24 v sla charging

[jdcburg]

Hello - I am new here and am just starting an ebike build. I will be using 24 volt sla power pack (2 12 v 12 ah in series). I may step up soon to a Li pack, so I am thinking about using a 12 volt 5 amp charger I already have, rather than purchasing a 24 v charger that probably won't be optimal for a Li battery. Can I just switch the jumper(s) to make the batteries parallel/12 volts and hook up the 12 v charger, or should I disconnect them and charge them individually? I did a search of the archives and didn't find the answer to this question, although I may have asked it incorrectly. Thanks - jd

 

[chet]

You can charge two 12V batteries connected in parallel at 12V. You can charge each battery separate. Advantage and disadvantage each way balance out.

 

[fitek]

Just charge them in parallel most of the time. If you feel the need to "balance" them periodically, charge separately every couple weeks.

 

[torker]

I'd charge in parallel as 2.5 amps is just about right for a 12 ah sla battery. 5 amps on a single 12 ah would be fine as long as you disconnect it before it overcharges.

 

[dumbass]

Hello - I am new here and am just starting an ebike build. I will be using 24 volt sla power pack (2 12 v 12 ah in series). I may step up soon to a Li pack, so I am thinking about using a 12 volt 5 amp charger I already have, rather than purchasing a 24 v charger that probably won't be optimal for a Li battery. Can I just switch the jumper(s) to make the batteries parallel/12 volts and hook up the 12 v charger, or should I disconnect them and charge them individually? I did a search of the archives and didn't find the answer to this question, although I may have asked it incorrectly. Thanks - jd

The rule of thumb on SAL batteries is not to exceed 25% of of the batts. AHrating or in your case 3 amps. Of course when charging 2 batteries at the same time they are sharing the 5 amps and only getting 2.5a each. However, the weakest battery the the most juice first until the other one catches up to it. If your lucky the charger will start to auto tapper the amps before you cause a problem.

Please remember you can not run batteries in series and parallel at the same time. That is unless you like a lot of sparks. I run both SAL 24v/18ah and Lipo4 24v/20ah packs on the same bikes. In both cases the pack are made up of 2 12v batteries. I built a parallel connector on the bikes . This way when I plug the 2 12v batts into the bike they are parallel connected. But with the same plug on the batts when I plug into my 12v charger they are in series. Even though I have 18v SLA batts I chose to charge at 2a. I use the same charger to charge my lipo4 packs the same why with the same charger. I have been doing this all summer and have never charged any battery individually but I do check the voltage now and then and it is always within .05v from one batt to the other. This is comparing the SLAs and the lipo4s separately of course. And strangely when charging the lipo4s the charge turns off every time at 14.3v or 3.57v per cell. While the SLAs the charger will turn off at 12.9v. And of course I can raise the charging amps with the lipos but I like slow charging at the 2a setting. And I am still not using a BMS on the lipo batts. They are Thunder Sky 12 sealed packs and the supplier told me they do not have a built in BMS. However, I am not sure that they are correct about this because they charge and discharge perfectly. And I don't think that is normal or I am just really lucky yo have 8 perfect cells.

 

[jdcburg]

Thanks to you all for the good advice. I'm sure I'll be back with more questions as things progress - jd

 

[dogman dan]

A 24v 2 amp sla charger is pretty cheap on ebay, if you shop around and wait for a good price. Should be able to get one for around $30-40 including shipping.