Bafang BBS02 750W shutting down at around half battery.

[caseylain]

Ok so first off, I have a 52v battery attached and I flashed the controller with the open source firmware. It has been working fine for many months but recently started cutting out. My display doesn't read voltage, so I hooked up a watt meter between the battery and motor and then taped it to my handlebars so I could watch it. I had thought perhaps the firmware had become glitchy and the LVC was messed up. Yet on the volt meter I watched it drop to 49v under load, rise up to 53v as speed increased, then it would cut out. Importantly, when it cut out the volt meter stayed on, meaning the battery was not cutting out. Only the controller was.

I would assume if my controller was bad, it wouldn't work at all. Not work flawlessly down to 53ish volts then...get tired and stop working. I'm hesitant to try reflashing the firmware since there is a risk of bricking my bike and I use it to make money, I can't afford any downtime right now. Maybe there is something else I am missing?

 

[docw009]

Got a second battery to try?

 

[amberwolf]

I would guess that the controller firmware has a delay in the LVC routine. It sees the drop in voltage (which may actually be lower than 49v, meter displays don't update very often or very fast). By the time it reacts to the LVC voltage has risen already.

Or if the system has a thermal sensor (in either controller or motor), the delay might be because the system would warm up under load. This is not likely because heat should have built up before this point to cause a cutout, not only just then. But something to verify and eliminate.

You can verifiy it's not thermal by letting the system sit till it's at ambient, but with the battery already at this discharge point, then retest. If the voltage drops and the shutdown occurs, it's not likely to be thermal. If it won't shutdown now then it may well be thermal, and you can try the test ride until it does shutdown, and see if it's happening under or just after higher load times after already warming up.


Even less likely, it may be the battery shutting off for an instant then recovering (most BMS won't do this, but maybe yours does) and turning back on before the system can actually turn off or the display blank out, and then the controller shutting off because it's LVC was reached for long enough to trigger (but delayed, as noted above).

 

[caseylain]

• I set the LVC to 1 volt, and it still does it. Of course if it's bugged it may not matter.
• I'm pretty sure I've already done the let it cool down thing inadvertently. Typically my shift slows down significantly toward the end, so it has had time to cool off by the time I'm trying to go home and it starts shutting down.
• Sadly no I do not have another battery to test it with. The BMS I used was one of those cheap DALY bms's so I don't think it has the ability to turn itself back on.

If I'm remembering right the open source software has a check box for temperature sensor. I may try unchecking that next, just in case the sensor is faulty. Will get back with ya'll tomorrow after work.

 

[amberwolf]

Forgot to ask: did it suddenly start doing this, or has it been building up from some lesser starting point / related behavior?

A sudden fault generaly points to a connection issue or similar hardware failure, usually relatable directly to a specific incident (crash, rain, repair, etc), or a setting change (intentional or not).

Gradual changes may also be connections (usually from water intrusion) but are more commonly caused by battery / cell failures.

 

[caseylain]

afaik it was sudden. My daily battery usage hovers around where the cutoff point is. So somedays I hit others I don't. It does get rained on a lot so I guess that is a possibility.