Incorrect voltage readings won’t let motor run.

[Raymond]

Hi, I’m new and probably not the best at e-bike repair, I have a Bafang BBS02 500w motor, with a 48volt 17.5 Ah 840Wh battery
when I put in the battery it says 41.4 volts. But the same battery in my other bike, the one that works… says 54.4 volts and it works fine in the other bike,
My question is, is this a repairable problem? Is it possible for an electric motor novice to make such a repair? The battery and motor are almost new.
My thanks for any advice

 

[E-HP]

I’m guessing it’s not a talking battery, so what “says 41.4v”?

 

[docw009]

You must be reading the voltage off the bafang display. Is it an 850C?

The same battery reads 41.4V on one bike and 54.5V on the other. Do you own a voltmeter, so that you can check the voltage independently?

If the battery really is at 54.5V, it's almost fully charged. What happens if you put the charger on the battery? Will it start taking a full charge or will it shut off right away?

 

[Raymond]

Ok, thanks, I put a volt meter on it and I get 53.9 so then I put it back on the charger, and its charging, just until it is topped off I expect,

 

[Raymond]

Yes, you are correct, I was reading the voltage from the display on the bike.

 

[E-HP]

The battery and motor are almost new.
My thanks for any advice

Did they work properly together when new?

 

[Raymond]

Yes, they worked beautifully, until the bike was overloaded. A friend used it and did not shift as he should have.

 

[E-HP]

Yes, they worked beautifully, until the bike was overloaded. A friend used it and did not shift as he should have.

I was thinking it was the display (I was going to suggest resetting it), but given that scenario, it seems like it could also be controller related.

 

[docw009]

Overloading the motor isn't going to hurt the display. What ever voltage it reads is probably correct, There should be a straight shot from the battery thru the controller to the display's power lead, and you have a 13 V loss in it. Maybe a connector is half melted.

Inspect your battery connections if you used a plug-in battery cradle. Also check whatever you used to connect the controller power leads to the battery,

 

[Raymond]

Thanks, I’ll take all the connections apart and check.

 

[amberwolf]

Yes, they worked beautifully, until the bike was overloaded. A friend used it and did not shift as he should have.

An overloaded controller could fail in a way that draws more current than the battery is meant to allow. When this happens the battery BMS shuts off, and will just have a "ghost voltage" on it, but normally that would just drop to nothing immediately and the display turn off because of the controller fault.

If that's not happening, the tiny transistor inside the display that turns the controller on may be damaged, keeping it from turning on the controller, so that the controller does not load down the battery. Does the voltage keep dropping, or stay at that specific voltage no matter how long you leave it plugged in to the bike and turned on?


If the connectors for battery to system aren't fully connecting, then the tiny load of the system just being on could cause a voltage drop. Engaging the motor would then turn the system off because it wont' get enough current to run.

 

[Raymond]

The voltage reading stays at 41.4 even after waiting for about half an hour, it shows there is no charge on the battery… even though the battery works perfectly in my other bike, it seems you are on to something with the controller problem. I purchased a duplicate display, but as you know, that didn’t fix the issue,
my sincere thanks for your help.

 

[docw009]

I have verified this measurement on my own BBS02B. I unplugged my battery. Be sure the battery is completely disconnected for these continuity checks. Turned on the display to discharge the capacitors on the lines. Unplugged the display.

Then I checked continuity between the ground pin on the BBS02 input and the ground pin on the display connector. DId the same on the corresponding power pins. Both are straight thru wiring, as expected, and effectively zero resistance.

The bottom figure is for a BBSHD, but the BBS02 is the same.

You could also measure the display connector with the battery attached, but if the display reads 41V, I think the meter would also do the same. It;s also a tricky thing, trying to put a meter probe om the power pin without touching the adjacent data pins and blowing them up. I only do that when I can find my jumper wires to slip over the pins,

 

[Raymond]

I’m not sure if I am giving you the correct information, but I checked continuity between the ground from the battery through each Connection ,they all appear to be brand new. then I checked the ground through just the motor assembly and I have resistance on that line my meter was set at 200 oms and the reading was 153.4 plus or minus as it fluctuates.
is it possible to just buy the controller? Or do you have any other suggestions?

 

[docw009]

BBS02B controllers can be purchased. Here's one seller that I've used. You might find it for less and with better shipping elsewhere on aliexpress.com. This video shows you how to change it,

150 ohms is significant and suggests a half broken ground wire in either the power cable coming in, or the main harness coming out. There is also a ground in the speed sensor connector. Pinout appears below, thanks to Tommycat, a poster on this forum. You can check that continuity from the "black" to either of the grounds on the other two cables. It might isolate the problem to one side,


I assume the problem will be on the power cable because that's the only one that can get hot. There's a possibility it got pinched where it enters the motor. It's potted in silicone.


BBS02 enthusiasts have dug out the silicone to get access to the circuitry underneath. Here's a picture.

If you want to try to save the controller, you could do the same to expose the cables and see if there is a broken wire that can be repaired. Me, I'd spend the money for a new controller.

 

[E-HP]

I’m not sure if I am giving you the correct information, but I checked continuity between the ground from the battery through each Connection ,they all appear to be brand new. then I checked the ground through just the motor assembly and I have resistance on that line my meter was set at 200 oms and the reading was 153.4 plus or minus as it fluctuates.
is it possible to just buy the controller? Or do you have any other suggestions?

Did you check continuity between the red controller battery input wire (with the battery disconnected) and pin 1 (P+) of the display connector?

 

[Raymond]

Well… I have now, I have an open line between the red motor input and P+