Please review my battery pack so I don't make a 🔥

I have a Chargery charger which will do 12s. Here is a picture of the pins on the charger and the balance cable connection diagram for the 12S battery. Please look at how we are hooking up the 12S cells to the two JST-XH 7pin connectors. Does this look right?

Thanks in advance

bms_design bms_pins

sk8l8r · November 13, 2018, 8:50pm

I used that type of foam, you can always stick some fishpaper on it - someone should make sticky back fish-foam

Scream · November 28, 2018, 9:55am

Hey so I just assembled a 10s3p battery today…

The parallel connections went fine. Wiring the series connections went ok as well.

When I went to plug in the balance wire loom it sparked and the BMS smoked. I did check the voltages on each wire and they were in order (from B0 to B10):

4.38 9.37 14.08 18.77 23.4 28.1 32.8 37.5 42.3 47

Something’s not right though… why is the voltage so high? I’m sure all the individual 30q cells only had voltages of 3.42/3.43 when I measured right at the start. Why would three cells in parallel have a higher voltage?

Andy87 · November 28, 2018, 10:20am

can you upload a picture of your battery and a diagram how you wired everything up? something wrong with the voltages. either you messured wrong, or you wired up something different, like a 12s or so

Scream · November 28, 2018, 10:32am

I’ll get onto the pictures tomorrow. It’s late here. I definitely didn’t wire up a 12s. I have 10 even increments of 4.7ish volts. Can’t work our what’s going on but it does seem unsafe so I just built a nice little house out of bricks for it…

Andy87 · November 28, 2018, 10:36am

your max cell voltage is 4.2V … if you increment with 4.7V than something is wrong or you use different cells not 18650s or lipos…

If you have now 4.7V on every cell than they are overcharged. That´s definitly not good.

taz · November 28, 2018, 10:46am

I don’t think Li-ions can get to 4.7V per cell without exploding. Maybe something is wrong with your voltmeter?

legend27 · November 28, 2018, 10:49am

if the voltage is already at 4.38V in the first parallel group, then it’s either not 18650 cells or the battery is overcharged.

Andy87 · November 28, 2018, 10:53am

I´m not sure if they already explode at 4,7V but it´s definitly not good at all. hope it´s just a wrong messurement.

taz · November 28, 2018, 10:54am

Definitely not good. The brick house he built till he figures it out is a good move.

Scream · November 28, 2018, 6:31pm

Thanks guys… so the battery survived the night in the brick tomb.

I measured total pack voltage again this morning and got 42v. Then I replaced the battery in my multimeter (been meaning to do that for a while!)

Got 34.1v across the pack. Balance loom from b0 to b10 goes: 3.42, 6.86, 10.29, 13.71, 17.13, 20.4, 23.8, 27.3, 30.7, 34.1.

I’m quite relieved. Hardly slept at all last night… checked the pack a couple of times in the night to see if it had combusted/was getting warm.

That doesn’t explain why the bms fried when I plugged it in. This pack will still live in the brick tomb until all mysteries are revealed.

Don’t build batteries when you’re tired!

Andy87 · November 28, 2018, 7:19pm

One thing I didn’t understood. You said you measured 42v over the hole pack, but in the same you wrote when you measured the balance leads the max voltage is 34.1v. Was it just a typo? To help us to help you it is still necessary that we get some pictures and if you have a wiring diagram according to which you wired the battery to the bms.

Scream · November 28, 2018, 7:36pm

I measured 42v - then I changed the batteries in the multimeter and got 34.1v.

34.1v makes sense as it’s consistent with what the inidividual cells measured as before I started.

Monster battery build post coming I promise!

Andy87 · November 28, 2018, 7:39pm

Ok, that sound good now. Got it