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Home > Archive > Electrical Engineering > April 2006 > lead acid batteries in parallell?
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lead acid batteries in parallell?
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| Frank White 2006-04-07, 2:21 pm |
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I have seen this a few times now and have always felt that it is a bad
idea because if one cell in one of the batteries is worn out more than
the others then you will always be discharging one battery with the
other.
The first time I saw this was on tractor starting batteries, and
recently on a scissorlift.
How common are parallell battery arrangements and is this something
worth worrying about?
Remove dashes "-----------" to e-mail.
delik2-------------@shaw.ca
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| Frank White wrote:
> I have seen this a few times now and have always felt that it is a bad
> idea because if one cell in one of the batteries is worn out more than
> the others then you will always be discharging one battery with the
> other.
>
> The first time I saw this was on tractor starting batteries, and
> recently on a scissorlift.
> How common are parallell battery arrangements and is this something
> worth worrying about?
>
>
> Remove dashes "-----------" to e-mail.
>
> delik2-------------@shaw.ca
Parallel batteries are very common on cruising boats (usually under 50
feet in length). Faulty cells as you describe are uncommon except toward
the end of the useful life of the batteries.
The general rule for paralleling batteries is that the batteries should
be of the same make, type, size, and age.
Good luck.
Chuck
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| Floyd L. Davidson 2006-04-07, 9:21 pm |
| chuck <nospam@nospam.net> wrote:
>Frank White wrote:
>
>Parallel batteries are very common on cruising boats (usually
>under 50 feet in length). Faulty cells as you describe are
>uncommon except toward the end of the useful life of the
>batteries.
>
>The general rule for paralleling batteries is that the batteries
>should be of the same make, type, size, and age.
I've seen 48 VDC battery plants in telephone offices with 3 and
4 different strings in parallel. They might be described as
relatively similar in type, somewhat similar in size, and very
different in age and make.
The point of similarity is necessarily the voltage ratings,
which essentially means they all must be able to operate with
the same charge voltage, the same float voltage, the same cutoff
voltages, etc. etc.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
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| Rich256 2006-04-07, 11:21 pm |
| Floyd L. Davidson wrote:
> chuck <nospam@nospam.net> wrote:
>
> I've seen 48 VDC battery plants in telephone offices with 3 and
> 4 different strings in parallel. They might be described as
> relatively similar in type, somewhat similar in size, and very
> different in age and make.
>
> The point of similarity is necessarily the voltage ratings,
> which essentially means they all must be able to operate with
> the same charge voltage, the same float voltage, the same cutoff
> voltages, etc. etc.
>
Unless one has a shorted cell there should be no problem in parallel.
My Diesel Truck has parallel batteries.
It appears to me that if they are not the same size the one with the
larger capacity will supply most of the current. Since the voltage will
always be equal they should discharge to the same state of charge even
though they are different size.
When being charged they will charge according to their size, the voltage
determining their state of charge.
| |
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| Rich256 wrote:
> Floyd L. Davidson wrote:
>
>
>
> Unless one has a shorted cell there should be no problem in parallel. My
> Diesel Truck has parallel batteries.
>
>
> It appears to me that if they are not the same size the one with the
> larger capacity will supply most of the current. Since the voltage will
> always be equal they should discharge to the same state of charge even
> though they are different size.
>
> When being charged they will charge according to their size, the voltage
> determining their state of charge.
Just to make sure we're all on the same wavelength, I agree that there
will probably be no explosions or meltdowns if one connects two
different batteries (of the same voltage) in parallel.
However, if for example one of these is a conventional lead-acid type
and the other is an AGM type, or if one is new and the other is near the
end of its life (i.e., with high internal resistance) then connecting
them in parallel will not be nearly as satisfactory as had both
batteries been similar. Can it be done? Sure. We've all done it when
necessary. But is it a good design practice? I don't think so.
If the OP were technically able to determine that the relevant
characteristics of the batteries being considered make them good
candidates for paralleling, then what was the purpose of the original post?
Telephone company batteries tend to differ from automotive type
batteries. They are usually monitored closely and systematically by
trained personnel.
Chuck
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| Spokesman 2006-04-08, 1:21 pm |
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"Frank White" <delik2----------------@shaw.ca> wrote in message
news:hf6d32t68mk3ppf3n5f991sdksajhjbb13@4ax.com...
>
> I have seen this a few times now and have always felt that it is a bad
> idea because if one cell in one of the batteries is worn out more than
> the others then you will always be discharging one battery with the
> other.
>
> The first time I saw this was on tractor starting batteries, and
> recently on a scissorlift.
> How common are parallell battery arrangements and is this something
> worth worrying about?
Most emergency light systems that supply more than two or three remote
units use multiple series/parrallel batteries. If they are allowed in
this
application they must be quite reliable.
>
>
> Remove dashes "-----------" to e-mail.
>
> delik2-------------@shaw.ca
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| Pablo 2006-04-10, 10:21 am |
| US Navy submarines have been using batteries in parallel for decades...same
aH, rating, no problem !!
"Frank White" <delik2----------------@shaw.ca> wrote in message
news:hf6d32t68mk3ppf3n5f991sdksajhjbb13@4ax.com...
>
> I have seen this a few times now and have always felt that it is a bad
> idea because if one cell in one of the batteries is worn out more than
> the others then you will always be discharging one battery with the
> other.
>
> The first time I saw this was on tractor starting batteries, and
> recently on a scissorlift.
> How common are parallell battery arrangements and is this something
> worth worrying about?
>
>
> Remove dashes "-----------" to e-mail.
>
> delik2-------------@shaw.ca
>
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| daestrom 2006-04-10, 6:21 pm |
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"Pablo" <sertec@snet.net> wrote in message
news:nxs_f.9413$%m4.321@newssvr33.news.prodigy.com...
> US Navy submarines have been using batteries in parallel for
> decades...same aH, rating, no problem !!
>
BULL!!! Want to tell me were on a submarine you think the lead acid
batteries are in parallel?? Battle-lanterns (6V primary cells that are
never recharged) ??
Nuc boats only have one ships battery and it's over a hundred cells in
series. Diesel boats (of which the US Navy has zero) had two ships
batteries. Yes, those could be connected in parallel, but only during
discharge, they charge separately (various connections could be set up from
the manuevering room)
Parallel operation can work well for small batteries like your typical
marine engine starting application. But it isn't the best choice. One
battery can go bad and 'hog' all the charging current. Many marine
applications include a switch to allow switching from one battery, to the
other, both, or neither (nice to be able to disconnect the batteries when
working in the engine compartment)
daestrom
(former Chief Electrican's Mate, USNavy Submarine Service)
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| Ross Mac 2006-04-13, 10:21 pm |
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"Frank White" <delik2----------------@shaw.ca> wrote in message
news:hf6d32t68mk3ppf3n5f991sdksajhjbb13@4ax.com...
>
> I have seen this a few times now and have always felt that it is a bad
> idea because if one cell in one of the batteries is worn out more than
> the others then you will always be discharging one battery with the
> other.
>
> The first time I saw this was on tractor starting batteries, and
> recently on a scissorlift.
> How common are parallell battery arrangements and is this something
> worth worrying about?
>
>
> Remove dashes "-----------" to e-mail.
>
> delik2-------------@shaw.ca
Should work fine as long as you use the proper isolation system. Here's one
link of many that explains it in the event you don't already know of such
devices..
http://www.thejump.net/fishingarticles/Ship-Shape.htm
Good luck....Ross
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