Weird bms/lipo battery behavior

How-Tos & Esk8 mechanics Esk8 Mechanics
1

Hi guys!
I noticed some strange behaviour on my new lipo pack and I was hoping that someone could help me with it.

I wired 5x 2s 6500mAh ovionic lipos to 10s bms. Charged them from 36V storage charge to 39V - confirmed that all the cells are the same voltage (3.9V). Few days later I checked the cells again and I found that the first cell on the balance lead was 1.83V. (Overall voltage was also around 36,6). I thought for sure something was draining my battery.
A little bit angry and fustraded I disconnected the vesc, and the antispark, checked everything again and confirmed that the first cell is dead.
After some time, checked again and the cell Voltage was back to 3.9 volts. And overall voltage back to 39Volts. This is my 4th diy lipo pack and I have never seen anything like this.

What the…?
Any advice is appreciated.

In the pic the pack isnt wired, and not the final layout but you can see the pack and the bms if needed.

20200414_195821
20200414_1958213024Ă—4032 3.84 MB

2 Likes
2

So you’re saying that the pack has come back from the dead with no charging or other attention?
Could there be any possible way you weren’t making contact with the terminals when you measured it as faulty?

3

No charging- nothing… just sitting there.
I had the same suspicion… but checked the voltage at least 5 times.

4

When the battery tested bad was it directly after any loading? (running the motor or something like that?)

5

No, no load was applied before testing. Would appear insane to have this kind of voltage sag

6

Yeah, it would indicate a dead cell out of the box.

7

Hmm. Will try to apply a load and make measurements right after.

1 Like
8

Exact same thing happened to me a year ago with a lipo build, left at storage charge around 45v came back one day to see the overall charge at 16v and every cell at 1.3~v. panicked like crazy trying to get them out of the board but once I had disconnected everything they returned to 44v. I think it’s just a thing lipos do.

9

I had something similar happen with a pre-built battery that someone asked me to check out. It ended up being a loose/cold soldered/ rusty balance lead. It was still making some contact, but crusty, so the voltage at at the balance leads was low, like 1.5v. Soldered the offending lead back down properly and it hasn’t been a problem since.
Hope this helps.
Gabe

10

That would make sense! Definitely going to check the solder joints (good thing i used shrink tubes with glue… …not).

11

Checked all the connections resoldered a couple in question and they are just fine- the problem remains.
Also, i noticed the first resistor on the bms has some discoloration which seems could be the problem.

Sooo… Anyone has a 10s (~60A) high discahrge bms that they are willing to sell? :sweat: