Balancing a grossly imbalanced 14s14p 18650 battery

[Lateksinen]

I read thru but can't find what motor controller you running ? A link ?

I'm running the original BBSHD controller, haven't done anything to it.

 

[Lateksinen]

The BMS can trip due to a cell voltage being too low or due to current being too high. If the current was too high, I'd expect it to trip right away when you give full throttle. The pack voltage looks OK with no load.

If the BMS is accessible, you can measure the individual cell voltages either on the connector or on the row if resistors that do the balancing. If one cell is significantly lower or higher than the rest, it can cause the kind of behavior you are seeing.

Okay. I have measured voltages once before straight from each of the cell pack poles. I'll check those again from the BMS. The motor was once making a weird clicking sound when pedaling with PAS on. It came from the stator/rotor side of the motor. Like something related to magnets. I tried to open the rotor/stator side but did not realize I should have opened the controller side first and detach the wires. Well I then just put the stator side cover back since I couldn't get it open (wires holding). After that the clicking did not happen anymore and I was able to ride 50 km. Then started the problem I'm having now. I'm just wondering if there could have been something wrong with the stator/rotor that caused the clicking and now causes too much current to draw? The BMS is rated for 30A so I guess it should not cut off under normal load. And now it cuts off some times even when I'm not using full throttle. Or perhaps the clicking was completely unrelated to the problem I'm having now, who knows. But to me it seems that there could be something wrong in the motor since both of the batteries cut off.

 

[fechter]

Well, if a wire inside the motor was rubbing against something and wore through the insulation, you could possibly get an intermittent short. Any kind of rubbing inside the motor is bad.

An easy test is measure ohms from any phase wire to the case of the motor or bike frame. This should read open circuit. If you get low resistance, for sure there is a problem. If it measures open, you might still have a problem, just not a short to case. The wires are especially prone to getting damaged where they pass through the axle.

It might be worth opening the other side of the motor and checking the wires.

I also suggest double checking the cell voltages. A common fail mode on a BMS is for the balancing shunt to get stuck on, slowly draining a cell. After manually balancing, a cell may go low again if the shunt is bad.

 

[999zip999]

The ez way to track your batteries problem is to write down on paper like these to show state of charge.
1. 3.90v
2. 3.88v
3. 2.99v

14. Xxx volt.
It makes it ez on all of us.

 

[Lateksinen]

The ez way to track your batteries problem is to write down on paper like these to show state of charge.
1. 3.90v
2. 3.88v
3. 2.99v

14. Xxx volt.
It makes it ez on all of us.

All the voltages are from 4.0 to 4.1. No visual signs of any failure. I'm having difficulty understanding how both of the batteries could have failed.


The nature of the problem has changed slightly also. Now I can't really most of the time even get the screen on (DCP-14), it only flashes quickly and then nothing. Detaching battery did not seem to help.


Yesterday I disassembled the motor. Controller phase wires and ground showed open circuit. On the rotor/stator side everything seemed fine. I couldn't take the rotor apart from the stator, however. But I guess its quite unlikely there's any trouble. When the phase wires were detached the screen still wouldn't always turn on. When I put the motor pack together I actually got it run under no load. Then I took it for a test ride. This time the motor behaved strangly. When I applied throttle it would not accelerate smoothly, instead the motor had kind of like short breaks of no power. I mean the power was not continuous. I haven't encountered it before. Then after this happened I couldn't get the screen on anymore and quit.

Either I messed something when putting the motor and controller back together (however it ran smoothly when testing under no load) or the problem somehow progressed with no relation to the disassembly. Does it seem like a controller related problem if the power is not smooth but discontinuous when applying throttle (gently). Should I do some more measurements from the controller? Btw, thanks for your contribution. I appreciate it.



EDIT: I went to test the motor again after letting it rest overnight. This time the display turned on and showed Error 04H Controller report. I understood this could be related to throttle being faulty. I then put the bike on PAS mode and rotated the cranks and the motor started spinning with no problem. This lasted for like 5s until the bike shutoff again. Then I couldn't get it on after that. Tried to disconnect the throttle cable if that would help but it didn't.

I then connected the programming cable to the bike to see if I could get it run without display. Again, rotating the cranks would get the motor spinning but hitting throttle did nothing.

Now again, display is not turning on, just flashing. So to sum up - Error 04H showed, throttle is not working but PAS is when I manage to get the display on (which appears to happen only after letting it rest for long enough). Detaching throttle does not help. Something inside the controller related to the throttle but not PAS is messing up now? Or display faulty? Or perhaps the throttle just died accidentally on top of the mysterious, previous problems. Aaargggh.

 

[Lateksinen]

Some new testing. The error 04 was my bad, I mixed the throttle and e-brake cables accidentally.


Sometimes the Display only flashes, sometimes it turns on and I'm even able to drive a couple hundred meters after it suddenly turns off.


I checked the phase wire resistances, they were all as they should be. So it doesn't seem like a controller problem.


Cell pack voltages are all equal 4.12v now (not completely charged). After the power cuts, volt meter reads 7 volts from the cables coming from the battery. So in my opinion it must be the BMS cutting off. I just can't understand why. I'll check the wiring harness again as both of the batteries do the same. Either there's something wrong in the bike or both of the batteries have faulty BMS or cells (cells seem ok based on voltages). Load testing the battery with a 50W 230v Light bulb was fine.

 

[fechter]

It's hard to say, but I'd guess there is a short spike in the current that is tripping the BMS over current protection. Most of these BMS circuits respond very quickly to over current. One test would be to bypass the BMS long enough for a test. A wire from the battery negative to the pack negative on the BMS will keep it from turning off.

I had a similar issue with one I was using. I ended up adding some resistors to the BMS shunt to increase the current trip point and it's been good since.

 

[Lateksinen]

It's hard to say, but I'd guess there is a short spike in the current that is tripping the BMS over current protection. Most of these BMS circuits respond very quickly to over current. One test would be to bypass the BMS long enough for a test. A wire from the battery negative to the pack negative on the BMS will keep it from turning off.

I had a similar issue with one I was using. I ended up adding some resistors to the BMS shunt to increase the current trip point and it's been good since.

Sounds legit. Today when I plugged the battery it made a sound of electric spark. It also made the same sound before the bike turned off once. Could it be that the controller intermittently creates a shortcut which creates high current = spark and BMS shutdown? Also the first time this whole turning off started to happen the screen showed error 30H. Now it displayed again. I understood it is a communication error and can be related to the controller. I also noted that the controller got pretty warm after just a quick test run.

It think it would make sense it the problem was somehow related to controller as both of the batteries behave in the same way.

 

[fechter]

The spark when connecting is normal. This happens when the battery is trying to charge the main capacitors inside the controller.

Controller getting warm after a short run could be due to excessive current, which could be tripping your BMS. This could be something in the motor or controller. Sounds almost like one of the windings in the motor is shorted. Maybe not to the shell, but sometimes windings can short against each other and be hard to detect.

One simple test is to lift the wheel and spin the motor by hand and see how much resistance there is. A shorted winding will create quite a bit of drag.