Bafang BBS01 250W dead (or battery)?

[Spesseh]

Hi,

Biked a steep hill with heavy baggage in carrier. Suddenly the drive died and it won't turn on.

I changed the controller without helping. Measuring the battery at its terminals shows 41V. Measuring the volt between battery and drive is initially 0 once I power on the battery. Then increases slowly. When I hit the power on button for the drive the voltage drains slowly.

See video that shows this behavior (watch the multimeter):
https://www.dropbox.com/s/e0q30hmymenoz19/2017-09-08%2022.05.10.mp4?dl=0

Any idea what is going on? Burnt the drive or killed some battery cells? Suggestions?

Thank you for insight!

 

[amberwolf]

I can't access the link, but most likely the BMS in the battery is shutting down under load to protect the cells.

To find out why, you'll have to open up the battery and measure the voltage of each cell group. The group that is significantly different (lower) than the others is likely the issue.

However, most likely the battery will operate almost normally once it's been recharged and left on the charger to balance for a long enough time (which might be days or weeks if it's far out of balance). It'll still have the lower-capacity/weak cell group, and so it'll still have the same problem under higher loads (especially as it gets less full on a trip).

If that's the case, to really fix it you'd have to replace the cell groups that are problematic. (or replace the whole battery).


As for the present 41v on the battery terminals, it doesnt' mean too much to readers until you also tell us which chemistry it is and how many series cells in there. Or what the fully-charged voltage normally is, or what voltage it normally cuts out at, etc.

 

[Spesseh]

What I know is that the battery is a 10.4ah battery with Samsung 2600mAh 18650 cells.

If the battery had bad cells shouldn't it still be possible to turn on the display?
When I turn on the battery when it is connected to the drive there is a "click"/"tick" sound about one second after power on. No such sound when turning on the battery as long as it is disconnected from the drive.
I checked the windings and they do not look burnt.

Today I also tested with two other batteries and the drive did not power on. So I don't think it is the battery. I have changed the controller too.

Any other things that could fail on the BBS01?

 

[amberwolf]

What I know is that the battery is a 10.4ah battery with Samsung 2600mAh 18650 cells.

Unfortunately that leaves out the only information we actually need to know about the battery for this problem, which is what voltage it *should* be at (what it's full voltage is, or it's empty voltage, or what it's number of cells in series are, etc).

If the battery had bad cells shouldn't it still be possible to turn on the display?

Not if the BMS shuts off the output of the battery to protect the rest of it because of the low cells. You can get a "ghost" voltage on the output that persists until you put even a tiny load on it, so it would appear to be ok until you turn on the bike and it's voltage would then disappear.

Today I also tested with two other batteries and the drive did not power on. So I don't think it is the battery.

If the other batteries are of the correct voltage to work on this system, and they also work on other working systems, then that would be a valid test. If the other batteries aren't known to be the right voltage for this system, and they are not verified as working right now on another system, then it doesn't tell you much.

 

[d8veh]

The battery behaviour indicates a short in your system somewhere. Normally, I'd say blown mosfets in the controller, but you say you replaced it. It's possible that when the mosfets blew the first time, the resulting permanently open gates burnt the motor windings.

I'd take the controller off and measure the windings' resistance, and check continuity to ground.

Before doing that, you could disconnect the controller from the motor and then see what happens when you press the switch on the LCD. If it stays on, you know the problem is in the motor windings.

If it doesn't stay on, it could still be burnt motor windings that caused the second controller's mosfets to blow, so you'd need to test that by measuring on the controller the resistance between each phase wire and the battery positive, then each to battery negative. Each group of three readings should be the same as each other and in the range 7K to 15K.

 

[Spesseh]

Excellent. Thank you for sharing your insight. I will make some additional measurements tomorrow and see if I can find where the problem lies.

Thanks.