Charge in parallel or in series? 1

[tipo1000]

Hi,

I use three 6V lead acid batteries connected in series as a 'power supply'. I take out 6V, 12V and 18V. The lowest battery naturally gets 'empty' first because it is discharging no matter if 6V, 12V or 18V output is used. And the highest battery has of course most power left when the lowest battery is empty. All batteries are of same type.

Should I charge these batteries in series or in parallel?

Thanks,
Tipo

 

[itsmoked]

You should leave them in series and charge them all with separate isolated chargers. Occasionally swap the top and bottom batteries.

Depending on the battery sizes three wall plug type chargers would probably work well. Jack them all into a power strip.


Highly recommended:

http://batterytender.com/motorcycle/battery-tender-junior-6v-at-0-75a.html

I suggest you ask them if they're isolated though I'm about 99.998% sure they are.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

I was going to answer similarly, but given the potentially radically different level of charge in the batteries, charging in series would seem to raise the possibility of overcharging the topmost batteries. This potentially requires limiting the allowable charging current, and therefore, the charging time.

Parallel charging may avoid the overcharging, but would result in sloshing the higher charge level battery's charge into the lower charge level.

The most ideal solution would be to individually charge the batteries, and rotate them to even out the usage.

TTFN
faq731-376

 

[itsmoked]

I don't think you're following me IR. I say leave them in series - but they are all being charged INDEPENDENTLY which totally avoids the problem you so correctly are pointing out.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

Sorry, my bad, glossed over that part...

TTFN
faq731-376

 

[tipo1000]

So what would happen if I charge them all in series (or in parallel)? One of the batteries don't get fully charged, or something else?

/tipo

 

[IRstuff]

Already explained

TTFN
faq731-376

 

[itsmoked]

Series would cause over charging of the less discharged and under charging of the more discharged batteries. You cannot do series charging in your case.


Parallel is not an option either. Hooking up lightly discharged batteries in parallel with heavily discharged batteries will cause over charging RATES. Those lead to failed batteries or batteries exploding in your face. You should not attempt parallel charging because of this.

Either do what I described above or if you're insufferably cheap use a single charger and move it from batter to battery until all three are re-charged.

Keith Cress
kcress -

http://www.flaminsystems.com