Rear hub motor issues

Discussion in 'Electric Bicycles' started by fsroque, May 11, 2018.

  1. fsroque

    fsroque Just Joined

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    Hi,

    I have a Bafang rear hub motor SWX02 with a Bafang controller and the c961 lcd. The motor is 250W 36V and I have a 11.6ah battery pack.

    A couple of weeks ago the speed sensor failed, there was no signal coming from the motor. I opened up the controller and installed an external speed sensor. The problem is that the motor feels weaker somehow. The peak torque is somewhat lower, and the walk assist function is almost useless.

    I had an old kt controller and lcd lying around and tried replacing the bafang one. Seems like the walk assist packs a bit more punch, but degrades quickly after running for 10 seconds or so. Is this normal? I wanted to replace the controller completely to test the motor on a normal trip, but I can't seem to get the motor running from the kt controller other than by using the walk assist function. Connecting the PAS sensor (the original one) does not start the motor. I don't have a throttle to experiment with, but I connected a 1K potentiometer to the KT throttle cable and I am able to pass 0-4.5V through the signal cable, there is a little spinning square in the lcd on the 1-4V range, then I get error 1 at the top voltage. I assume the error is normal, but I am worried the motor won't start. P1 is set to 87 and P3 to 1. The controller is sensorless so I am only using 3 cables to the motor.

    My questions are:
    1 - does this seem a motor or controller issue?
    2 - anything I can do to hook up the KT controller + lcd?
    3 - suggestions for motor alternatives? I was considering changing to a mid motor, keeping the 36V battery. Something like a Bafang 8FUN BBS02 500w 36V. I would link to the pswpower.com item but the site seems to be down. There is also the size of the chainring to consider. I'm not sure I have enough clearance to install the mod drive either.

    The bike I have: https://www.cargobike.se/produkt/cargobike-classic-electric/ . It's 50kg, I usually ride it (I'm 90kg) with two kids on the front (about 40kg extra). Hilly area, I don't mind pedalling, but could use more power than the current 250W. The bike should not go faster than 30km/h.
     
  2. With the Bafang controller, it's possible that the speed sensor is faulty. It could be dragging down the 5v due to an internal partial short circuit, which would interfere with other functions of the controller. The sensor is easy to replace. It's an SS49 that costs nearly nothing. You take the side-plate off the motor and it's directly underneath.

    With the KT controller, are you sure that you connected your potentiometer to the throttle connector? I don't see a symbol when I use mine.

    It's possible that you have a wrong setting for the throttle. There's one where you set its priority. IIRC, it shows a symbol when you set it so that it will only work when pedalling (non zero start). You need it set to zero start.

    When you get it working with the throttle, you will most likely need to change the settings for the PAS until it works correctly.

    The faulty sensor shouldn't be a problem with the KT controller because there's no connection.
     
  3. fsroque

    fsroque Just Joined

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    For reference I had to change the C1 setting in the KT controller to 05 for my PAS to work.

    I could not make the throttle work by using a potentiometer, using any of the P4 or C4 settings. It's non-important since I'll use the pedals to start anyway.

    The bike definitely feels snappier with the new controller so I'll continue the remaining connections. Still have to solder some adapters for the harness I have connecting to the lcd and ebrake.
     
  4. fsroque

    fsroque Just Joined

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    Hi again,

    I managed to break the lcd while installing the KT controller so I haven't been able to run the bike with it.

    I have been running the bafang controller with an external speed sensor, but since the controller only supports minimum 6 magnets for the speed measurement I get 1/6th of the speed on the screen.

    Yesterday the motor started making strange grinding sounds after running for 10 minutes or so. If I stop for a few minutes the noises go away, only to come back again after biking for a while. It seems they come when I am stressing the engine more. Could this be related to overheating due to the controller having the wrong speed measurement?

    I would like to take up point 3 from my first post again, would this be a good motor for replacing the existing? http://www.pswpower.com/peng/iview.asp?KeyID=dtpic-2014-8S-T0WE.955GT
    And the 44T chainring?

    Thanks
     
  5. I can't see that the motor noise is in any way related to the speed measurement. Check that all the connectors are tight.
     
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