Melbourne Stock
Exchange (that's Melbourne, Australia - not Melbourne, USA) is rated for 30
minutes at full load.

Cameron:-)

budgie

2006-06-01, 11:21 pm

On Thu, 01 Jun 2006 19:58:26 GMT, phoneme@025379386.for.email.address (Eric
Sears) wrote:

>I don't know what is available, but if this is what you want (3000VA),
>it seems to me that you might be better to put together your own UPS
>from discrete units.
>It might be larger (do you have room for it?), but it ought to be more
>reliable.
>Find a reasonable inverter, perhaps one that runs on 12volts (to
>mitigate needing too many "cells"), and perhaps use about 20 to 30
>amphr SLA (or even bigger)

(snip)

???? a 3000VA inverter is going to want 250A @12V input, assuming 100%
efficiency. There IS a reason why higher input voltages are used as the output
rating climbs. Even my 1000VA unit runs a 60V string of 5*12V.

budgie

2006-06-01, 11:21 pm

On Fri, 2 Jun 2006 09:45:40 +1000, "Cameron Dorrough"
<cdorrough@nortonconsultants.com> wrote:

>"William P.N. Smith" <news2006c@compusmiths.com> wrote in message
>news:s1tu72hmjmgeo2b4occv0j0nt7ku2568lb@4ax.com...
>
>I'm sure some are configured that way - that would be a TPS (Temporary Power
>Supply). Although it takes a lot longer than a few seconds to run the
>flywheel down.
>
>It depends what you buy. The Pillar UPS powering the Melbourne Stock
>Exchange (that's Melbourne, Australia - not Melbourne, USA) is rated for 30
>minutes at full load.

When I had to re-engineer the power systems at a large govt computing centre
here in Perth (Oz) we looked at several rotary systems. They all relied on the
flywheel energy to cover the break until the backup diesel genset(s) start. One
rather large bank's head office had this config with ONE diesel alternator. The
outlook if it fails to fire is rather bleak.

I opted for three parallelled 300kVA UPS units, with inherent redundancy as we
had a base load below 600kVA. I also added a third diesel set to the existing
pair, bringing total diesel-generated output to ~1500kVA. Again, redundancy -
and necessary capacity.

I don't "like" large battery banks, but I would never seriously consider a
rotary storage system in any critical application. And I doubt there is a
rotary offering in the O/P's 3kVA size.

Jerry Avins

2006-06-01, 11:21 pm

budgie wrote:

> On Fri, 2 Jun 2006 09:45:40 +1000, "Cameron Dorrough"
> <cdorrough@nortonconsultants.com> wrote:
>
>
>
>
> When I had to re-engineer the power systems at a large govt computing centre
> here in Perth (Oz) we looked at several rotary systems. They all relied on the
> flywheel energy to cover the break until the backup diesel genset(s) start. One
> rather large bank's head office had this config with ONE diesel alternator. The
> outlook if it fails to fire is rather bleak.
>
> I opted for three parallelled 300kVA UPS units, with inherent redundancy as we
> had a base load below 600kVA. I also added a third diesel set to the existing
> pair, bringing total diesel-generated output to ~1500kVA. Again, redundancy -
> and necessary capacity.
>
> I don't "like" large battery banks, but I would never seriously consider a
> rotary storage system in any critical application. And I doubt there is a
> rotary offering in the O/P's 3kVA size.

Years ago, when wet cells were the only game, we ran a synchronous
generator as a motor driving a flywheel. When power dropped, the
contactor to the line did too, and a clutch engaged an internal
combustion engine that ran on illuminating gas. The system never failed,
but short dropouts -- they're more frequent than we had imagined -- were
painful. Switching back to line power required that the generator be
phase locked by hand before the contactor was re-energized. We couldn't
let the flywheel carry the load while the contactor remained closed for
the obvious reason.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Will

2006-06-02, 12:21 am

"budgie" <me@privacy.net> wrote in message
news:5cot72lk5oksb8e73idjmnbudm2vs952i9@4ax.com...
> Recovery after a discharge is a tradeoff. Do you want minimum recovery to
> (substantially) full charge to best position you for a possible follow-up
> outage, or a leisurely recovery which treats the battery properly?
>
> The bad news is that you don't get to choose - the UPS manufacturers have
made
> that decision for you and have opted for the over-zealous rate. This is
usually
> compounded by an excessively high float voltage. To further shorten the
life of
> the batteries, the regime is often one of current-limited (too high)
constant
> voltage (also too high) charging. An example of a far better regime is
set out
> in the data sheet for the Unitrode/TI UC2906/3906 SLA charge controller
chips.
> Unfortunately - and yes, there seems to be only bad news - it is usually
> impossible to splice in a better charging system without causing the UPS'
> monitoring circuits to go apeshit.

Could you reformulate the above statements as a set of requirements I can
put into a requirements document for a new UPS? I'm guessing that the
requirements would be something similar to the following, but I am hoping
you will make these statements more precise:

- UPS should use a recharge / recovery scheme that maximizes battery
lifetime rather than minimizing recharge times, or should as a worst case
allow this to be a user configurable option.

- UPS should use an appropriate float voltage for the batteries it uses.

- UPS should allow the use of deep cycle batteries.

- UPS should provide a way to use an appropriate topping charge every six
months with the battery.

> By the time one battery in a series string needs replacing, they all
should be
> replaced. You create the exact situation you referred to above by
replacing one
> of a series string.

If I take an older UPS gel-cell battery which is in series as 2 x 12V, and I
test each 12V and find that one is giving a good 12V reading when charged
and the other never goes above 10V, why can't I just replace the dead 10V
battery with a fresher 12V? How is replacing the dying battery promoting
overheating?

--
Will

Jerry Avins

2006-06-02, 12:21 am

Will wrote:

...

> If I take an older UPS gel-cell battery which is in series as 2 x 12V, and I
> test each 12V and find that one is giving a good 12V reading when charged
> and the other never goes above 10V, why can't I just replace the dead 10V
> battery with a fresher 12V? How is replacing the dying battery promoting
> overheating?

You can replace only the bad one*, but expect short life from the one
not replaced.

Jerry
__________________________________
* You might even revive the bad one by floating it separately. Don't
rely heavily on it, though.
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

wireless@tampabay.rr.com

2006-06-02, 12:21 am

Will wrote:

> Our company has had a long-standing problem where UPS batteries will at
> various points in their lifetime suddenly overheat, sometimes
> catastrophically to the point where the battery casing starts to melt and
> you can actually smell the gases from the battery leaking. So far we
> have been lucky to catch such thermal events with temperature sensors but
> it has always been a goal of mine to better understand why this happens,
> and to
> find some UPS system where it can be avoided entirely. To date, we have
> seen these problems with APC Symmetra tower, Symmetra rackmount, and
> SmartUPS.
>
> After working with an electrician, I have a theory about why this is
> happening, and if correct, the theory suggests a different design for UPS
> systems that would avoid the problem. I am hoping some manufacturer has
> already implemented this idea and someone can refer me to their products.

This is a very complex problem and the best solutions are EXPENSIVE!

Well your industrial electrician should have first told you (electricity
101) that you need a PM( Preventative Maintenance) schedule on UPSes.
This would involved thaking the UPS offline monthly/quarterly and testing
the batteries and other portions of the UPS. The industrial size UPS all
come with offers from 3rd party companies to perform PM on you UPS gear.
If you buy cheap equipment, a quality 3rd party company (which will usually
also sell you an extended warranty as part of the PM) will tell you to buy
something industrial grade, like a 3-phase UPS that is interfaces to a
Gen_Set.

Also I always design UPS systems, no matter how large, to have a
1:1 isolation transformer upstream of the all power feedeing the UPS.
This eliminates most power quality problems from the local utility
or the XXX_hole down the street that is wreaking havoc on the electrical
grid because he's using a 3phase welder and the idiot that run the
utility commissions (here in the US) or elsewhere to not have the common
sense to test/monitor and require such folk to put in equipment
to mitigate the effects of certain types of industrial equipment
on the electrical grid. (expensive equipment will allow you to monitor
the power quality (or lack thereof) from you local electrical utility feed.

>
> On all of the UPS systems we use generic "brick" batteries are joined
> together in a series, then the leads from the ends of these battery chains
> are connected to the UPS. The problem is that batteries rarely fail all
> together. If a 12V battery should be considered discharged and not
> useful at around 10V, and you have two 12V batteries joined in series,
> what happens when one of the batteries maintains a full charge at 12V but
> the other battery in the series starts to lose its ability to hold charge
> and slips
> below some critical level? From the point of view of the UPS, it
> doesn't see anything about the state of individual batteries. The UPS
> only sees that the total voltage of the two 12V batteries in series has
> fallen from 24V to 22V.
>
> Maybe an electrical engineer can step in here and explain what is
> happening,

UPS batteries and battery charging circuits and semiconductors leave much
to be desired. If you spend some time researching 'gel-cel' batteries and
other types of batteries used in UPSes, you find there are subtle
difference in the batteries. When these differences are combined with
with poorly designed charging circuits are poorly chosen semiconductors
in the charging circuitry, trade offs are made. These are compounded
by subtle differences in the electrical characteristics of different
batteries supplied from a variety of low_cost suppliers.

If you look at battery charging semi conductors, such as those
provide my Maxim, you can read the data sheets for some really
good/detailed discussions on a myriad of issues related to this
complex problem.

> but my pure guess is that to maintain the same power output, an
> increased
> amount of current probably has to flow through the batteries. That
> creates problems with heating for the "good" battery, which is still
> measuring 12V. Now that 12V is receiving too much current, overcharges,
> overheats, and at some point the casing of the battery starts to melt.
> I haven't done enough experimentation to determine if it is the good
> battery
> or bad battery that is overheating. To be honest, in such situations I
> have often seen evidence that both batteries start to melt. Perhaps this
> is nothing more than one battery being in physical proximity to the
> overheating battery and therefore gaining heat from its physical contact.
> The only thing that is common to all cases is that one of the two
> batteries has discharged and should have been replaced before the
> overheating event took place.
>
> Regardless of the actual mechanism for the overheating we are observing,
> it seems to me that the obvious solution is to design UPS systems to
> physically
> connect to each 12V battery individually. Forget connecting multiple
> batteries in series, at least don't do that at the battery itself. By
> connecting to and monitoring individual batteries, now the UPS can see
> when an individual battery falls below some critical voltage threshold and
> put it
> into a special recharge state (not put any load on it). If the battery
> fails to recharge, the UPS can declare the battery defective and can
> signal
> the condition by an LED on the battery's compartment. If there is a
> network attached monitoring system, the UPS can send an e-mail.
>
> Aside from increasing safety and utility of the monitoring system, such a
> design would allow much easier re-use of off-the-shelf batteries,
> improving
> ease-of-use in making battery changes and lowering cost. While I realize
> that APC in particular has no desire to make anything regarding batteries
> non proprietary, maybe some other vendor has a UPS design that puts a
> direct monitoring circuit on each individual 12V brick battery, thus
> avoiding the overheating problem I have described?
>
> Any information on why this overheating takes place, how to avoid it, and
> any referrals to third party UPS products that employ a more robust design
> are appreciated.

Overheating is unfortunately a vestige of a variety of problems with this
complex issue. Search and read as much of this information is available via
googling the net.......

HTH,

James

wireless@tampabay.rr.com

2006-06-02, 12:21 am

Will wrote:

> Does any UPS manufacturer make a unit that will do about 3000VA -
> rackmount or tower configuration - that will treat the batteries better
> and use less
> aggressive charging in favor of long battery life? And of those units,
> does anyone make a unit where the batteries are given enough space between
> them that overheating in one battery stays localized to that battery?

On smaller UPS systems ( less that 10,000 VA) I'd suggest you make sure
the UPS vendor uses a 'ferro-resonant' transformer in the UPS. It is a big
heavy iron core that will filter most power quality feed problems
(particularly transients) out from the utility power feed, thus making the
UPS more durable and less transient electrical effects that deteriorate
the solid state components and the batteries in the UPS.

BEST use to make a 'Ferrups' but they sold out and you have to do
your research as this sort of UPS will be larger, much heavier
and definitely more expensive. Alternatively, you can get use cheap UPSes
and get your electrician to install a big 1:1 (one to one) isolation
transformer upstream of all of the upses in your facility.

If you get an industrial grade UPS as the vendor about 3rd party maintenance
PM costs and extended warranties which include PM or do the PM yourself
(if you are a qualified electrician)....

HTH,

James

budgie

2006-06-02, 3:21 am

On Thu, 1 Jun 2006 19:31:20 -0700, "Will" <westes-usc@noemail.nospam> wrote:
>
>Could you reformulate the above statements as a set of requirements I can
>put into a requirements document for a new UPS? I'm guessing that the
>requirements would be something similar to the following, but I am hoping
>you will make these statements more precise:
>
>- UPS should use a recharge / recovery scheme that maximizes battery
>lifetime rather than minimizing recharge times, or should as a worst case
>allow this to be a user configurable option.
>
>- UPS should use an appropriate float voltage for the batteries it uses.

I avoid the word "should" in specifications. Unless you intend to scour
responses with a fine tooth comb and solicit clause-by-clause statements of
compliance, you are wasting your time. Even then, if the supplier states
"comply" to a "should", it doesn't mean he actually DOES what you preferred. I
"should" eat less fatty food, but I don't.

Focus on the recovery time, and maximum recharge current being less than (say)
60% of manufacturer's recommended max charge rate - the derating being for
thermal reasons given that the MR figure will usually be free air rated.

Focus on float voltage being whatever gives about 85-90% S.O.C. Any higher and
you WILL progressively cook the batteries.

>- UPS should allow the use of deep cycle batteries.

?? Deep cycle vs SLA/VRLA. You need to decide on one battery type.

I'm not sure whether you are looking at the 3kVA size or not, so battery choice
and ventilation are unknowns here. SLA's are widely used simply because they
avoid ventilation issues.

I'm also not sure whether you are buying one or a hundred. Writing a spec for
one is a bit of overkill unless it is BIG (50kVA or more), otherwise just keep
the spec as purchasing guidelines to enable interrogation of wannabe suppliers.

>- UPS should provide a way to use an appropriate topping charge every six
>months with the battery.

Not only pointless, but probably deleterious in gelled electrolyte types. See
above re battery type.

>should be
>replacing one
>
>If I take an older UPS gel-cell battery which is in series as 2 x 12V, and I
>test each 12V and find that one is giving a good 12V reading when charged
>and the other never goes above 10V, why can't I just replace the dead 10V
>battery with a fresher 12V? How is replacing the dying battery promoting
>overheating?

By the time one battery has died - unless we are talking of infant mortality -
it's mates have been subject to the same regime of use/abuse, and should be
replaced before they follow. You are creating a series string of unequals, which
is a recipe for failure. It's almost like changing tyres one at a time, except
with tyres you can at least see their condition. False economy.

budgie

2006-06-02, 3:21 am

On Thu, 01 Jun 2006 21:58:39 -0400, Jerry Avins <jya@ieee.org> wrote:

>budgie wrote:
>
>
>Years ago, when wet cells were the only game, we ran a synchronous
>generator as a motor driving a flywheel. When power dropped, the
>contactor to the line did too, and a clutch engaged an internal
>combustion engine that ran on illuminating gas. The system never failed,
>but short dropouts -- they're more frequent than we had imagined -- were
>painful. Switching back to line power required that the generator be
>phase locked by hand before the contactor was re-energized. We couldn't
>let the flywheel carry the load while the contactor remained closed for
>the obvious reason.

Geez, Jerry, autosync has been around for ages.

In our configuration, the three gensets were (obviously) all initiated after the
outage had lasted 15 secs. They were 2*300kVA and the added one was 900kVA. We
used a PLC to set the rules: if the 300's were up and the 900 wasn't, they
would attempt to parallel (autosync) off-load and then connect to the gen bus.
If the 900 came up and the others weren't already on the bus (the usual case) it
would connect, and the others would then abandon their off-load parallelling
attempts and join individually.

It took a bit of fine tuning to handle the dynamics of different sized machines,
but it worked a treat. Worst case when all three fired was about 50 secs to
have them all parallelled on load.

I have seen the in-line prime-mover, alternator, motor combos. My main issue
with them was the frequency drop when the flywheel accelerated the prime mover
up from 0 to 1500 (1800 your side?) rpm.

The rotary that the big bank HO used was by "HH". It ran a controlled fluid
coupling, with the flywheel at ~3000rpm. Once motor drive failed, as the
flywheel decelerated the coupling was controlled so the alternator remained at
line frequency. But you only had a finite (read *short*) time to get the prime
mover(s) up. And really only one shot.

Our PM's were Detroit two-strokes. The 900kVA would be at speed within seven
secs of the start of cranking - presuming it fired of course. But a failure to
fire withing 30 secs would be the end of the bank (who also used a DD prime
mover on their genset).

Will

2006-06-02, 4:21 am

"budgie" <me@privacy.net> wrote in message
news:n8iv72tgf9kue7mhgaguvg5ciah6tj97mq@4ax.com...
>Focus on float voltage being whatever gives about 85-90% S.O.C. Any higher
and
>you WILL progressively cook the batteries

What is "S.O.C."?

> ?? Deep cycle vs SLA/VRLA. You need to decide on one battery type.

I guess deep cycle would be a better choice for battery life, but probably
requires a lot of additional cost and no one will support them in a smaller
UPS?

--
Will

Jasen Betts

2006-06-02, 7:21 am

On 2006-06-01, Will <westes-usc@noemail.nospam> wrote:
> Our company has had a long-standing problem where UPS batteries will at
> various points in their lifetime suddenly overheat, sometimes
> catastrophically to the point where the battery casing starts to melt and
> you can actually smell the gases from the battery leaking. So far we have
> been lucky to catch such thermal events with temperature sensors but it has
> always been a goal of mine to better understand why this happens, and to
> find some UPS system where it can be avoided entirely. To date, we have
> seen these problems with APC Symmetra tower, Symmetra rackmount, and
> SmartUPS.

a shorted cell could do that if you've batteries in parallel.

> Maybe an electrical engineer can step in here and explain what is happening,
> but my pure guess is that to maintain the same power output, an increased
> amount of current probably has to flow through the batteries. That
> creates problems with heating for the "good" battery, which is still
> measuring 12V. Now that 12V is receiving too much current, overcharges,
> overheats, and at some point the casing of the battery starts to melt.

It'd lots of power for that to happen. many UPSs only charge at a low rate...

> Regardless of the actual mechanism for the overheating we are observing, it
> seems to me that the obvious solution is to design UPS systems to physically
> connect to each 12V battery individually. Forget connecting multiple
> batteries in series, at least don't do that at the battery itself. By
> connecting to and monitoring individual batteries, now the UPS can see when
> an individual battery falls below some critical voltage threshold and put it
> into a special recharge state (not put any load on it).

> If the battery
> fails to recharge, the UPS can declare the battery defective and can signal
> the condition by an LED on the battery's compartment. If there is a
> network attached monitoring system, the UPS can send an e-mail.

If a battery fails it's time to replace all of them
either they failed early and it's possiblty a bad batch,
or you've missed the due date to replace them.

Bye.
Jasen

budgie

2006-06-02, 8:21 am

William P.N. Smith

2006-06-02, 9:21 am

"Will" <westes-usc@noemail.nospam> wrote:
>If I take an older UPS gel-cell battery which is in series as 2 x 12V, and I
>test each 12V and find that one is giving a good 12V reading when charged
>and the other never goes above 10V, why can't I just replace the dead 10V
>battery with a fresher 12V? How is replacing the dying battery promoting
>overheating?

Ah, we've discovered the problem with your existing UPSen.

First, replace the batteries on a regular schedule, before they fail.

Second, battery strings must be matched, so replace all the batteries
in a string at the same time.

Please note: You haven't specified your requirements very well. The
answers for hundreds of kilowatts of UPS for a stock exchange and a
few kilowatts for a local business are significantly different, and
you are getting answers all over the map.

nicksanspam@ece.villanova.edu

2006-06-02, 9:21 am

William P.N. Smith <news2006c@compusmiths.com> wrote:

>... replace the batteries on a regular schedule, before they fail.

Sounds expensive, vs periodically testing and replacing any that don't
pass the test.

>Second, battery strings must be matched, so replace all the batteries
>in a string at the same time.

Sounds expensive. How well-matched must they be?

Nick

William P.N. Smith

2006-06-02, 9:21 am

Jerry Avins

2006-06-02, 12:21 pm

budgie wrote:

...

>
>
> Geez, Jerry, autosync has been around for ages.

So have I. :-)

> In our configuration, the three gensets were (obviously) all initiated after the
> outage had lasted 15 secs. They were 2*300kVA and the added one was 900kVA. We
> used a PLC to set the rules: if the 300's were up and the 900 wasn't, they
> would attempt to parallel (autosync) off-load and then connect to the gen bus.
> If the 900 came up and the others weren't already on the bus (the usual case) it
> would connect, and the others would then abandon their off-load parallelling
> attempts and join individually.

We were a lot smaller than that, about 12 KVA, kludged together from war
surplus equipment.

> It took a bit of fine tuning to handle the dynamics of different sized machines,
> but it worked a treat. Worst case when all three fired was about 50 secs to
> have them all parallelled on load.

Great fun when you get it all working.

> I have seen the in-line prime-mover, alternator, motor combos. My main issue
> with them was the frequency drop when the flywheel accelerated the prime mover
> up from 0 to 1500 (1800 your side?) rpm.

We have turbines at the sewage plant that run on Diesel fuel, with
gravity feed from 500-gallon tanks indoors and the rest of the storage
underground. They are set to wait 45 seconds before starting, and go on
line 15 seconds later. It takes another minute or so for frequency to
settle to spec, but not much cares. The pumps and aerators can wait a
bit. The local power plant uses similar turbines to run their peaking
generators, but they are on turning gear when idle. Ours can wait still.

> The rotary that the big bank HO used was by "HH". It ran a controlled fluid
> coupling, with the flywheel at ~3000rpm. Once motor drive failed, as the
> flywheel decelerated the coupling was controlled so the alternator remained at
> line frequency. But you only had a finite (read *short*) time to get the prime
> mover(s) up. And really only one shot.
>
> Our PM's were Detroit two-strokes. The 900kVA would be at speed within seven
> secs of the start of cranking - presuming it fired of course. But a failure to
> fire withing 30 secs would be the end of the bank (who also used a DD prime
> mover on their genset).

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

repatch

2006-06-02, 3:21 pm

On Fri, 02 Jun 2006 07:45:03 -0400, nicksanspam wrote:

> William P.N. Smith <news2006c@compusmiths.com> wrote:
>
>
> Sounds expensive, vs periodically testing and replacing any that don't
> pass the test.

It is expensive, but you have to do it, since by replacing battery per
battery you will end up with a string of unmatched batteries in various
states of degredation. That's a perfect recipe for the symptoms you've
described.

The NUMBER ONE rule of "battery packs" is strings of batteries must be
replaced at the same time, no mixing and matching is allowed.

>
> Sounds expensive. How well-matched must they be?

Same date code is the only thing I'd be happy with.

TTYL

Jerry Avins

2006-06-02, 3:21 pm

repatch wrote:

> On Fri, 02 Jun 2006 07:45:03 -0400, nicksanspam wrote:

...

>
>
> Same date code is the only thing I'd be happy with.

And, of course, same maker and model number.

It's simple, really. Once one cell in a team dies of old age, it's time
to treat its buddies as honored veterans and put them out to pasture.
Used individually instead of hitched as a team, they may have a useful
contribution in a high-school lab or science club.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

nicksanspam@ece.villanova.edu

2006-06-02, 6:21 pm

repatch <repatch42@yahoo.com> wrote:

>On Fri, 02 Jun 2006 07:45:03 -0400, nicksanspam wrote:
>
>
>It is expensive, but you have to do it, since by replacing battery per
>battery you will end up with a string of unmatched batteries in various
>states of degredation. That's a perfect recipe for the symptoms you've
>described.

I haven't described any symptoms.

>The NUMBER ONE rule of "battery packs" is strings of batteries must be
>replaced at the same time, no mixing and matching is allowed.

According to "solar consultant" George Ghio? :-)

>
>Same date code is the only thing I'd be happy with.

Spoken like a hide-bound bureaucrat :-) How about matching voltages within
some range or equivalent series resistances? Given a max charging current,
we could use these imbalances to predict the max temp rise.

Nick

2006-06-02, 6:21 pm

"Cameron Dorrough" <cdorrough@nortonconsultants.com> wrote:

>One idea that has been missed so far: If you are really serious about
>reliability (most UPS users aren't) and don't like dealing with batteries,
>consider installing a Rotary UPS. You'll find plenty of good info via a
>Google search.
>

BZZZT, won't work. Rotary UPS systems still use batteries, and still
have all of the attendant problems. You are perhaps thinking of
Flywheel UPS systems. THose, while they work for the VERY short term,
give support in time periods measured in SECONDS, and require (on the
ones I have worked on) several minutes to HOURS to recharge the fly
wheel. They also have a low KW/KHW support per sq ft of consumed
space in my opinion.

>I know it's "old school" and more expensive initial outlay, but Rotary UPS's
>are used by the majority of the world's Stock Exchanges and major data
>centres for all of the reasons you mentioned in your post - and on power
>failure, they just work.

On all of the data centers I have worked on, only two had rotary UPS
systems, and only one had a flywheel system. Certainly not the
majority.

>
>HTH,
>Cameron:-)
>

jk

2006-06-02, 6:21 pm

"Cameron Dorrough" <cdorrough@nortonconsultants.com> wrote:

>One idea that has been missed so far: If you are really serious about
>reliability (most UPS users aren't)

Truer words were never typed. Amazing isn't it, how much money people
will spend to ALMOST have reliable power to "Mission critical"
systems.

jk

Peter Bennett

2006-06-02, 7:21 pm

On Thu, 1 Jun 2006 23:28:26 -0700, "Will" <westes-usc@noemail.nospam>
wrote:

>"budgie" <me@privacy.net> wrote in message
>news:n8iv72tgf9kue7mhgaguvg5ciah6tj97mq@4ax.com...
>and
>
>What is "S.O.C."?
>
>
>
>I guess deep cycle would be a better choice for battery life, but probably
>requires a lot of additional cost and no one will support them in a smaller
>UPS?

Deep cycle batteries can be had as flooded cell, gel or AGM (gel and
AGM are also known as SLA/VRLA.

I'm not sure that a deep cycle battery is the best type for a UPS,
since a UPS will demand fairly high currents from the batteries when
supplying power - as I understand it, deep cycle batteries are
optimized for delivering low to moderate currents over a long period,
and to survive many charge/discharge cycles. I would expect most UPS
applications to have very few charge/discharge cycles (unless the
power service is _very_ poor).

--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq

Peter Bennett

2006-06-02, 7:21 pm

On 2 Jun 2006 07:45:03 -0400, nicksanspam@ece.villanova.edu wrote:

>William P.N. Smith <news2006c@compusmiths.com> wrote:

>
>Sounds expensive. How well-matched must they be?
>
>Nick

Quite well - since two batteries permanently connected in series are
acting as a single battery, all cells will have the same "life
experience". Chances are that when one cell fails, most of others are
nearing end-of-life.

--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq

Will

2006-06-02, 8:21 pm

"William P.N. Smith" <news2006c@compusmiths.com> wrote in message
news:8oa082laev3l0g698qa28gr212uk519k69@4ax.com...
> I wonder if you don't have a bit of confusion between cause and effect
> here. Old batteries can short a cell when the plates age (and swell)
> sufficiently, generating quite a bit of heat when the stored energy in
> that cell is released. This _can_ cause an avalanche effect in nearby
> cells and batteries, but the primary cause is ignoring the PM schedule
> on battery replacement...

When testing batteries, is there some key sign that might disclose imminent
failure of one of the 12V bricks? Would we for example see the voltage
decline in a non-linear way as it declines from 12V to 10V?

--
Will

William P.N. Smith

2006-06-02, 8:21 pm

"Will" <westes-usc@noemail.nospam> wrote:
>When testing batteries, is there some key sign that might disclose imminent
>failure of one of the 12V bricks? Would we for example see the voltage
>decline in a non-linear way as it declines from 12V to 10V?

You might notice a decrease in capacity, but since they are gelled
batteries, you aren't going to be able to watch the voltage on
individual cells or test the specific gravity of the electrolyte, so
your best bet is (quick, cover your ears!) to replace them on a
regular basis to avoid end-of-life phenomena.

Jerry Avins

2006-06-02, 8:21 pm

nicksanspam@ece.villanova.edu wrote:

...

> Spoken like a hide-bound bureaucrat :-) How about matching voltages within
> some range or equivalent series resistances? Given a max charging current,
> we could use these imbalances to predict the max temp rise.

Only if you know that the internal construction of each unit is the
same. Cells are designed specifically to hide any symptom of sulfation
for as long as possible, The laudable goal is building a cell that
behaves as much like new as long as possible. Eventually, it falls apart
quickly.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Jerry Avins

2006-06-02, 8:21 pm

Will wrote:

> "William P.N. Smith" <news2006c@compusmiths.com> wrote in message
> news:8oa082laev3l0g698qa28gr212uk519k69@4ax.com...
>
>
>
> When testing batteries, is there some key sign that might disclose imminent
> failure of one of the 12V bricks? Would we for example see the voltage
> decline in a non-linear way as it declines from 12V to 10V?

Back in the days of six-volt car batteries, they tested individual
cell's short-circuit current. Anything less than 250 amps indicated
immanent failure.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

nicksanspam@ece.villanova.edu

2006-06-02, 8:21 pm

Peter Bennett <peterbb@nowhere.invalid> wrote:

>
>
>Quite well...

Got numbers?

Nick

William P.N. Smith

2006-06-02, 10:21 pm

nicksanspam@ece.villanova.edu wrote:
>Given a max charging current,
>we could use these imbalances to predict the max temp rise.

But the meltdown doesn't come from charging current, it comes from
internal shorting of a cell quickly converting all it's stored energy
to heat.

Will

2006-06-02, 11:21 pm

Out of curiosity, would there be a detectable temperature increase prior to
the shorting event within the battery? If you saw increasing internal
temperatures at a point in time (like night) when outside temperatures are
falling, might that be a clue that the battery's failure is imminent?

--
Will

"William P.N. Smith" <news2006c@compusmiths.com> wrote in message
news:jun182tbr5nq2tin60mi75s8evaksspo7d@4ax.com...
> nicksanspam@ece.villanova.edu wrote:
>
> But the meltdown doesn't come from charging current, it comes from
> internal shorting of a cell quickly converting all it's stored energy
> to heat.

Jerry Avins

2006-06-02, 11:21 pm

William P.N. Smith wrote:
> nicksanspam@ece.villanova.edu wrote:
>
>
>
> But the meltdown doesn't come from charging current, it comes from
> internal shorting of a cell quickly converting all it's stored energy
> to heat.

And the heat shorts the neighboring cells. It works both ways.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Jerry Avins

2006-06-02, 11:21 pm

Will wrote:

> Out of curiosity, would there be a detectable temperature increase prior to
> the shorting event within the battery? If you saw increasing internal
> temperatures at a point in time (like night) when outside temperatures are
> falling, might that be a clue that the battery's failure is imminent?

The shorting process is accelerated by heat. If you notice the external
temperature of a battery rising spontaneously, you may have less than
five minutes to cut it loose, probably less than half an hour.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

William P.N. Smith

2006-06-02, 11:21 pm

Jerry Avins <jya@ieee.org> wrote:
>And the heat shorts the neighboring cells. It works both ways.

Right, it's a thermal runaway. Hard to predict, hard to control, easy
to avoid.

budgie

2006-06-03, 1:21 am

On Fri, 02 Jun 2006 21:04:37 -0400, William P.N. Smith
<news2006c@compusmiths.com> wrote:

>nicksanspam@ece.villanova.edu wrote:
>
>But the meltdown doesn't come from charging current, it comes from
>internal shorting of a cell quickly converting all it's stored energy
>to heat.

and the subsequent damage by a none-too-bright charging system.

budgie

2006-06-03, 1:21 am

On Fri, 2 Jun 2006 15:26:09 -0700, "Will" <westes-usc@noemail.nospam> wrote:

>"William P.N. Smith" <news2006c@compusmiths.com> wrote in message
>news:8oa082laev3l0g698qa28gr212uk519k69@4ax.com...
>
>When testing batteries, is there some key sign that might disclose imminent
>failure of one of the 12V bricks? Would we for example see the voltage
>decline in a non-linear way as it declines from 12V to 10V?

Sometimes - but certainly not always - you can detect slight bulging of the case
which pre-empts failure in SLA's. Apart from that, as others have pointed out,
failure can be rather sudden and without warning, especially if it results from
internal shorting.

You MAY be able to pick other types of deterioration by ESR measurements, but I
have never bothered. Also sometimes timing a regular test run to cutoff will
give early warning. But neither reliably warns of an impending shorted cell.

budgie

2006-06-03, 1:21 am

On Fri, 02 Jun 2006 18:59:31 -0400, Jerry Avins <jya@ieee.org> wrote:

>Will wrote:
>
>
>Back in the days of six-volt car batteries, they tested individual
>cell's short-circuit current. Anything less than 250 amps indicated
>immanent failure.

and then the manufacturers decided to bury the inter-cell links where you
couldn't access them without drilling into the wet chambers.

Roy L. Fuchs

2006-06-03, 4:21 am

On Wed, 31 May 2006 21:45:02 -0700, "Will" <westes-usc@noemail.nospam>
Gave us:

>Any information on why this overheating takes place, how to avoid it, and
>any referrals to third party UPS products that employ a more robust design
>are appreciated.

Lead acid gel cells exhibit heat when charged. It is a simple fact.
Period.

Peter Dettmann

2006-06-03, 4:21 am

On Wed, 31 May 2006 21:45:02 -0700, "Will" <westes-usc@noemail.nospam>
wrote:

You also have probelms keeping your posts just to appropriate news
groups. SPAM is what is is.

Peter Dettmann

>Our company has had a long-standing problem where UPS batteries will at
>various points in their lifetime suddenly overheat, sometimes
>catastrophically to the point where the battery casing starts to melt and
>you can actually smell the gases from the battery leaking. So far we have
>been lucky to catch such thermal events with temperature sensors but it has
>always been a goal of mine to better understand why this happens, and to
>find some UPS system where it can be avoided entirely. To date, we have
>seen these problems with APC Symmetra tower, Symmetra rackmount, and
>SmartUPS.
>
>After working with an electrician, I have a theory about why this is
>happening, and if correct, the theory suggests a different design for UPS
>systems that would avoid the problem. I am hoping some manufacturer has
>already implemented this idea and someone can refer me to their products.
>
>On all of the UPS systems we use generic "brick" batteries are joined
>together in a series, then the leads from the ends of these battery chains
>are connected to the UPS. The problem is that batteries rarely fail all
>together. If a 12V battery should be considered discharged and not useful
>at around 10V, and you have two 12V batteries joined in series, what happens
>when one of the batteries maintains a full charge at 12V but the other
>battery in the series starts to lose its ability to hold charge and slips
>below some critical level? From the point of view of the UPS, it
>doesn't see anything about the state of individual batteries. The UPS only
>sees that the total voltage of the two 12V batteries in series has fallen
>from 24V to 22V.
>
>Maybe an electrical engineer can step in here and explain what is happening,
>but my pure guess is that to maintain the same power output, an increased
>amount of current probably has to flow through the batteries. That
>creates problems with heating for the "good" battery, which is still
>measuring 12V. Now that 12V is receiving too much current, overcharges,
>overheats, and at some point the casing of the battery starts to melt. I
>haven't done enough experimentation to determine if it is the good battery
>or bad battery that is overheating. To be honest, in such situations I
>have often seen evidence that both batteries start to melt. Perhaps this
>is nothing more than one battery being in physical proximity to the
>overheating battery and therefore gaining heat from its physical contact.
>The only thing that is common to all cases is that one of the two batteries
>has discharged and should have been replaced before the overheating event
>took place.
>
>Regardless of the actual mechanism for the overheating we are observing, it
>seems to me that the obvious solution is to design UPS systems to physically
>connect to each 12V battery individually. Forget connecting multiple
>batteries in series, at least don't do that at the battery itself. By
>connecting to and monitoring individual batteries, now the UPS can see when
>an individual battery falls below some critical voltage threshold and put it
>into a special recharge state (not put any load on it). If the battery
>fails to recharge, the UPS can declare the battery defective and can signal
>the condition by an LED on the battery's compartment. If there is a
>network attached monitoring system, the UPS can send an e-mail.
>
>Aside from increasing safety and utility of the monitoring system, such a
>design would allow much easier re-use of off-the-shelf batteries, improving
>ease-of-use in making battery changes and lowering cost. While I realize
>that APC in particular has no desire to make anything regarding batteries
>non proprietary, maybe some other vendor has a UPS design that puts a direct
>monitoring circuit on each individual 12V brick battery, thus avoiding the
>overheating problem I have described?
>
>Any information on why this overheating takes place, how to avoid it, and
>any referrals to third party UPS products that employ a more robust design
>are appreciated.

Roy L. Fuchs

2006-06-03, 4:21 am

On Sat, 03 Jun 2006 16:51:18 +1000, Peter Dettmann
<peter@aardvark.net.au> Gave us:

>On Wed, 31 May 2006 21:45:02 -0700, "Will" <westes-usc@noemail.nospam>
>wrote:
>
>You also have probelms keeping your posts just to appropriate news
>groups. SPAM is what is is.
>
>Peter Dettmann

Yet your retarded XXX had to quote and repost the entire chunk of
crap again.

You TOFUd it too.

Looks like you need to learn a few things about Usenet as well.

http://en.wikipedia.org/wiki/Top-posting

nicksanspam@ece.villanova.edu

2006-06-03, 5:21 am

William P.N. Smith <news2006c@compusmiths.com> wrote:
>nicksanspam@ece.villanova.edu wrote:
>
>But the meltdown doesn't come from charging current, it comes from
>internal shorting of a cell quickly converting all it's stored energy
>to heat.

I doubt that.

Nick

William P.N. Smith

2006-06-03, 8:21 am

Peter Dettmann <peter@aardvark.net.au> top-posted:
>You also have probelms keeping your posts just to appropriate news
>groups. SPAM is what is is.

Oh, I dunno, I invited him over to alt.energy.homepower from the
battery newsgroup, as there are a lot more people here with battery
experience. He might have ranged a bit wider than I would have, but
it's certainly marginally on-topic for these groups.

And SPAM is unsolicited commercial advertising, which I don't see any
of here. If you don't like the thread, click that little "ignore
thread" button underneath where it says "Tools".

Eric Sears

2006-06-03, 9:21 am

On Fri, 02 Jun 2006 09:24:51 +0800, budgie <me@privacy.net> wrote:

>On Thu, 01 Jun 2006 19:58:26 GMT, phoneme@025379386.for.email.address (Eric
>Sears) wrote:
>
>
>(snip)
>
>???? a 3000VA inverter is going to want 250A @12V input, assuming 100%
>efficiency. There IS a reason why higher input voltages are used as the output
>rating climbs. Even my 1000VA unit runs a 60V string of 5*12V.

I absolutely agree.
However, since the originator of this thread wanted something that was
easier to "fail-proof" I thought that less cells might be better (even
if larger amperage capacity).
My 350 watt UPS has a single 12v/6ah battery - which I guess means
that at full power it might draw 30 amps (not for long!). So maybe I
should have said about 50 ah for 3kw if scaled correctly.

But you are correct about input power. I suppose that most UPS's have
the "inverter" part running in sync with the grid power all the time,
and the battery only gets called on when the grid fails.

Perhaps a standard 48v inverter would be better, but then there is the
problem of "all those cells".

I guess in the end, as others have said, the best system is a regular
maintenance schedule of replacing batteries at a set time period.
If the regular batteries in the UPS were re-sited OUTSIDE the box, it
might be possible to a) prevent the heat from one battery affecting
the adjacent ones and b) monitor the individual battery voltages more
easily.

Thanks for your comments budgie.

Eric Sears.

JoeSP

2006-06-03, 9:21 am

<nicksanspam@ece.villanova.edu> wrote in message
news:e5rd77$968@acadia.ece.villanova.edu...
> William P.N. Smith <news2006c@compusmiths.com> wrote:
>
> I doubt that.
>
> Nick
>

LOL

JoeSP

2006-06-03, 9:21 am

"Will" <westes-usc@noemail.nospam> wrote in message
news:uOadnXKW3vt9Jx3ZnZ2dnUVZ_sidnZ2d@giganews.com...
> "William P.N. Smith" <news2006c@compusmiths.com> wrote in message
> news:8oa082laev3l0g698qa28gr212uk519k69@4ax.com...
>
> When testing batteries, is there some key sign that might disclose
> imminent
> failure of one of the 12V bricks? Would we for example see the voltage
> decline in a non-linear way as it declines from 12V to 10V?
>
> --
> Will
>

Our organization has opted for the simplest solution I can think of. Two
UPS's, one backing up the line, and the other backing up the first. They are
made of 10 gel cells each, inverted to AC without the need of a step-up
transformer. For long power failures, when one cuts out, the other one
takes over, to give us well over 4 hours of backup power. It also gives us
the redundancy of having two systems that won't fail at the same time. A
warning beep alerts us when the battery is no longer taking a proper charge
and needs to be replaced.

JoeSP

2006-06-03, 9:21 am

"jk" <klessig@cox.net> wrote in message
news:ts9182d3h3fbvd7idhr3fa4k6leqka5dfn@4ax.com...
> "Will" <westes-usc@noemail.nospam> wrote:
>
>
>
> IN both charge and discharge, this is true
> THe same current flows through both.
>
>
>
> What you want here is not that (Separate chargers for each battery
> gets expensive) but a cell/ battery monitor system. Such as Cell
> watch, or Alber.
>
> "Real" ups systems use them all the time.
> jk

Back in the days when batteries were mostly considered a power source, and
ran 36 VDC lights and appliances, charged by a donkey engine or a
windcharger, it was part of regular maintenance to test each 2V glass-jar
cell with a hydrometer and an ammeter. When one was faulty, you simply
unbolted the lead bars, inspected the lead plates for sulfation and erosion,
replaced the electrolyte, cleaned the plates, and you were back in business.

no one that you know

2006-06-03, 11:21 am

Have ya tried Alpha UPS?
I maintain about 590 of them all with three 12volt batts each.

Will wrote:

> Our company has had a long-standing problem where UPS batteries will at
> various points in their lifetime suddenly overheat, sometimes
> catastrophically to the point where the battery casing starts to melt and
> you can actually smell the gases from the battery leaking. So far we have
> been lucky to catch such thermal events with temperature sensors but it has
> always been a goal of mine to better understand why this happens, and to
> find some UPS system where it can be avoided entirely. To date, we have
> seen these problems with APC Symmetra tower, Symmetra rackmount, and
> SmartUPS.
>
> After working with an electrician, I have a theory about why this is
> happening, and if correct, the theory suggests a different design for UPS
> systems that would avoid the problem. I am hoping some manufacturer has
> already implemented this idea and someone can refer me to their products.
>
> On all of the UPS systems we use generic "brick" batteries are joined
> together in a series, then the leads from the ends of these battery chains
> are connected to the UPS. The problem is that batteries rarely fail all
> together. If a 12V battery should be considered discharged and not useful
> at around 10V, and you have two 12V batteries joined in series, what happens
> when one of the batteries maintains a full charge at 12V but the other
> battery in the series starts to lose its ability to hold charge and slips
> below some critical level? From the point of view of the UPS, it
> doesn't see anything about the state of individual batteries. The UPS only
> sees that the total voltage of the two 12V batteries in series has fallen
> from 24V to 22V.
>
> Maybe an electrical engineer can step in here and explain what is happening,
> but my pure guess is that to maintain the same power output, an increased
> amount of current probably has to flow through the batteries. That
> creates problems with heating for the "good" battery, which is still
> measuring 12V. Now that 12V is receiving too much current, overcharges,
> overheats, and at some point the casing of the battery starts to melt. I
> haven't done enough experimentation to determine if it is the good battery
> or bad battery that is overheating. To be honest, in such situations I
> have often seen evidence that both batteries start to melt. Perhaps this
> is nothing more than one battery being in physical proximity to the
> overheating battery and therefore gaining heat from its physical contact.
> The only thing that is common to all cases is that one of the two batteries
> has discharged and should have been replaced before the overheating event
> took place.
>
> Regardless of the actual mechanism for the overheating we are observing, it
> seems to me that the obvious solution is to design UPS systems to physically
> connect to each 12V battery individually. Forget connecting multiple
> batteries in series, at least don't do that at the battery itself. By
> connecting to and monitoring individual batteries, now the UPS can see when
> an individual battery falls below some critical voltage threshold and put it
> into a special recharge state (not put any load on it). If the battery
> fails to recharge, the UPS can declare the battery defective and can signal
> the condition by an LED on the battery's compartment. If there is a
> network attached monitoring system, the UPS can send an e-mail.
>
> Aside from increasing safety and utility of the monitoring system, such a
> design would allow much easier re-use of off-the-shelf batteries, improving
> ease-of-use in making battery changes and lowering cost. While I realize
> that APC in particular has no desire to make anything regarding batteries
> non proprietary, maybe some other vendor has a UPS design that puts a direct
> monitoring circuit on each individual 12V brick battery, thus avoiding the
> overheating problem I have described?
>
> Any information on why this overheating takes place, how to avoid it, and
> any referrals to third party UPS products that employ a more robust design
> are appreciated.
>
> --
> Will