crotch_rocket

Hi folks,

I'm building a custom electric bicycle, and I'm using SLA batteries, 3 12V17AH wired in series for a total of 36V-17AH. I have two chargers at home, a 12V 1-2AH and a 48V 20AH smart charger. Both are smart chargers. I was wondering, is it a bad or ok idea to charge the pack with the 48V 20AH charger? And if not, can I modify the charger to do this? It's single rated, so I don't think it'll adjust. And if not, can I use the 12V 1-2AH charger and wire the batteries as a series for the motor, and leave on a wiring configuration in parallel for the charging setup?

morph999 

Very bad idea.

Yes, you can wire it up in series so that you can disconnect into 12v blocks. I had the same thing with my SLA's. I do the same thing with my Thundersky LIfepo4 too. Use anderson powerpole connectors to do it.

chvid

Roger that. Very bad idea.

crotch_rocket

Sooo then, how about the idea of leaving a parallel wired setup for strictly recharging with the 12V 1-2Amp charger? Or would that cause problems and electrical issues with the battery pack?

morph999 

How are batteries hooked up to each other now? If you can get to the actual terminals without removing the wires, you can charge them individually as they are but most of the time, this is not possible with SLA's because of how they are hooked up.

There's a way using anderson connectors where you can plug them all in a series for the 36v17AH setup that you have now and then unplug them all and charge them individually. That's what I would do. I do that now with my lifepo4. As far as doing them in parallel, you'd have to ask someone else because I've never done that but I've heard that it can be done. My question in doing that is what if one battery is a little less than another, would it still be charged fully if done in parallel? I'd charge them individually by disconnecting anderson connectors (very convenient). The connectors that I have on my SLA just slide right off so I could charge them individually very easily.

dumbass 

Yeah, I've done series connections for riding and parallel wired for charging. i used a simple setup of Anderson connectors. All I had to do is make 1 simple plug change when riding I pluge the pack into plug 1 and when charging I pluged the pack into plug 2. A real no brained.

As for the batteries having different levels of charge this is not a problem with SLA (lead) batteries. You can charge a totally dead battery with a fully charged battery if you want and both batteries will be fine.

Bob

crotch_rocket

Cool, thanks for the info.

I Can't wait to see what I can put this beast through!

crotch_rocket

OK, so I went ahead and bought an extra battery for a full total of 48 Volts, and 17AH. I figured, OK, since it's the right voltage, I guess it would be worth it to try out this Chinese made 48V 20Amp charger.
The next day, my whole house smelled like hydrogen sulfide fumes, the batteries were boiling hot, and the plastic even melted onto each other!!!

Any suggestions on a better charging setup? I ditched the 48 volter. I have a 12Volt, 2Amp smart charger, can I wire up the whole thing in a parallel setup for charging, or do I have to do it in 12Volt blocks? The setup right now is in series (12V/17Ah) for the motor and controller.

Sangesf

Why would you think that 20amps into a 17ah set of batteries would be a good idea?
Wish I had seen this thread earlier..

dougmc

Charging at a 1.2C rate. Most LiPos are meant to be charged at rates up to about 1C (so I'd expect 1.2C to not cause any real problems) but this was a SLA battery and they're usually meant to be charged at a lower rate -- C/10 or so. (So 1.7 amps, though 2 amps would be fine too.)

Also, just because the nominal voltages match, that doesn't mean that the cutoff voltage of the charger is exactly correct.

crotch_rocket is quite lucky that the only thing that happened was that the house got stunk up!