Bafang Hydro Brake Switch Issue

TNC

100 W
Joined
May 3, 2021
Messages
167
Location
Texas
I'm loving my BBSHD on my Santa Cruz Nomad MTB. I've had one issue that befuddles me that involves the hydraulic brake lever sensors. I don't see a lot on the forums about these sensors besides people having questions or issues about where/how to mount them. With only a little head scratching I was able to figure out a solid way to position and fix the magnet and the sensor that appeared to work perfectly. The error code symbol comes on at a perfect time and goes off just right when the levers are engaged and disengaged.
Now the problem. At first, the motor stopped exactly as it should with the engagement of the brakes and came back on when the levers were released while riding. After just a few miles, however, the motor quit running for no apparent reason. No error codes and no error code indicating the brake sensors are triggered which would kill the motor as required. The display looks fine, the motor is not hot, and after quite a bit of poking around and inspection, nothing appears to be amiss. For no apparent reason, the motor would come back on occasionally, and the bike/motor would behave as expected...then it would quit again. Believe me, I've disconnected, reconnected, rechecked, and even reprogrammed back to OEM specs all elements of this package...except the brake switch cables.
All obvious and critical components that are required operational appear to be functioning. I am new to ebikes and the Banfang mid-drives, but I'm a bike mechanic and automotive/motorcycle mechanic, so this stuff doesn't seem completely alien to me...though the way the programming elements all come together to provide a smooth power delivery that suits the rider and conditions are somewhat interesting and apparently not always crystal clear to even the highly exposed...LOL! Still, not crazy mysterious from what I've seen reprogramming this package. In fact using much of the excellent direction from many on the forums and internet in general, I've come to a program that I'm extremely happy with for real trail riding.
So, today I was at it again with a dead motor and noticed the brake sensor error light that indicates the levers are killing the motor as required seemed quite slow to go off after the lever was released. This was not normal. I totally understand that as long as this brake switch error code is triggered that the motor will stop. This slow response of the brake error code to go off got me suspicious, so I disconnected the brake sensor cables. The motor immediately came to life. I rode the bike around quite a bit, and the bike/motor all functioned flawlessly. The odd thing to me about this deal is that the motor was dead even when the brake switch error light was off. In other words there was no indication the brake switch was killing the motor...but...it certainly appears to be the case.
I'm at a loss to figure out why the motor is acting like the brake switch(s) are triggered even when the display doesn't show it. The display is a 500C. I'd tend to say the display is working as it should in this regard. I really appreciate those brake sensors when mountain biking as doing a back pedal in most instances isn't always ideal to kill the motor. Now, I will say my latest programming effort has the motor stop quickly when I stop pedaling, but as most of you know it's not an immediate stop like you'd want when riding technical terrain. The brake switches provide that and also let you get back to pedaling quicker without jerkiness.
Anyway, anyone run into this or found a good solution for living with the Bafang brake switches in a less problematic fashion?
 
I have the 500c display with my BBS02 and I'm happy with the brake sensor performance. I have it set it up on the corner of the sensor so it will activate as soon I pull the brake lever (and before I get any braking).

Maybe it's a faulty sensor? There should've been 2 sensors included - you could try swapping them around and see if the issue persists.
 
COAR, thanks for responding. This part is a copy-and-paste from another site that updates this, and I only repeat it in case someone else runs into this odd scenario:

Notice that I mentioned the brake sensor cables were the only ones I didn't disconnect...which was rather short sighted on my part. My initial thought was the shift sensor being the main suspect, but it was fine. I just came back from a ride and found a telling issue that may shed some light. I'll cut-and-paste my findings from another source where a responder may have touched on something.

"Quote other thread"...Rocket, I think you may have hit on something. I just came back from a ride, and while out there I did some experimentation. With just one brake switch cable plugged in, I didn't get any unwanted motor shutdown. It didn't seem to matter which brake switch was plugged in as long as it was just one of them. Plug them both in, and the bike runs fine for a bit, but then the brake switch error pops on and the motor predictably quits. I'm still not quite understanding why the motor was dead without any error light showing in the display earlier. I would think the light would be more predictable.

This is hardly the confirmed long term proof of the issue, but based on its behavior before, it should have shut down during the time of this ride. And the fact that it periodically goes back to killing the motor when you plug both back in seems to indicate some kind of "signal bleed" or such perhaps like you suggest. The good thing is that I can ride with one brake switch which is what I was doing originally. This didn't start until I hooked up both brake switches. I only really need the rear lever switch. Obviously I seriously brake with the front brake for the hard stuff, but I always engage the rear a little or a lot depending on the situation. I may do the voltage check you mention just for more info. Thanks for this insight. You may have hit it.

The other responder suggested looking into the voltage values for both lever switches and that there might be a signal bleed from one to the other with both connected that is not always being read by the display but perhaps picked up by the controller. It's an odd situation, but running on the one brake switch seems to stop any motor shutdown...at least for now.

Well, I've ridden the bike again for a lengthy ride, and the motor has displayed no other cut-off's using just the rear brake lever's sensor cable plugged in. When I get time I am going to look into the voltage feed on both lever sensors, but clearly it appears there is some transient signal bleed when both lever sensors are connected.

COAR, I agree with you that when proper magnet and sensor location are attained at the levers, these sensors work perfectly both during actual riding and on checking the display for the error/braking symbol they exhibit.
 
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