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| Author |
DC power for communications site
|
|
|
| Greetings,
I am involved with an application where we will have communication
cabinets or shelters located in remote locations, but most have
electric service available. However some may not be accessible for
days depending on weather. All of the equipment will run on -48VDC os
there is no UPS. A rectifier shelf supplied with 240VAC will provide
the -48VDC thru a distribution panel (DC circuit breakers) which will
power the equipment as well as charge backup batteries. One vendor has
suggested that the batteries would be one load on the distribution
shelf and the equipment would be the other. Then when the rectifiers
go down due to an outage the equipment would be backfed thru the
distribution panel. I have not worked with DC power systems but from
working with AC power it doesn't seem kosher to backfeed thru a panel.
I am hoping that one of you could provide a schematic or system
description for this type application.
Secondly, since the sites are remote we would like to have remotely
resetable breakers in the distribution panel. We have remote ability
to provide contact closures or toggle control voltages as well as read
voltage and current.
Looking forward to your comments.
Thanks,
jh
| |
| John Gilmer 2007-10-17, 8:25 pm |
| It's been "awhile" but in the Old Bell System the offices all ran from 48
volt batteries that were always being charged.
During "normal" periods when AC power was available, there was a
compensation cell is series with the 48 volt battery than dropped the actual
voltage when being charged back down to the 48 volt range.
When "main" power went down a relay shorted out the compensation cell.
Frankly, that's looks like a good system for your application.
Just have your stuff run from battery all the time and as alternative power
is available you charge the battery. The "compensation cell" may not be
worth the trouble.
The Old Bell System tended to go first class with the batteries. They were
kept well away from the various relay racks and distribution frames so that
there would not be any contamination problems. Several hundred sqare feet
of floor space was for the batteries.
"jvh" <johnvhite@texoma.net> wrote in message
news:1192646913.751594.58460@t8g2000prg.googlegroups.com...
> Greetings,
>
> I am involved with an application where we will have communication
> cabinets or shelters located in remote locations, but most have
> electric service available. However some may not be accessible for
> days depending on weather. All of the equipment will run on -48VDC os
> there is no UPS. A rectifier shelf supplied with 240VAC will provide
> the -48VDC thru a distribution panel (DC circuit breakers) which will
> power the equipment as well as charge backup batteries. One vendor has
> suggested that the batteries would be one load on the distribution
> shelf and the equipment would be the other. Then when the rectifiers
> go down due to an outage the equipment would be backfed thru the
> distribution panel. I have not worked with DC power systems but from
> working with AC power it doesn't seem kosher to backfeed thru a panel.
> I am hoping that one of you could provide a schematic or system
> description for this type application.
>
> Secondly, since the sites are remote we would like to have remotely
> resetable breakers in the distribution panel. We have remote ability
> to provide contact closures or toggle control voltages as well as read
> voltage and current.
>
> Looking forward to your comments.
>
> Thanks,
>
> jh
>
| |
| Tim Perry 2007-10-18, 9:25 am |
|
"jvh" <johnvhite@texoma.net> wrote in message
news:1192646913.751594.58460@t8g2000prg.googlegroups.com...
> Greetings,
>
> I am involved with an application where we will have communication
> cabinets or shelters located in remote locations, but most have
> electric service available. However some may not be accessible for
> days depending on weather. All of the equipment will run on -48VDC os
> there is no UPS. A rectifier shelf supplied with 240VAC will provide
> the -48VDC thru a distribution panel (DC circuit breakers) which will
> power the equipment as well as charge backup batteries. One vendor has
> suggested that the batteries would be one load on the distribution
> shelf and the equipment would be the other. Then when the rectifiers
> go down due to an outage the equipment would be backfed thru the
> distribution panel. I have not worked with DC power systems but from
> working with AC power it doesn't seem kosher to backfeed thru a panel.
> I am hoping that one of you could provide a schematic or system
> description for this type application.
In effect it is a UPS, just not the kind you are used to seeing.
If I interpret your post correctly all the equipment will run on an
appropriatly sized DC power supply.
A backup battery bank is then being charged by an appropriatly sized
maintance charger.
The usual practice is to 'float' the backup batteries by connecting then to
the load through a diode which prevents the main supply from overcharging
them.
>
> Secondly, since the sites are remote we would like to have remotely
> resetable breakers in the distribution panel.
Remote breaker reseting should be done with a great deal of consideration.
How likely witll the result be a fire? How much damage will result by
forcing a reset to a shorted power supply?
An anaogy would be: the guy that repeatedly resets the CB to the garage with
out fixing the fault until the garage burns down.
> We have remote ability
> to provide contact closures or toggle control voltages as well as read
> voltage and current.
>
> Looking forward to your comments.
>
> Thanks,
>
> jh
| |
|
| Thanks for the posts gentlemen.
Yes we are in some ways simulating a UPS and in fact life would be
easier if all the equipment ran on 120VAC. But I didn't get a choice.
However, there may be a chance to kill two rats with one rock here
(used to say 'kill 2 birds...' until we started keeping pet birds).
The diode could protect the battery bank from overcharge and at the
same time provide a little voltage drop. We don't have a final spec on
the tolerance allowed for the -48VDC but four fully charged batteries
in series would provide 52.8 VDC.
The remote reset will be a remote 'manual' operation if I may use such
a term. We have monitoring equipment that can read current and voltage
and the readings are recorded on a periodic (period TBD) basis. When
the breaker is reset we will take readings in a tight loop for a
period of time and if the load remains normal will look for signs of
transients. I am a engineer by degree but have been a software weenie
for 20+ years but I will be reluctant to go along with automating this
process. Perhaps a line voltage monitor would be appropriate so we
could detect incoming transients. However there is pressure to keep
the instrument count down. One for cost purposes, two, more components
reduce MTBF.
Any recommendations for DC power shelf vendors?
Best Regards,
John
| |
|
| I should add that we have found some remotely controlled PDUs, one
source is specpower.com. Still looking for others as well as power
shelves.
jh
| |
| Michael A. Terrell 2007-10-18, 9:25 am |
| John Gilmer wrote:
>
> It's been "awhile" but in the Old Bell System the offices all ran from 48
> volt batteries that were always being charged.
>
> During "normal" periods when AC power was available, there was a
> compensation cell is series with the 48 volt battery than dropped the actual
> voltage when being charged back down to the 48 volt range.
>
> When "main" power went down a relay shorted out the compensation cell.
Bullshit. No one in their right mind would 'Short out' a high
capacity lead acid battery.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
| Floyd L. Davidson 2007-10-18, 1:25 pm |
| jvh <johnvhite@texoma.net> wrote:
>Thanks for the posts gentlemen.
>
>Yes we are in some ways simulating a UPS and in fact life would be
>easier if all the equipment ran on 120VAC. But I didn't get a choice.
The choice of 48 VDC is a good one.
I worked in telecommunications equipment rooms, all of
which were powered by 48 volt battery plants, so I admit
to being habituated. That included hands on experience
with dozens of installations that match what you have
described, ranging in size from the Fairbanks Toll
Center to small satellite stations that fit into one
rack.
Many of these sites handle either FAA circuits or DoD
circuits that require immediate response, and the cost
of putting a craftperson on site exceeded $2000 just for
the aircraft. Reliability is the top priority.
>However, there may be a chance to kill two rats with one rock here
>(used to say 'kill 2 birds...' until we started keeping pet birds).
>The diode could protect the battery bank from overcharge and at the
There is no diode, as such.
>same time provide a little voltage drop. We don't have a final spec on
>the tolerance allowed for the -48VDC but four fully charged batteries
>in series would provide 52.8 VDC.
The "correct" float voltage is specified by the
manufacturer of the batteries.
The voltages of interest are the "high voltage cutoff"
(and you want a separate circuit that will shutdown the
plant if that voltage is exceeded), the "charge
voltage", the "float voltage", and the "low voltage
cutoff" (which like the maximum voltage, should have a
separate detection circuit to disconnect the batteries
from any load when this voltage is reached).
Normal operation, when AC is available, will be at the
float voltage (roughly 52-54 volts). If you place the
plant on "charge", to equalize the cells (for example
that should always be done if water is added to any
cell), the regulator should adjust the voltage to the
"charge voltage" (about 56 volts, which like the float
voltage depends on the specific batteries used).
If AC power is lost, the battery begins to discharge.
There *absolutely* *must* be a low voltage disconnect
(which will operate at about 42 volts), or your
batteries will be destroyed by an extended power
failure.
As has been mentioned, in "the good old day" there was
also usually some sort of a device to reduce the
operating bus voltage when the plant was floating. CEMF
cells and other devices were common. That is much less
common today than it once was.
For most relatively small installations today, gel cells
rather than wet cells, are preferred.
>The remote reset will be a remote 'manual' operation if I may use such
>a term. We have monitoring equipment that can read current and voltage
>and the readings are recorded on a periodic (period TBD) basis. When
>the breaker is reset we will take readings in a tight loop for a
>period of time and if the load remains normal will look for signs of
>transients. I am a engineer by degree but have been a software weenie
>for 20+ years but I will be reluctant to go along with automating this
>process. Perhaps a line voltage monitor would be appropriate so we
>could detect incoming transients. However there is pressure to keep
>the instrument count down. One for cost purposes, two, more components
>reduce MTBF.
I've never seen any of that sort of equipment used...
Take that as a recommendation to assume it isn't needed!
On the other hand, a single telephone line provided by
the closest thing to "diversity" that is possible,
connected to equipment that can power cycle and/or do
software resets on as many other equipments as possible
is *definitely* a money making asset. Ideally that
would be included as part of the alarm system.
Also, the typical configuration for a small installation
such as you've described, is to have a redundant pair of
regulators, each of which is large enough to handle the
load without the other. Typically they are operated in
parallel, each with about half the normal load.
With larger installations the number of charging units
operated in parallel is greater than two, even if the
capacity of each is also increased. The design target
then would be that the maximum charge rate (to recover
from a discharge down to the low voltage cutoff, for
example) would require all chargers to be active.
>Any recommendations for DC power shelf vendors?
I can only remember two manufacturers... WECo (AT&T in
the old days) and Lorain Power Systems.
Certainly there must be others, but Lorain comes *very*
highly recommended.
Oh, incidentally... a little DC-AC inverter unit can
provide 120VAC for the few things that require protected
AC power.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
|
| On Oct 18, 10:11 am, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:
> John Gilmer wrote:
>
>
>
>
> Bullshit. No one in their right mind would 'Short out' a high
> capacity lead acid battery.
>
Good catch. A curiosity now, a break before make double throw would
cause a dropout. Seems like the comp cell should be ahead of the load
so maybe there was a diode in series between charger and the comp cell
to only allow current to flow thru it backwards. Then I think the
relay could bypass the comp cell. However it seems this would over
charge the comp cell on a regular basis.
jh
| |
| Floyd L. Davidson 2007-10-18, 1:25 pm |
| "Michael A. Terrell" <mike.terrell@earthlink.net> wrote:
>John Gilmer wrote:
>
> Bullshit. No one in their right mind would 'Short out' a high
>capacity lead acid battery.
Nope, not bullshit. He's *precisely* correct.
A "compensation cell" is in *no* *way* anything that
would be described as "a high capacity lead acid
battery". CEMF cells (an alkaline cell with nickle
electrodes), resistors, diodes, and probably 3 devices
that I can't remember, have all been used as the
"compensation cell", and virtually any of them can be
directly shorted.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
|
| Great post Floyd, a lot of good info which generate more questions.
>
> There is no diode, as such.
>
Pardon my density, I wish I had a schematic of your connections. It
sounds like the batteries were being charged by the same source as
feeds the load. If that is the case we will be drawing about 30 amps
on an continuous basis. If the battery and the equipment load are in
parallel how are the batteries maintained at float?
>
> If AC power is lost, the battery begins to discharge.
> There *absolutely* *must* be a low voltage disconnect
> (which will operate at about 42 volts), or your
> batteries will be destroyed by an extended power
> failure.
>
Correct my PDU has an LVD and an OVD.
> As has been mentioned, in "the good old day" there was
> also usually some sort of a device to reduce the
> operating bus voltage when the plant was floating. CEMF
> cells and other devices were common. That is much less
> common today than it once was.
>
Not familiar with off the shelf CEMF devices. Will have to surf.
> For most relatively small installations today, gel cells
> rather than wet cells, are preferred.
>
I have heard this b4. Is it because they don't vent and de-hydrate?
>
> I've never seen any of that sort of equipment used...
> Take that as a recommendation to assume it isn't needed!
>
> On the other hand, a single telephone line provided by
> the closest thing to "diversity" that is possible,
> connected to equipment that can power cycle and/or do
> software resets on as many other equipments as possible
> is *definitely* a money making asset. Ideally that
> would be included as part of the alarm system.
>
Actually will have customer edge routers on VPNs on redundant lines
provided by a major telco. Attached to the routers will have an SNMP
device that has analog inputs, relay contacts, as well as digital I/O.
Monitoring is dictated so I have no choice tho I agree that we are
adding complexity and reducing reliability at the same time.
> Also, the typical configuration for a small installation
> such as you've described, is to have a redundant pair of
> regulators, each of which is large enough to handle the
> load without the other. Typically they are operated in
> parallel, each with about half the normal load.
>
Pretty much all the equipment is redundant, including battery racks.
>
> I can only remember two manufacturers... WECo (AT&T in
> the old days) and Lorain Power Systems.
>
Thanks,
jh
| |
| Floyd L. Davidson 2007-10-18, 1:25 pm |
| jvh <johnvhite@texoma.net> wrote:
>On Oct 18, 10:11 am, "Michael A. Terrell" <mike.terr...@earthlink.net>
>wrote:
>
>Good catch.
Except he's dead wrong.
>A curiosity now, a break before make double throw would
>cause a dropout. Seems like the comp cell should be ahead of the load
>so maybe there was a diode in series between charger and the comp cell
>to only allow current to flow thru it backwards. Then I think the
>relay could bypass the comp cell. However it seems this would over
>charge the comp cell on a regular basis.
The "comp cell" holds *no* charge. That is why it can
be shorted. It merely provides a voltage drop that is
essentially independent of the current.
The original "comp cell" was a CEMF (Counter EMF) cell
that used nickel electrodes immersed in an alkaline
solution. Because it gassed at a very high rate the
electrolyte solution had half an inch or so of mineral
oil floating on top.
The drop across a CEMF cell was just over 2 volts, and
if provisioned in two arrays of multiple cells in
parallel (to handle the current) would allow for just
over 4 volts of voltage adjustment in two steps of 2
volts each.
An interesting story... In the late 70's I worked at a
troposcatter communications site (which had WECO battery
plant equipment) that was about to be replaced with one
of those new fangled satellite earth stations (all of
which used Lorain power equipment). When this story
actually started, we knew it would eventually happen,
but weren't sure when.
The battery plants where stacked against a wall, three
cells high on steel racks. The top would have been at
about 11 feet off the floor. The large 130 volt supply
cells were on the upper tier. There was a small window
just above the level of the cable racks (at 11 feet off
the floor), and in the spring the sun would shine
through the windows onto the top tier of batteries for a
few hours each day. And it had been doing that for 20
years.
So one day we discovered that a battery on the top tier,
directly above the CEMF cells on the bottom tier, had
cracked. There was acid all over the wall, all over the
cells below it, into the CEMF cells, and about 1/4 inch
of acid on the floor for about 12-15 feet in every
direction. (This is the worst nightmare you can imagine
for someone doing "station checks"! It's a really bad
bad-hair day after that.)
Cleaning that up was a huge job. The tiles on the floor
had to be replaced. The wall and the steel racks were
never the same. The CEMF cells had to be totally
rebuilt, after emptying them, scrubbing them out and
putting in new electrolyte and mineral oil, they were
like new.
And I wish I could tell you we had used our heads, but
we did all that by rote and by note, and totally
*missed* the important point. Which was that there were
two other cells that had had the sun shining on them for
20 years!
So the next spring, *another* cell cracks and we finally
do see the light. That window got blocked off!
But by that time we also had an exact date for when
everything was going to be turned down, and we just
couldn't see all that work going into something that
would be shutdown in 14 months. So we did only the
minimum. We left those CEMF cells exactly as they were,
figuring that if they actually failed we'd do whatever
it took.
They didn't fail; the electrolyte turned green. They
grew stuff inside the cells, it looked unbelievably
ugly. But they kept right on ticking until the day
everything was turned off.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Stuart 2007-10-18, 5:25 pm |
| In article <1192709417.069476.66940@z24g2000prh.googlegroups.com>,
jvh <johnvhite@texoma.net> wrote:
> We don't have a final spec on
> the tolerance allowed for the -48VDC but four fully charged batteries
> in series would provide 52.8 VDC.
This is normal and allowed for in the spec for 48V DC operated comms
equipment.
--
Stuart Winsor
From is valid but subject to change without notice if it gets spammed.
For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk
| |
| Stuart 2007-10-18, 5:25 pm |
| In article <47173e22$0$32564$4c368faf@roadrunner.com>,
Tim Perry <timperry@nospammeadelphia.net> wrote:
> The usual practice is to 'float' the backup batteries by connecting then
> to the load through a diode which prevents the main supply from
> overcharging them.
Not entirely sure what you mean by this.
Modern chargers designed for this application are constant voltage and the
load and the charger are connected to the battery at the same point
--
Stuart Winsor
From is valid but subject to change without notice if it gets spammed.
For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk
| |
| Stuart 2007-10-18, 5:25 pm |
| In article <1192725155.230091.166500@t8g2000prg.googlegroups.com>,
jvh <johnvhite@texoma.net> wrote:
> If that is the case we will be drawing about 30 amps
> on an continuous basis. If the battery and the equipment load are in
> parallel how are the batteries maintained at float?
The charger is rated according to the load you are supplying. I have
several in by shed but I cannot get at them at the moment to comfirm the
amperage rating but it is quite high. They are switch mode devices.
--
Stuart Winsor
From is valid but subject to change without notice if it gets spammed.
For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk
| |
| Floyd L. Davidson 2007-10-18, 5:25 pm |
| jvh <johnvhite@texoma.net> wrote:
>Great post Floyd, a lot of good info which generate more questions.
>
>Pardon my density, I wish I had a schematic of your connections. It
>sounds like the batteries were being charged by the same source as
>feeds the load. If that is the case we will be drawing about 30 amps
>on an continuous basis. If the battery and the equipment load are in
>parallel how are the batteries maintained at float?
When AC power is present, the charge circuit regulates
the voltage at the "float voltage" specified for the
batteries. At that voltage the batteries are taking a
charge, though it is relatively small. Hence the
battery is just part of the load as far as the AC
charging equipment is concerned.
If the AC fails, then the battery supplies power to the
load, but it will be at a lower voltage. Typically the
float voltage would be about 53 volts, and the battery
itself would be 48 volts when fully charge, dropping
down to 42 volts before a low voltage cutout prevents a
total discharge (which would destroy the battery cells).
The battery is always connected. It has, in addition to
stored energy, the attribute of being a wonderful filter
too.
In fact, you can visualize the whole thing as if the
battery itself is just a really big capacitor with
fairly high leakage. If the AC power is disconnected
the load is supplied from the charge in the capacitor
until it is drained. The only difference is that a
battery has a much larger stored charge, so it takes
much longer to discharge it.
....
>Not familiar with off the shelf CEMF devices. Will have to surf.
Horrible things, that you don't want to use!
>I have heard this b4. Is it because they don't vent and de-hydrate?
That is probably the main attraction. Maintenance free is
a good policy for unmanned sites... :-)
>
>Actually will have customer edge routers on VPNs on redundant lines
>provided by a major telco. Attached to the routers will have an SNMP
>device that has analog inputs, relay contacts, as well as digital I/O.
>Monitoring is dictated so I have no choice tho I agree that we are
>adding complexity and reducing reliability at the same time.
As long as the "SNMP device" can be accessed via either
of the redundant lines, that appears to fit the bill.
Monitoring shouldn't actually reduce reliability. Alarm
systems are a bit of a black art though, and it's really
difficult to see the potentials until there is some
actual operating experience. Six months before
installation the poor design engineer just isn't going
to know all the "interesting" things that operations
will be able to tell him he did wrong, after they've
used it for a couple years!
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Phillip Devoll 2007-10-18, 8:25 pm |
| my brother works on these type of setups..... the chargers and the
batterys and the phone system are all in parellel
if the phone system draws 100 amps at 48 volts dc then they will have 3 of 4
chargers in parallel so that the batterys can charge if they run completly
dead and so they won't trip the charger offline..... and redundinacy if one
of the chargers fail the rest of the units will not trip offline...
"Tim Perry" <timperry@nospammeadelphia.net> wrote in message
news:47173e22$0$32564$4c368faf@roadrunner.com...
>
> "jvh" <johnvhite@texoma.net> wrote in message
> news:1192646913.751594.58460@t8g2000prg.googlegroups.com...
>
> In effect it is a UPS, just not the kind you are used to seeing.
>
> If I interpret your post correctly all the equipment will run on an
> appropriatly sized DC power supply.
>
> A backup battery bank is then being charged by an appropriatly sized
> maintance charger.
>
> The usual practice is to 'float' the backup batteries by connecting then
> to
> the load through a diode which prevents the main supply from overcharging
> them.
>
>
>
>
> Remote breaker reseting should be done with a great deal of consideration.
> How likely witll the result be a fire? How much damage will result by
> forcing a reset to a shorted power supply?
> An anaogy would be: the guy that repeatedly resets the CB to the garage
> with
> out fixing the fault until the garage burns down.
>
>
>
>
>
>
>
>
| |
| Tim Perry 2007-10-18, 9:25 pm |
|
"Stuart" <SW_NOSPAM@dsl.pipex.com> wrote in message
news:4f33da15e4SW_NOSPAM@dsl.pipex.com...
> In article <47173e22$0$32564$4c368faf@roadrunner.com>,
> Tim Perry <timperry@nospammeadelphia.net> wrote:
>
>
> Not entirely sure what you mean by this.
Some method of limiting charging current to a depleted battery bank while
simultaneously operating equipment when main power is restored. There are
probably several schemes to accomplish this.
My speculation is that load will have a high peak current at a low duty
cycle, something like a digipeater. I admit its just a guess but it would
probably need a high current regulated supply.
Some method of maintaining normal operation when the battery fails should be
included. (I have seen melted shorted gel cells)
Schemes to extend battery life by deep cycling them abound and could be
included as desired (and budget alows).
>
> Modern chargers designed for this application are constant voltage and the
> load and the charger are connected to the battery at the same point
It's simple easy and reliable but you have to assume supply current will not
exceed a value that will harm the batterys under max charge conditions and
you also have to assume the batterys will never short.
>
> --
> Stuart Winsor
>
> From is valid but subject to change without notice if it gets spammed.
>
> For Barn dances and folk evenings in the Coventry and Warwickshire area
> See: http://www.barndance.org.uk
| |
| Floyd L. Davidson 2007-10-18, 9:25 pm |
| "Tim Perry" <timperry@nospammeadelphia.net> wrote:
>"Stuart" <SW_NOSPAM@dsl.pipex.com> wrote in message
>news:4f33da15e4SW_NOSPAM@dsl.pipex.com...
>
>Some method of limiting charging current to a depleted battery bank while
>simultaneously operating equipment when main power is restored. There are
>probably several schemes to accomplish this.
It's fairly simple in practice. Each charging unit
(commonly called a "rectifier") has a current limiter,
and can only supply so much current. The voltage
regulation has to be common though, and in some way
shared by all of the charging units. That can be as
simple as the units sequentially come online and if a
given unit cannot regulate the voltage without exceeding
maximum current, it will go into current limiting and
pass voltage regulation to the next unit in the
sequence.
After an extended AC power outage it might well be that
for a short time all of the charging units will be in
current limiting. The voltage will slowly rise until it
reaches whatever is set for voltage regulation.
Generally the voltage will always be set to the float
voltage, and in an automatic mode the only variation
from that would be when all charging units are in
current limiting.
As the battery becomes charged the current it can take is
reduced. When it goes down sufficiently, the plant will
go into voltage regulation rather than current regulation.
However, it _is_ an interesting experience to watch a
large plant go through that cycle.
>My speculation is that load will have a high peak current at a low duty
>cycle, something like a digipeater. I admit its just a guess but it would
>probably need a high current regulated supply.
The instantaneous peak current requirements need only be
within the limits of the /batteries/, not the charging
mechanism. The charging mechanism need only be large
enough to handle the average load plus sufficient to
eventually recharge a discharged battery.
Of course generally the peak capacity of the charging
system is going to be high enough to recharge the
battery at the manufacturer's specified normal rate,
plus handle the highest "normal" load likely to be
encountered at the same time.
>Some method of maintaining normal operation when the battery fails should be
>included. (I have seen melted shorted gel cells)
That's provided by the Armstrong with Wrench method!
Unbolt any part of the series connections for the
battery, and everything runs on the charging units
instead of the battery plant. It works, but is not
without some consequence. The battery provides
filtering and voltage regulation, which ceases to exist.
Typically a higher level of power line hum will be
experienced without the battery.
>Schemes to extend battery life by deep cycling them abound and could be
>included as desired (and budget alows).
Beware of trying to homebrew such schemes!
The manufacturer of the batteries can provide detailed
information on a specific type of battery, and that is
what should be followed. There are distinctly
*different* instructions for virtually every battery
type, and just picking one off the wall is likely to
shorten battery life significantly.
>
>It's simple easy and reliable but you have to assume supply current will not
>exceed a value that will harm the batterys under max charge conditions and
>you also have to assume the batterys will never short.
Of course. But assuming the supply current is correct
is merely saying that the system is properly designed.
Batteries shorting is not exactly a common occurrence,
nor is it particularly exciting. Most telephone company
battery plants last for a couple of decades without
having any significant problems. Between 20 and 30
years they take a lot of babying, and how far they go
depends greatly on how well they were maintained in
those first 20 years.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| 54v_float 2007-10-19, 5:25 pm |
| The "compensation cell" is NOT a lead acid battery, typically it was a
selenium rectifier rated for the CHARGE current of the battery string.
Jim http://telco-power.com
also a DD214 holder.....
On Oct 18, 9:11 am, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:
>
> Bullshit. No one in their right mind would 'Short out' a high
> capacity lead acid battery.
>
> --
> Service to my country? Been there, Done that, and I've got my DD214 to
> prove it.
> Member of DAV #85.
>
> Michael A. Terrell
> Central Florida
| |
| 54v_float 2007-10-19, 5:25 pm |
| Http://telco-power.com
On Oct 18, 7:10 am, jvh <johnvh...@texoma.net> wrote:
> Thanks for the posts gentlemen.
>
> Any recommendations for DC power shelf vendors?
>
> Best Regards,
>
> John
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