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Help with Speed Sensor

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    Help with Speed Sensor


    I put together my first E-Bike with a Bafang BBS02 Kit. For the most part it seems to be working great :).

    However, I am having an issue with the speedometer on the display. Sometimes it shows a speed and sometimes it doesn't.

    The magnet and sensor seem to be working because it shows a speed when: 1) I wave the magnet across the sensor by hand or 2) when I use the throttle and the motor is supplying power to propel the bike.

    But the speedometer shows no speed when 1) I am just pedaling with electric assist and 2) when I use the throttle but the motor cuts out because the speed is too high.

    Is this normal? Or is there a known solution to this problem.

    Last edited by sparshk; 10-07-2021, 08:25 AM. Reason: Throttle

    Have you experimented with different alignments of the sensor and magnet? Sometimes they have to be very square to each other and very close like within a mm or two. The stock bracket is kinda flimsy and I wonder if maybe your bike has some flex to it so the crappy bracket and the flex in your bike are just not holding the alignment well when you are pedaling. Are you sure your crank arms arms or your body or shoes are not hitting the sensor or wires? Are you sure the wires are not being pinched between the motor and the bike frame?

    Do you have or know anyone with a 3d printer? Some people have come up with some much nicer brackets than the stock one.


      Thanks 73Eldo!

      I think that must be what was going on. I moved the sensor incredibly close to the magnet, as close as possible without touching, and it is working!

      I am working on a steel frame xtracyle and and exerting pressure on the pedals must cause more flex on the frame then the motor.

      Happy riding (well as soon as its the weekend :)


        Move the magnet and sensor closer to the axle to increase the magnet dwell time by the sensor. If the magnet is too close to the rim it goes by the sensor so fast it isn't seen by the sensor.


          One other thing that can help in sensor pickup is adding a very powerful aftermarket earth magnet to the supplied magnet that comes from Bafang. The supplied magnet is very powerful and is probably rated as a rare earth magnet, however, in my case even with very close magnet placement, I was getting some PAS cutout that I couldn't completely eliminate. Online I found some highly rated rare earth magnets in the same face size as the Bafang magnet and attached one to the Bafang magnet. I'm no scientist by any means, but this act of having two magnets stacked apparently improved the signal to the sensor even though the distance between sensor and magnet(s) didn't change.

          This adds one other benefit. In off road terrain with a good deal of vegetation, the sensor can occasionally get pushed over a bit to make contact with the spoke magnet. With two magnets stuck together, the added magnet gets pushed off the face of the Bafang magnet, and the sensor doesn't get hammered as hard with contact before you figure out where all that clicking noise is coming from. The added magnet is usually still in the area...sticking to a spoke, brake rotor, etc. In my application there is no room for the loose magnet to get jammed in the caliper/pads to cause a problem...just something to look at for safety's sake. I carry a spare magnet just in case the added magnet has left the area...LOL!