Charging gel cells in series

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Gel cells should all be charged in parallel from a constant voltage source. Usually about 13.8 to 14,0 volts. You might install a fuse in each leg of the summing point just to be safe.

On Friday, June 26, 2015 at 12:08:38 PM UTC-4, snipped-for-privacy@gmail.com wrote :

me. He uses these in his fire alarm panels and wants to keep a quantity in stock for when one of these panels goes down for battery failure. I've exp lained to him about the need for trickle charging these while they're sitti ng on the shelf, and rather than sell him 12 individual trickle chargers I was wondering if anyone knows of a cost effective series charger whereby I could put perhaps 6 in series and charge them all at the same time. I would probably not want to go above 6 and I would not do this with anything othe r than new batteries all of the same type and rating. Thanks, Lenny

I was under the impression that parallel charging was not the way to go bec ause it is difficult if not virtually impossible to equalize the current th rough each battery. Batteries having a lower terminal voltage would draw mo re current. The inverse would then be true with a higher terminal voltage. In series the entire string gets the same amount of current. Lenny

Since the cells in each battery are in series, it seems logical, to me at least, that charging a bunch of batteries in series is appropriate. Or am I missing something?

from me. He uses these in his fire alarm panels and wants to keep a quantity in stock for when one of these panels goes down for battery failure. I've explained to him about the need for trickle charging these while they're sitting on the shelf, and rather than sell him 12 individual trickle chargers I was wondering if anyone knows of a cost effective series charger whereby I could put perhaps 6 in series and charge them all at the same time. I would probably not want to go above 6 and I would not do this with anything other than new batteries all of the same type and rating. Thanks, Lenny

go because it is difficult if not virtually impossible to equalize the current through each battery. Batteries having a lower terminal voltage would draw more current. The inverse would then be true with a higher terminal voltage. In series the entire string gets the same amount of current. Lenny

Well, isn't a 12V rechargeable battery, itself, a _series-connected_ set of cells -- from 6 to 8 of'em depending on the chemical technology?

The OP did say " ...new batteries all of the same type and rating ..."

Jonesy

Lead (and lithium) based batteries are charged to a specific voltage, and are therefore well suited for parallel operation.

During standby charge, you want to control the voltage, not the current. In fact, even if the batteries are not closely matched, you can perfectly well keep them on standby charge in parallel. The battery that has more self-discharge will then automatically draw more current.

You can run batteries in series, but they must then be closely matched. A battery is simply a set of closely matched cells connected in series.

In your situation, just hook several batteries in parallel and use one charger to keep them all fully charged.

To be completely safe, you might want to fully charge them individually before you connect them together. If you connect two batteries with considerably differing charge state, one battery will charge the other at an uncontrolled current.

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RoRo

And if the batteries are charged in parallel it makes no difference if one is removed. But if charged in series once the customer needs another battery the customer must remove ALL the batteries in that series string from the charger. Eric

** The cells in a particular battery have a great deal in common - eg same origin, age, capacity, number and level of charges and discharges.

Various 12 batteries likely have none of the above in common so charging in series will not suit more a than one of them.

In the OP's case, with all new and unused batteries of the same type, parallel charging with a fixed maximum voltage of 13.8 is the most practical method as one can use a standard charger.

Each battery will initially draw the current it needs until all are fully charged, then the current will taper off to a trickle in each.

Gel and SLA cells behave very differently to NiCd and NiMh cells.

.... Phil

On Friday, June 26, 2015 at 12:08:38 PM UTC-4, snipped-for-privacy@gmail.com wrote :

me. He uses these in his fire alarm panels and wants to keep a quantity in stock for when one of these panels goes down for battery failure. I've exp lained to him about the need for trickle charging these while they're sitti ng on the shelf, and rather than sell him 12 individual trickle chargers I was wondering if anyone knows of a cost effective series charger whereby I could put perhaps 6 in series and charge them all at the same time. I would probably not want to go above 6 and I would not do this with anything othe r than new batteries all of the same type and rating. Thanks, Lenny

I can imagine haw this might be a concern in high current charging, but how important in float or trickle applications is it that all batteries be fed with the same series resistance, such as equal length leads from the charg ing source? Lenny

Phil Allison wrote in news: snipped-for-privacy@googlegroups.com:

*EXACTLY* The charger should be rated for the maximum total AH capacity to be connected to it and needs to be set for SLA batterys and to have a constant float mode.

A 12V 10W bulb in series with each battery will prevent excessive current flow allowing discharged batteries to be recharged safely and also provides visual indication of any shorts.

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Ian Malcolm.   London, ENGLAND.  (NEWSGROUP REPLY PREFERRED)  
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** Most Gel/SLA chargers have affixed maximum voltage between 13.8 and 14 volts which IS the float mode. A fully charged 6 cell battery will draw only a trickle of current at this voltage.

They also normally have a "current limit" feature that operates when a partly or fully discharged battery is connected, which ought not apply in the OP's case.

** With bulbs like that fitted, a SLA charger rated at say 3 or 4 amps would do fine with 6 x 7AH batteries at once in the OP's situation.

.... Phil

What happens when he uses one out of that string? The next battery will need more charging current. What happens when he has less than six batteries in stock? Why complicate things?

What happens when he uses one out of that string? The next battery will need more charging current. What happens when he has less than six batteries in stock? Why complicate things?

As I recall in a past lifetime, Vesta had a display rack that held a collection of 2 - 6 or 12volt batteries. It came with a fixed current trickle charger for all the batteries to be connected in series. It would seem to me the matter is being made into a mountain rather than a hillock, the answer would seem to me to be a matter of education since both methods would work in the right hands.

** Sure, it's possible to make the 6 x 12V Gel batteries in series idea work. But you would have to design and build a one off charger rather than use a cheap, off the shelf unit and a few bulbs.

Plus outputting over 84V DC is getting a bit hazardous too.

... Phil

Lead-acid batteries charging is VOLTAGE-controlled, unlike NiXX. So parallel charging - well, floating actually - is what is required. Refer to the cell manufacturer for the appropriate voltage and do as Tom Miller suggested.

Charge 'em in parallel, except put an incandescent light in series with each so the current can't be hogged by one. Some "smart" chargers might object to that, but a dumb float charger should work just fine.

I'd suggest that, if your need is so infrequent such that you need to recharge 'em, you're stocking too many replacements.

Find a high-turnover supplier with short delivery time and stock fewer batteries. Fresher is better.