BBS01B Error 21

[PASJames]

Recently took delivery of a new BBS01B kit and installed it on a bike. When first test driven the speed sensor worked fine on my C965 display which came new with the Bafang drive. I got speed and mileage readings. I then added a kickstand to the bike and accidentally crimped the speed sensor cable. When code 21 displayed I checked the red light. No red light lighting up on the sensor. The sensor cable was not cut by the crimping but the copper of the black wire was exposed and possibly grounded to the frame? The red and white wires were fine. I repaired the cable and checked continuity of all three wires = fine. The speed sensor still does not work...still getting code 21. The three levels of pedal assist and the throttle work. The error code clears each time I pull the brake lever and shut off the motor.

With the display turned on, I checked the voltage of the red, black and white wires at the female plug end of the sensor cable where it connects to the sensor itself. Black to white = 0 volts. Red to black = 0 volts. Red (negative) to white (positive) = 64 millivolts.

At the suggestion of a forum member at Endless Sphere, I tested voltages of the three wires while connecting my black voltmeter lead directly to the battery pack negative. Red was 5 volts, white was 5 volts, black 0. Then I turned the display off and checked resistance of each wire, again using the battery pack negative as the ground. Red was 26 Meg, white was 6.9 K and black was 0...basically an open circuit.

Can anyone help me??

[max_volt]

The voltage readings don't make sense. If the black wire is indeed ground it should have been the same as from the battery. You may need to remove a section of the cable.
Just checked my HD and found ground and the other two the same, very high.

[PASJames]

The voltage readings don't make sense. If the black wire is indeed ground it should have been the same as from the battery. You may need to remove a section of the cable.
Just checked my HD and found ground and the other two the same, very high.

At the suggestion of another forum member, I connected the battery ground to the black wire of the sensor cable. This, because the black wire appears to be cut somewhere. This did not fix anything.

Can you tell me what your voltage values are? Assuming Bafang uses the same Hall sensor and sensor cable on your HD as on my BBS01B, can you tell me which one is the ground what the voltage values are for each of the three wires, black, red and white?

[max_volt]

I really don't want to go poking around with voltage applied and make a boo-boo. I think that 6.9k is problematic. I can't see the colors of wires nor can I locate a pin-out, but looking into the holes of the cable connector with the flat side down, ground is the left hole.

[HarryS]

PASJ, I was going to suggest you run a second ground wire from the battery negative to the sensor ground, but you said that did not work. Did you see if the sensor lit up?

I would hook up the second ground, and check voltages with sensor connector. I have a BBS02, but below freezing in my garage. Likely I'd break something if I popped the speed control connector under these conditions.

The following values are based on what I see on my external controllers. They typically show 4.5 volts on the external 5 volt power leads for throttle, speed, PAS and motor Hall sensors. The speed sensor inputs is 5 volts. I presume the speed sensor input has a 5 volt pullup, and the power outputs have short circuit protection (EE jargon).

Without the sensor connected, I believe you'll see 4.5V on red and close to 5V on white. WIth sensor connected, red should still be 4.5. White will vary between 0 and 5 depending on proximity of magnet. The LED on my BBS02 doesn't light until wheel magnet spins past the sensor. Then it will only go off if magnet is near. This LED behavior is one thing I don't understand on my BBS02. =

[PASJames]

Thank you all for your helpful suggestions. Fechter over on the Endless Sphere forum gave me instructions that led to the solution. In the end, I removed the Bafang sensor and abandoned the red and black wires of the sensor cable. I then connected a reed switch speedo sensor from an old bike I had sitting around between the battery pack negative and the sensor cable white. As the magnet passes the reed switch it signals my C965 display and I have speed and odometer again. Error 21 has disappeared. For me, who has much less electrical knowledge than most of you, I cannot understand why Bafang chooses to use a Hall sensor/ LED light combination. The old standby reed switch seems so much simpler.

[HarryS]

I see. Either you short circuited the power supply for the sensor, or the sensor doesn't work. Nice work around by fechter. And good on you to execute it!

[max_volt]

I have to hazard a guess and would expect the speed display is no longer accurate. A reed sw and sophisticated hall/latch are not the same. Reed sw can be quite electrically noisy after awhile.

[PASJames]

max_volt-
You may be correct about the speed display accuracy. While riding 18 miles yesterday, we noticed that the repaired bike's display registered lower MPH and miles than my Haibike's display. Of course, even though the Haibike is a factory installation, I have never checked it for accuracy either. Can you explain in layman's terms what sw is. I looked up Hall sensor on the internet, but lack the electrical sophistication to fully understand it's operation. Whereas a reed switch is fairly straight forward.

[max_volt]

The reed sw-itch is old tech whereas the hall is solidstate. There are a lot of hall iterations ie bipolar unipolar and I don't pretend to fully get it all.

[HarryS]

It's just switch bounce. If you run a mechanical switch into a digital input, it's fast enough to count the little bounces of the contacts. A designer can find ways around that if given some money to do the circuitry, There must some debounce going on, because the typical result of switch bounce is higher speed (and hence mileage) and PASJ reports lower. And by higher, I would say 2X-3X.

[max_volt]

If you go by the red led it seems to change h/l state with every wheel revolution. So it outputs 0.5 x rpm?

[bikinfool]

I too have a malfunctioning Bafang Speed sensor throwing a controller error 21. I have a new sensor on the way but have my doubts its the fix as the red led is not lit and no apparent damage to any wires found. Does anyone know if the Bafang two wire brake sensors are reed switches? If so I was thinking of trying one to use as a speed sensor, it uses a Higo connector with two pins……...a reed sensor doesn't need a bias voltage....so the red wire from the controller would not be used. Anyone try this or any suggestions if you think this would work. Meantime I put a cheap bike computer/speedo on the front wheel, the kit I have is the BBSHD mid-drive.

[Tommycat]

Bit of a guide if you haven't seen it.. And I'd like to add that the magnet polarity side matters also.

http://electricbike.com/forum/forum/knowledge-base/motors-and-kits/bbshd/34500-setup-and-troubleshooting-bbsxx-speed-sensor

I know the Bafang THREE wire brake sensors behave like a reed switch using just two of the three wires as evidenced in this thread... (acts like a N.O. contact that closes with magnet removed)

http://electricbike.com/forum/forum/main-forum/trouble-shooting/80662-wiring-ebike-brake-mechanical-to-hydraulic-conversion-solved

If you get into it, would you be kind enough to post the wiring pin-outs and wire colors... I would like to update this diagram for the speed sensor connections. :-)