Problem with my ebike battery

Yogesh

1 mW
Joined
May 15, 2022
Messages
12
I made a ebike a year ago and i changed hub motor because i broke aluminum disk in previous one and changed 3 controllers. I used a 36v battery max voltage 42v after 2 months i become greedy and added another 1s in 10s battery with other bms now i was using two batteries with 2 bms with 2 different chargers 1 battery was a 42v battery other was 4.2 v so in total i get 46.2-46.5 v .Now the problem is when my ebike was 3 months old my battery autocut itself at near 36-37v after 3 months it started autocut at 33v
But now it even touched 31v .what's the matter with my ebike battery bms??? Rest of the function are normal.
 
What voltage are each of the cell groups when the battery cuts off?

Most likely you have cell groups becoming more and more unbalanced over time, so it drops in voltage more and more.



Yogesh said:
I made a ebike a year ago and i changed hub motor because i broke aluminum disk in previous one and changed 3 controllers. I used a 36v battery max voltage 42v after 2 months i become greedy and added another 1s in 10s battery with other bms now i was using two batteries with 2 bms with 2 different chargers 1 battery was a 42v battery other was 4.2 v so in total i get 46.2-46.5 v .Now the problem is when my ebike was 3 months old my battery autocut itself at near 36-37v after 3 months it started autocut at 33v
But now it even touched 31v .what's the matter with my ebike battery bms??? Rest of the function are normal.
 
amberwolf said:
What voltage are each of the cell groups when the battery cuts off?

Most likely you have cell groups becoming more and more unbalanced over time, so it drops in voltage more and more.


But why doesn't bms balance it. I will tell you each cell potential difference after some time.
 
Assuming it is an imbalance (that's what we need the group voltages at empty cutoff to find out), then if it's a balancing bms (not all are) it might not have enough shunting ability (50mA or less is typical) to keep up during a normal charge cycle. It might need at least overnight each time to keep up if the cells are not all equal capability/capacity; the worse they are the harder it is for the BMS to keep up.

Using less of the pack's capacity, and not pushing it as hard (not as many amps) can help with this, by not unbalancing them as much to start with.

If it's not a balancing BMS, then you'd have to manually balance them every time it's needed (which will be more often the more different the cells are from each other in capability, and the harder the pack is pushed and the more of it's capacity is used each time).

(or replace it with a balancing BMS, or install balancing boards, or replace the cells with well-matched good quality cells capable of handling the load and with more capacity than you need, etc).

The solution will depend on the problem. :)
 
Back
Top