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Bafang Bbshd shift sensor inop

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    Bafang Bbshd shift sensor inop

    Shift sensor stopped working. Assuming it was the sensor that failed, I replaced it with new. Still inop. Suggestions?

    #2
    The shift sensor needs power from the controller to operate. It could be yours is getting no power. If you have a voltmeter or care to invest in one you could probe the female side of the 3 pin shift sensor connector to check for voltage. If you find no voltage there or incorrect voltage then you might suspect damage to the cable feeding the shift sensor, trouble in the controller or other causes.

    I've attached a wiring diagram for reference. The bottom box on the righthand side shows the pinout for the female half of the shift sensor connection. It shows the correct wire colors but unfortunately I don't know for sure what voltage you can expect at which pins. I suspect pin1 (red) is +5vdc, pin3 (black) is ground and pin2 (white) is signal.

    I suspect on a working unit one would read +5vdc across pins 2 and 3. I have probed the connector on my BBS02B and get 0 volts but I have some problems with my controller and suspect it isn't feeding the shift cable any voltage.

    I have asked here what the voltages should be but either nobody knows or else they just don't want to say. Or maybe they just haven't found time to respond, can't say for sure. It would be interesting to hear what readings you get. It would provide some clues for everybody.

    If you do probe the connector then be very careful to not short the pins. If you need advice on how to do it safely just ask and I will explain how I do it.

    Click image for larger version

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    • AltaBrad
      AltaBrad commented
      Editing a comment
      I got an answer back from gearshift.com. Using the pinout diagram I posted above for reference:

      pin 1: power, 5vdc 
      pin 2: signal, should be same as pin 1 or slightly less so about 4.75vdc
      pin3: ground, 0vdc

      The controller monitors the voltage on pin2. When the gear sensor detects movement in the shifter cable it shunts pin2 to ground through a resistor which causes pin 2 voltage to go 0. When the controller sees 0vdc on pin 2 it cuts power to the motor.

      When the shifter cable stops moving the sensor allows pin2 voltage to go high (about 4.75vdc). When the controller sees the voltage go high it restores power to the motor.

      The brake levers work the same way except unlike the gear sensor they don't need +5vdc power to operate therefore they don't have a red wire. Brake levers are just a normally open switch. They have only a signal wire at about +5vdc and a ground. When you apply the brake the switch closes and shunts the signal voltage to ground which causes signal to go low (0). Releasing the brake lever opens the switch which disconnects signal from ground and allows signal to go high. When the controller sees high (+5vdc) on the signal wire it restores power to the motor.
      Last edited by AltaBrad; 03-02-2022, 12:15 AM.

    #3
    This old thread might help.
    Seems there is only one gear sensor manufacturer, gearsensor.com. User manuals on their support page says the gear sensor should flash red twice when the system powers up and once when changing gears.
    I've contact them to inquire about connection pin voltages, waiting for reply.
    Last edited by AltaBrad; 02-24-2022, 12:08 PM.

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      #4
      There are more options now. Some look like the gearsensor at least on the outside but may not be the same inside. There are also at least 2 other styles that look different too sold by dozens of vendors now. If you have a genuine gear sensor they seem to be very reliable. Anything else can be hit and miss quality wise. The genuine ones tend to sell in the $50 range. If you paid less you likely didn't get a genuine one and may have got a poor copy that maybe never worked.

      Comment


      • AltaBrad
        AltaBrad commented
        Editing a comment
        Thanks for that info. You mention genuine. Is that a brand name? If not then how does one tell a genuine from the rest... by price alone?

        My $15 one worked great until it got smashed and the little wheel inside got lost. Crud off the road and shift cable gets into them and gums up the wheel inside. They need to be disassembled, cleaned and lubed once in a while.

      • 73Eldo
        73Eldo commented
        Editing a comment
        I was considering gearsensors.com to be the genuine ones. They seem to be well built and reliable and last time I looked they were in the $50 range.

      • AltaBrad
        AltaBrad commented
        Editing a comment
        I thought maybe that's what you meant but wasn't sure. Thanks for the clearing that up.
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