Help with lead acid battery charger!

[mastershake916]

Hi, I'm going to be running 3 12v 18ah AGM batteries and I need buy a charger. It's my understanding that it's better for the batteries to be charged individually, its this so and how much of a difference is there?
I was looking at getting 3 of these chargers, which at 4 amps should charge it in a reasonable amount of time.
Energizer 84028 12V 4A Battery Charger and Maintainer
http://www.newegg.com/product/product.aspx?Item=N82E16882691035

Thanks.

 

[dogman dan]

4 amps is a bit fast for charging smaller sla's. Usually a 2 amp charger is considered the max for a 12 ah one. Do they make that charger in a 3 amp mabye?

Fast charging is not one of the things you get with lead. But I understand getting started with lithium is expensive.

 

[EVan]

I wouldn't use a battery intended for automotive (flooded) battery charging with a small AGM.

The smallest Soneil might be good: http://soneil.com/12_volt.html

Bear in mind that charging the batteries seperately may help keep them balanced, but you have the risk of one charger failing, and then driving off without noticing. That can destroy the uncharged battery!

 

[dogman dan]

Another thing to consider, if you are treating the slas nice, like only 75% depth of discharge, moderate amps, etc, they won't get so badly out of balance.

I'd buy two chargers, one a 2 amp 36v charger and string charge most of the time with that. Using a voltmeter, occasionally check voltage both at full charge and after a ride, and balance charge only if needed. The balancing charger could be an even lower amp one, to really slow charge when balancing.

 

[amberwolf]

FWIW, it is likely that those 18Ah SLAs have a max charging rate of 5A, if they are like mine.

Any charger that holds a constant voltage output for the final voltage they're to be charged to, with a current limit to prevent any current flow over whatever their max rate is, will work. Even a lab bench power supply (which is how I used to charge mine).

If you were charging in 24V increments, 24V or 48V, I would say try to find a used Pride or other brand powerchair / wheelchair charger, as often those go up to 4A max, and have an end-of-charge light as well as a float charge to maintain the batteries so they can be left plugged in all the time when not being ridden.

I'm not aware of a 36V version, though, just a 24V. With 24V versions, charging 48V is as simple as hooking one charger across each pair of SLAs, since the chargers are isolated (at least, the Pride chargers are. Pride chargers are also potted, so they're weatherproof, small, and vibration-resistant to be left bolted to the powerchair/wheelchair during use).

 

[dumbass]

The max recommended charge rate for SLA (lead) batteries is 25% of the rated AH. I have 6 18ah SLA batteries that I charge at one time with one Black & Decker 2,6,10a charger. Depending on how many batteries I am charging determines how how I set it. But I prefer to normally use the 2a setting. Keep in mind that the amperage is devided by the amount of batteries being charged. Therefore, at 10a charging 3 batteries each battery will only get 3.3a. And your 18ah barrteis can handle 4.5a. Because the charger will tapper the amperage as the batteries gain voltage using the 10a setting is not harmful. And yes I have done it. Actually i have used this same charger to charge my Lifepo4 packs the same exact way. In fact i have actually charged both SLA and lifepo4 batteries together at the same time. And yes it does work fine.