Bafang BBS-HD speed sensor problems...

Hi Folks,
Just seeking some inspiration and guidance re a speed sensor problem I've encountered with my new BBS-HD. First I should stress that I've searched the ES forum (and elsewhere) several times and read up on various fixes involving reorientation of the sensor body, shortening the cable etc. I have also ofcourse contacted EM3ev from whom I purchased the drive. They've responded quickly and have already made some diagnostic suggestions - I'm confident that ultimately they'll be able to help me out. I guess I'm raising the issue here just in case I've missed something obvious that the collective wisdom might be able to identify. EM3ev have also suggested that I check that the sensor is working, but I'm unsure of the pin-out at the sensor body - maybe someone can clarify this for me?

The drive is set up on my Surly long tail. The problem is that:
- after the drive has operated for a few seconds - whether throttle or PAS - there's a beep and an error message appears ('21H') and it stays on until the drive is turned off
- the computer's speed display simply doesn't work (which is what the error 21H implies)
- as soon as the 'ignition' is switched on at the handlebar the red LED on the sensor comes on and stays on whether the wheel is spinning or not (heh LED stays on irrespective of interaction with the wheel magnet).

I have another BBS-01 so I know how the sensor is supposed to operate. In normal operation the LED flashes when the wheel magnet passes by the sensor body. In my case the LED is on constantly. The sensor has a 3-wire cable and I presume that these consist of 'signal', 'ground' and 'power'. Because the light is on all of the time I'm guessing that there is a 'short' of some sort between the power wire and one of the others (I'm not sure how these things work! Whether that 'short' is somewhere in the cabling or maybe in the controller itself is unclear.

I had a few spare parts so to try to isolate things I've:
- swapped the sensor body with a spare and also...
- swapped out the 'extension' cable that connects the motor side of the cabling to the sensor body.

Neither of these strategies made any difference - the LED stays on all of the time and the speed readout remains inoperative. This suggests to me that the sensors I have are probably both OK and that the problem is either between the screw-together mid-cable connector and the controller body, or perhaps in the controller itself. Do others come to the same conclusion? Have I missed something?

In an earlier ES forum discussion it was suggested that horizontal (rather than vertical) orientation of the sensor might be a problem. I tried hand-holding the sensor vertically close to the magnet as it rotated - again no joy! In fact the LED comes on with the ignition, both when I'm holding the sensor right off the bike and when it's mounted on the frame.

Joseph at EM3ev has suggested that I test the sensor and it's cable with a multi-meter. Can anyone tell me what the pin-out of the sensor body is?

Any other suggestions or solutions would be welcome. As I've said, I'm confident that EM3ev will resolve the matter on the long run - I'm just keen to try to understand the problem myself and maybe find a solution that doesn't involve too much hassle...

thanks,
Sam.

If the LED is on, then the sensor is getting power. It has to blink when the magnet passes by. Maybe your magnet is too weak? The orientation of the magnet matters too. I would try using a loose magnet and see if you can get the LED to blink off by trying different orientations of the magnet. If you have a bigger magnet around, try that too. It seems unlikely you would have two bad sensors that light up, but it's always possible.

fechter said:

If the LED is on, then the sensor is getting power. It has to blink when the magnet passes by. Maybe your magnet is too weak?..

Click to expand...

Brilliant! As I said, all I needed was some inspiration (and a bit of wisdom!) I think my uncertainty lay in understanding how the magnetic switch worked - it's obvious now that it's 'normally on' and the passing magnet just turns it off momentarily, interrupting the power flowing through the LED to ground.

A scrap of super-magnet waved past the sensor at close range did indeed induce a flicker in the LED and a reading at the computer screen. So it seemed that I simply did not have the sensor close enough to the wheel magnet! I've moved the sensor to within about 2mm of the magnet and it now seems to work with the rear wheel up on the stand. No '21H' and the speed climbs progressively with acceleration.

Interestingly - with the wheel up and spinning freely, the speed readout cycles very quickly up to about 60km/h, and then - if the throttle is depressed further - it starts again from 0km/h! FWIW it may also be worth noting (and confirming earlier posts on the subject) that orientation does seem to be important - the sensor does indeed need to be horizontal. In my case I found the magnetic switch would not work with the sensor barrel oriented vertically.

Thanks for your help Fechter. For some reason (possibly lack of brainpower) I find it quite easy to get a bit daunted by even the simplest of electronic problems and it's reassuring to have such a friendly and helpful resource as ES at hand. I'm looking forward to a test ride later today!

Thanks again,

Sam.

OK, glad that worked out. If you had a bigger magnet, it would work with a larger gap.