It's perfectly okay to parallel large batteries, with one important
caveat: They should be identical in every way, preferably from the same
lot number. Most large uninterruptible power systems use series-parallel
strings of batteries, with very high reliability. I oversee the operation
of two 50 kVA UPSs where I work, and each of them has two strings of 40
sealed lead-acid batteries in parallel. That's about 550 VDC per string,
and represents a very large energy source. When these batteries reached
four years of age, all 160 batteries were replaced at one time, and all
were from the same lot.
This is critical when you have only two 12 VDC batteries in parallel.
Even if you had two batteries with the same part number, but one was a few
months older than the other, the internal resistances and charge/discharge
characteristics will not match- and one battery will carry significantly
more load than the other. Don't even think about paralleling two
different brands or sizes of batteries!
73, Eric Lemmon WB6FLY
goodyk3ng wrote:
> Greetings,
>
> I'm curious if anyone has experience paralleling deep cycle batteries
> for a repeater backup. I'm designing a battery disconnect circuit
> that will open a relay if it detects over voltage, or if the
> batteries discharge to a low voltage threshold. I'm also going to
> liberally fuse everything. Float voltage will be provided by a
> modified Astron 50 Amp supply.
>
> I'm aware of the math to determine backup time and the care and
> feeding of lead acid batteries, but I have a concern with paralleling
> multiple batteries. I'm worried that if we have one battery go soft,
> it will draw current and eventually boil off its electrolyte or worse,
> overheat.
>
> Can anyone relay any real life experiences with this?
>
> Thanks and 73
> Goody
> K3NG
>
>
> Yahoo! Groups Links
>
>
>
>
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