48v 20A battery issue

[just1]

Hi!
I just finished my first DIY electric bike project and get crucial problem with battery.First time when I went to test ride everything works fine - speed was about 30-35 km/h But when battery reached ~65% level - whole system shut down.No error messages.Just shut down.After that I turn it on but it shut down every time when I pull throttle a little bit faster than ~ 10km/h.

My set-up is:
Bafang 500w 48V wheel
controller 20A
and DIY battery 48V with 20A BMS
Battery is made of 18650 cells with 13s4p sheme ( 52 cells are Panasonic NCR18650B 3400mAh with pcb protection )

I charge battery again but next time when battery goes to 75% level it shut down again...Now it shut down even when charged to 95%!!
What I did wrong? Did I kill my battery?

[tarekmid]

Hey, I'm not an e-bike super expert yet. But I think your BMS that is in your battery keeps cutting your battery. Maybe the BMS is designed for a different voltage like 52 Volts?
I'm just guessing

[commuter ebikes]

Hi!
I just finished my first DIY electric bike project and get crucial problem with battery.First time when I went to test ride everything works fine - speed was about 30-35 km/h But when battery reached ~65% level - whole system shut down.No error messages.Just shut down.After that I turn it on but it shut down every time when I pull throttle a little bit faster than ~ 10km/h.

My set-up is:
Bafang 500w 48V wheel
controller 20A
and DIY battery 48V with 20A BMS
Battery is made of 18650 cells with 13s4p sheme ( 52 cells are Panasonic NCR18650B 3400mAh with pcb protection )

I charge battery again but next time when battery goes to 75% level it shut down again...Now it shut down even when charged to 95%!!
What I did wrong? Did I kill my battery?

So this is a 13.6 Ah battery, right?

I can appreciate how frustrating this is when your new battery shuts down at 95% charge.

My 19.8 Ah battery (with a 100A BMS) operates correctly and cuts out if I try to draw high current at 50% discharge. At this point, I can either ride at greatly reduced power levels or recharge the battery. A 20A BMS will allow a lower current draw.

Try the following experiment. See what this battery will allow you to do. If the circuit breaker in the BMS trips, unplug and plug in the battery (waiting 10 seconds while it is unplugged). Ride at a reduced power level. If it trips again, unplug and plug in again and further reduce the current draw. Performing this experiment, what is the maximum amount of current that your system will allow you to draw?

On a separate but related note, I once owned a battery that would fail to deliver adequate levels of current. It was very frustrating! I remembered that I had dropped the battery on a concrete floor. Upon inspection, it was discovered that I had disconnected one of the rows when I dropped the battery. It worked fine after I repaired the broken connection.

[just1]

Thanks for answers!
My battery is 12.80 Ah.I already get that 13s4p setup is too low to output stable 20A , so I purchase another bunch of cells to upgrade battery to 13s 5p. Therefore it is expected that BMS shut down the whole system when I lower than 65% power. But now it shut down even in 95% power!! I stopped and tried to plug/unplug battery ( it worked previously ) but now it just didn't start at all. So is it possible that I killed my battery? I take about 3-4 rides total.

[commuter ebikes]

I wonder if you don’t have a loose connection somewhere in the battery.

Are you saying that the battery behaves differently now than it did 3-4 rides ago?

The BMS should have protected any cells from going out of balance.

Since you are going to rebuild the pack, you might consider using at least a 50A BMS.

[MoneyPit]

So you have a 20a controller and a 20a BMS... Are those both peak numbers? What about the continuous number for each? Or vice versa. Usually when people talk about controllers they use the peak number.

Are you sure your battery's continuous number is at least equal to the controller's continuous number? Are you sure that your battery's peak BMS number is at least equal to the controller's peak number?

Next,
I have a bike where my (single) battery's continuous BMS matches the total of my two motors' controller peak number. I have a 35a peak front Bafang hub controller and a 30a peak BBSHD (really that is peak and continuous I guess) and those two together are 65a. My battery has a custom 65a continuous, 90a peak rating.

If I am drawing the battery down to lower volts, and I am going up a hill AND I take both throttles wide open I can trip the BMS. Its getting a peak from the controllers that lasts longer than the BMS can hold its own peak number.

For this reason, next time I do a battery I'll make sure continuous BMS value exceeds continuous controller output by at least 5-10 amps. Since you could also be matching... you could have the identical problem.

[commuter ebikes]

That battery sounds like it can really put out the juice.

[MoneyPit]

It does indeed. 20ah brick using 25r cells. I prefer the 25R for its ability to take a beating. More than willing to put up with the lesser capacity in exchange for the ability to flog it, plus the lower heat and reasonable cost.

[JPLabs]

I'm surprised nobody asked if your pack is reaching proper voltages, first. Also, pack voltage after the ride, when it's shutting down.

Does pack voltage drop way faster than it should?

One parallel cell group with low voltage could cause this kind of behavior. As fast as it progressed, though, it almost sounds like one group will discharge, but not recharge. I don't know if that's possible? A bad cell can lead to this kind of thing, over many cycles as their mates wear out from working too hard, but not so fast as 4-5 charge cycles, as far as I understand. So, hopefully all your cells are fine.

I'd check connections in the pack, and voltages of each group. Actually, check voltages first. If you don't have a low group, then look for overall wiring issues. If you find a low group, you know to look there first. Maybe that will tell you something.