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/diy/ - Do It Yourself

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1636920 No.1636920 [Reply] [Original]

battery charging question; I have two 12 volt batteries in bank to make one 24 volt battery. When charging, would a 8 amp charge applied to the 24 volt setup be the same as charging with 4 amps to each 12 individually each with their own pos. and neg. ???? Thanks :)

>> No.1636927

which is faster?? op

>> No.1636931

>>1636920
Charging the 24v bank with 12V @ 8A, no.

What kind of charger are you using? It needs to be >24V to charge them at all. The 12V/4A charger is probably putting out like 14V-15V, so charging two batteries in series would require 28V-30V.

If you had the two batteries in parallel, then your 8A current at the same voltage as before would be correct.

>> No.1636933

>>1636920
>>1636931
The 8A @ 24V is 4 times the power of 4A @ 12V.

>> No.1636935

>>1636931
not the op but just curios wouldn't it be dangerous to connect them in parallel if they had been discharged to different levels and therefore that might result in a huge current potentially destroying one of them?

>> No.1636942

>>1636935
If they were two unprotected lithium ion banks, yes. So like a 3s2p bank I think they would call it. But even them, charging the 3s1p with only 3 cells and no balancing or protection would be dangerous.

I assumed OP was talking about lead acid batteries.

>> No.1636946

>>1636935
>>1636942
Sorry for secondpost, I don’t know about the lead acid. If you have one at 12.0V and another at 13.0V, you could get a whole lot of current flowing from the high one to the low. I haven’t done quite as much research on that, but I don’t think it’s nearly as dangerous as trying to do the same thing with a 3.0V and 4.3V Li-Ion hooked up to eachother. Some anon mentioned once that he measured the current between a couple 18650s that were only a few tenths of a volt apart and the higher one was sending a stupid amount of current to the lower one when using nothing but wire between them.

>> No.1637051

>>1636946
18650s will discharge 10a but should only be charged at up to 2.15a, while car batteries require at least 12.9v to even activate the chemical reaction that is charging and the higher battery here is at 13v. It would just drain down to level with the 12v one, might generate heat in the wire but won't boil a battery.

>> No.1637173

>>1637051
>10a
Nah it was a lot more than that. There is a max rated discharge for each cell, but that is for safety and preservation of the cell. They will do much more if you let them run away. The 1500mAh LG cells I have were rated at 15A IIRC but anon said he measured something like 50A+ when he hooked up two mismatched 18650s.

>> No.1637295

>>1637173
I'm surprised there wasn't a fireball and molten lithium everywhere.