Speed sensor failure

[fsroque]

Hi, I have a cargo bike with a Bafang rear hub motor SWX02 and a bafang controller. During one of my commutes the bike suddenly stopped reporting speed and the display says error 21 and turns off.

I am wondering if the speed is reported by the pas sensor? The controller detects pedalling so pas is definitely working. No red light appears in the sensor (image below). Is it just a case of replacing the pas/speed sensor or should I look elsewhere?

The connectors don't match the extra pas sensor I have here, so I would have to clip the old one and join the cables, don't want to do it unless I'm sure.

Thanks!

 

[Woosh]

the speed sensor is either attached to the chain stay and activated by a magnet attached to a spoke or built inside the motor.
If you don't have a spoke magnet, then it is inside the motor.

 

[fsroque]

Thanks, I guess I can bypass the speed sensor in the motor with an external one, and attach that to the controller. Got one of these lying around: http://www.pswpower.com/peng/iview.asp?KeyID=dtpic-2016-38-4F9M.91FDM

 

[Deleted member 4366]

If you have one of those black sealed Bafang controllers, you'll have difficulty accessing the speed sensor wire. It's the white wire in the motor cable. You also need to connect to 5v and ground wires, which you can pick up from the PAS connector.

If it's an aluminium box controller, you can often get access to the speed sensor wire inside the box where it exits the harness. You can cut it and join your own one there. that might still work with the black box type, otherwise you'll need to strip the outer covering from the motor cable somewhere to splice in your wire.

 

[fsroque]

My controlled is inside an aluminium box. I will need to pull the 5v and ground as well from the PAS connections, right?

 

[fsroque]

I have pulled the speed signal cable, and connect +5V and ground in the controller. I attached the speed sensor and by passing the magnet I can see the signal works. Unfortunately I think the signal is quite weak? By passing the magnet back and forth fast I get about 5km/h in the display. If I turn it more slowly (like if a wheel was turning) no speed is detected. Do I need a more powerful magnet?

 

[Deleted member 4366]

There's a setting (P2) for the number of pulses per revolution. You need it set to 1 and it's probably set to 6.

 

[fsroque]

Unfortunately my display (c961) does not have that option. 6 magnets on the wheel then?

 

[Woosh]

Unfortunately my display (c961) does not have that option. 6 magnets on the wheel then?

you may have to do that if you can't get into the advanced settings (number of magnets).
The alternative is to change the LCD.