Battery balancing

[yooper2001]

I bought a new aliexpress silverfish battery, and of course when it got here, it had no voltage. Well, they said return it for refund, but you can't because of cost, and customs paperwork, so I offered to troubleshoot and take pics for them. I found right off the bat that the wire to the bottom output ports was desoldered/broken. I then tried to measure the output from the output post, and it was 4.15v. They said it was a bad BMS....and they can send me a new one.

Well I also went to measure the battery groups just in case this BMS blew a cell....and found then 3 groups of 3.92...and 3 groups of 3.80v......this is also a imbalance, so even if I got a new BMS it wouldn't work?

Is there any way I can balance them enuff to charge with a new bms without breaking the welds? because I don't have a spot welder.

Thanks

 

[E-HP]

Well I also went to measure the battery groups just in case this BMS blew a cell....and found then 3 groups of 3.92...and 3 groups of 3.80v......this is also a imbalance, so even if I got a new BMS it wouldn't work?

Is there any way I can balance them enuff to charge with a new bms without breaking the welds?

You should ask the seller if the BMS for the pack has a balancing function. Cheap ones don't and only protect the pack from low or high voltage (and/or overcurrent). Not a good sign that it started off with an imbalance.

Anyway, yes, you can charge up the individual groups one at a time, at the same contact point that you took your measurements. Search on Amazon, or wherever, for a 1S lithium or lipo battery charger. The run around $5 to $10, depending on whether it's powered by a wall wart or just any USB adapter.

 

[docw009]

The dumb (no bluetooth) BMS units found in most ebike batteries will work with cell groups at 3,80 and 3.92 volt, I've seen them work with a ,70 volt difference. That will not shut off the battery. What trips the BMS is if a cell group falls under 3 volts, Check all the series groups, ten for 36V and thirteen for 48V for low voltage,

Still, if you have cells at 3.9V and cells under 3V, that's an unsafe battery in my opinion, I'd collect some pictures or phone videos of your measurement process, a summary of the voltages and file an aliexpress dispute. I've found aliexprress pretty reasonable.

 

[yooper2001]

The voltages are good...*except unbalanced by .1v* but the bms only puts out 4v. (Battery direct wire 50v) so they said they would send me a bms... I'm gonna ask for a shrink sleeve too..

I got it for 80 bucks with all the coupons on aliexpress early November sale.. it was supposed to be 21ah and 6 parallel...but it's only 5p so....maybe 17ah...but 17ah is better than dead battery...and 80 bucks.. I will just mention it in the review

 

[docw009]

It's amazing they can ship a silverfish for 80 bucks, Well, if the voltages are good, gotta be a bad BMS.

Silverfish has a keyswitch, but that switches the power directly. The BMS is always powered on, so maybe a cheap one burned out.

 

[yooper2001]

Ok, I now feel like an idiot after opening the pack up. First of all, even if this battery was configured correctly, it has only 1800mah cells, so the '21ah' battery could only theoretically be a 9ah battery.
Now I cannot wrap my head around what this configuration actually is...so if one of you builders could explain it to me... my brain can't compute what configuration this is besides a bomb...can you guys help me out?
I had measured where they had the bms lines to get the earlier group voltages (not thinking)

At least I have a silverfish case a very expensive one.

 

[E-HP]

Ok, I now feel like an idiot after opening the pack up. First of all, even if this battery was configured correctly, it has only 1800mah cells, so the '21ah' battery could only theoretically be a 9ah battery.
Now I cannot wrap my head around what this configuration actually is...so if one of you builders could explain it to me... my brain can't compute what configuration this is besides a bomb...can you guys help me out?
I had measured where they had the bms lines to get the earlier group voltages (not thinking)

At least I have a silverfish case a very expensive one.

The cells are configured as 13S5P.

 

[yooper2001]

Good...so just a 9ah instead of a 21ah...thank you

 

[docw009]

Yes, 5P x 1800mah is 9AH, but what can you expect for 80 bucks. Yes, it looks like a bomb. No cell holders. BMS wires laying on the nickel.

Better built packs use a plastic cell matrix and lay the BMS wires on the side of the cells.