Dumb question(s) - charging lead acid batteries

[Marks256]

I have found myself with some free time lately, so i figured now would be a good time to learn about batteries...

I have an automatic 12v lead acid battery charger (it came off of one of those carts you see old folks riding around in in Walmart) It says it can charge Lead Acid batteries at 6A.

I also have 2 small lead acid batteries (12 volts a piece, 4.5A/hours for 20 hours). Can i use that 6A battery charger to charge them? Will the "auto charge/maintain" function on the charger work? Or will the charger force too much current through the batteries and damage them? What about charging them in parallel? Or is that just plain stupid?

Also, the charger has 3 wires coming out of it? They are Red, Yellow, and Black... What do they do? I know that Yellow is + and black is ground, but what is the red? I will take some pictures if that will help... Actually i know it would be a good idea... I will post this then run down to the basement and take a picture quick...

Thanks.

 

[Marks256]

Ok. Here is a picture of the charger and of the 2 batteries. The charger charges at 12.6v

Also, the little tag on the yellow wire says something to the effect of "+12 Relay Only", so i am assuming the red wire is the charging wire? what would be the purpose of the relay? turn charging on and off? Switch batteries? (the people cart the charger came from had 2 12 volt batteries in a series for the 24 volt motor, so maybe the relay chose what battery to charge?)

 

[HarveyH42]

A few months ago, I was asked to get a 36 volt golf cart charger working. Kind of an oldie, but found the owner's manual online, and included the schematic. The relay switched on the charger when plugged into the cart. The batteries needed some charge to start, wouldn't do complete dead batteries. Yours is likely to be similar. Search for your charger, manufacturer usually has owner's manuals online.
I probably have the files still on my computer, but not likely to be a huge help, very simple design.

 

[Marks256]

Ok. I will give it a go here in a few minutes. I didn't bother looking for a data sheet because it seemed like a generic charger, but i will try.

What about for charging my 4.5A/H batteries?

 

[HarveyH42]

Not really knowing much about battery charging. The rule seems to be 1/10th current capacity. So 450 mA max, and around 14 volts. There are several threads dealing with SLA charging circuits.

Here's a link to my post about the golf cart charger, pictures of the schematic...

https://www.electro-tech-online.com/threads/lestronic-ii-7850.33861/

 

[chemelec]

Ok. Here is a picture of the charger and of the 2 batteries. The charger charges at 12.6v

Also, the little tag on the yellow wire says something to the effect of "+12 Relay Only", so i am assuming the red wire is the charging wire? what would be the purpose of the relay? turn charging on and off? Switch batteries? (the people cart the charger came from had 2 12 volt batteries in a series for the 24 volt motor, so maybe the relay chose what battery to charge?)

Those batterys appear to be a 4.5 A/H Rating, Base on a 20 Hour Discharge rate.
(About 0.225 Amps continuous output for 20 hours.)

NOT 4.5 Amps for 20 Hours.

The Charging current should be about 450 mA, maybe a bit higher to start, than tapering off.

But 6 Amps is way to high.

 

[killivolt]

? Where is the DC side of this Schematic ?

Here's a link to my post about the golf cart charger, pictures of the schematic...

https://www.electro-tech-online.com/threads/lestronic-ii-7850.33861/

In the schematic are those shot key diodes in the secondary and is that a half wave rectifier or does it feed back to once reaching full charge ?

 

[HarveyH42]

Didn't really have to get into it that much. The contacts on the relay were bad on one, so I just put a jumper on it. The other on had a bad capacitor, found on that was pretty close, seemed to work. Got 39 volts output. Just got lucky on both chargers.

Almost forgot, there was a circuit board for controlling the charge, don't remember if it shown in the diagram.

The board is a timer from the schematic...

 

[tab a]

I wonder about this. "Standard" charging for SLAs does follow the rules as noted. Rapid charging--which you'd probably want in the cart this came from, seems different, and I can't find a lot of info on exactly what the parameters are.

You can find chips used for SLA chargers that control current up to 5CA, and chargers that will recharge a SLA in about an hour.

If in fact this voltage is being controlled at 12.6 (very low), maybe this charger would work--and be very fast?

 

[chemelec]

I wonder about this. "Standard" charging for SLAs does follow the rules as noted. Rapid charging--which you'd probably want in the cart this came from, seems different, and I can't find a lot of info on exactly what the parameters are.

You can find chips used for SLA chargers that control current up to 5CA, and chargers that will recharge a SLA in about an hour.

If in fact this voltage is being controlled at 12.6 (very low), maybe this charger would work--and be very fast?

There are a Few SLA Batterys that are designed for a
Greater starting current. I have seen a few at 3C. But its only the Inital start current.

And I Extremely doubt any SLA battery or any lead acid battery can be Fully charged in one Hour, or even in 3 hours.

 

[tab a]

I agree with pretty much all you've said, but the fact is there are manufacturers who are selling SLA "rapid" chargers. Some (all--how else would you accomplish it?) are using, at first, full current capacity--6 to 10A. See

https://www.powerstream.com/SLA.htm

Is it as good on the battery as slower methods? I agree, probably not. But that wasn't the OP's question.

If anyone's aware of 'good' literature on charging SLA's with high current I'd like to see it 'cause I haven't been able to find it. Everything I've seen goes into detail only on the slower methods.

If it was mine I'd be inclined to put the charger on a partially discharged battery--maybe a car battery--and measure V and I every 30 minutes or so for several hours. I'd think this would give you an idea how 'smart' it is, then you could decide how important maximizing battery life, vs charging time, is to you.

 

[chemelec]

I agree with pretty much all you've said, but the fact is there are manufacturers who are selling SLA "rapid" chargers. Some (all--how else would you accomplish it?) are using, at first, full current capacity--6 to 10A. See

https://www.powerstream.com/SLA.htm

Is it as good on the battery as slower methods? I agree, probably not. But that wasn't the OP's question.

If anyone's aware of 'good' literature on charging SLA's with high current I'd like to see it 'cause I haven't been able to find it. Everything I've seen goes into detail only on the slower methods.

If it was mine I'd be inclined to put the charger on a partially discharged battery--maybe a car battery--and measure V and I every 30 minutes or so for several hours. I'd think this would give you an idea how 'smart' it is, then you could decide how important maximizing battery life, vs charging time, is to you.

As it says in that article, Fast charging is only recommended for Flooded type cells, Where the water can be replaced. SLA Batterys are Not suitable for this type of charge.

But anyone can sell anything. That doesn't mean its a good system. And it probably Greatly reduces Battery life.

 

[wingerr]

I wouldn't use that charger if you want to maintain those small batteries in good shape; Walmart has a Schumacher charger for under $19 that charges at two rates, 2A at 14.5V initially until the charge rate tapers off under 500mA, and then switches to float charge at 13.2V, which can be left on indefinitely for maintenance.
Works really well for motorcycle batteries and the like-

 

[tab a]

<As it says in that article, Fast charging is only recommended for Flooded type cells>

I don't see that under the SLA charging section. Is it somewhere else?

<And it probably Greatly reduces Battery life.>

That's really the question isn't it? Panasonic, in their SLA Technical Handbook, lists rapid charging as an option. They say little about it and give almost no details. I would suspect that if it is 'death' to batteries they would condemn it.

I'd still like to see some kind of study--using high charge current, appropriately monitored--that compares battery life with this method vs slower methods. Getting, for instance, 10% fewer cycles from your battery, would be very different than destroying it in say, 10 cycles.