Multiple SLA Batteries in Parallel

 

I have never been to this newsgroup before, so I apologize if this question
has been posted before.

I am thinking of building a miniature backup power system for my living room
using eight 12-volt Sealed Lead Acid (SLA) batteries connected in parallel.
(There will be no series connections.)  During a power outage, I'll use an
inverter to make my AC power from this battery assembly.

I have no need for a rapid charging process, and I have read that a
Float-Charge is safest for SLA batteries.  I have not been able to determine
how much current a single 12-volt SLA battery would draw during a
Float-Charge.  Whatever that current might be, I would need a Float Charger
that can supply 8 times that amount of current during a Float-Charge for
this parallel set of 8 batteries.

I am looking for any an all kinds of advice.  Is my plan workable?  What
Float Charger would you recommend that could Float-Charge eight 12-volt SLA
batteries in parallel?  What SLA batteries would you recommend?

Thank you very much in advance,

Neil
Salem, MA USA

 

Neil - Salem, MA USA wrote:

My recommendation would be: do not put 8 batteries in parallel! It's
asking for trouble. Seen it done, seen the hassles it can cause. Two in
parallel maybe, but preferably not even that. I'm sure everybody in the
NG will agree.....

 


An power engineering company I found on the Internet wrote the following:

"PARALLELING BATTERIES
"You should parallel batteries only to create a battery bank with a higher
capacity. We do not recommend paralleling batteries only for charging
purposes, the weaker batteries can hog all the charging current.

"When you parallel batteries, do so with batteries that are the same
voltage, same AH rating and with the same past history. We recommend using
new (identical) batteries. Don't connect new batteries in parallel with old
batteries. Don't connect 7 AH batteries in parallel with 100 AH batteries.
You should charge each battery separately, let them rest at least 12 hours,
and then connect in parallel to create a battery bank. No two batteries are
the same. Once connected, the weaker batteries will draw down the stronger
batteries and eventually all the batteries in the bank will equalize. Until
then, the weaker batteries will hog all the charging current."

Charles, is your recommendation to *not* put batteries in parallel because
of possible problems with charging the bank, as mentioned in the above
quote?  If so, I could do as the quote suggests: I could charge them
separately and then connect them.

I thank you for your response.

Neil
Salem, MA USA

 

Neil - Salem, MA USA wrote:

The basic problem is that the entire battery bank will only be as good
as the weakest battery. As one starts to 'fade' it will pull all the
others down with it, and you will have to disconnect the entire array to
find the weak one. Take some advice based on many years of living on an
island where there is no grid supply.... just use one large battery, or
a number of lower voltage ones in series. (Especially in the case of SLA
batteries, which don't have the longevity of flooded cells).

 

wrote:

 

Charge multiple batteries separately, and discharge separately. When
one battery reaches a given depth of charge switch to the second
battery with a "make before break" switch.

And don't paint all SLAs with the same brush. some can, and regularly
do, outlast FLA batteries.