Bafang CST 180mm vibration/resonance at low revs when using KU93 controller

[jonathan75]

Hi all,

I've just installed my KU93 but there's a slightly disconcerting resonance/vibration at low revs on the Bafang CST HT 250w. After I discovered this, I tried using the self-learn cable, but all that happened was it automatically span the motor (gears?) without the motor itself spinning - disconcerting.

Would anyone know if this vibration at low revs is just a known characteristic of the KU93 and if my best bet is to ignore it?

Thanks

Jonathan

 

[Deleted member 4366]

It should be smooth. Do you have the hall sensors connected? If so, disconnect them and see if it's any different.

 

[jonathan75]

It should be smooth. Do you have the hall sensors connected? If so, disconnect them and see if it's any different.

Thanks D8veh. I've tried that now and it was the same. It's just a bit boomy and resonant at the low revs, do you know what I mean, making a sort of whoop noise? It's not actually rough per se. It's just noisier than the 6 fet 14a compact controller I'm used to, and makes the motor whine at higher revs.

Other odd things. Max 15mph without the speed limiter (old 14a controller would do 22-25mph!). Attaching the white speed limiter wires makes it go about 8mph tops!

The throttle ramps up so slowly you can barely notice it accellerating. Not great in traffic.

And, scarily, the cruise control isn't cut off by using the brakes alone (although this may be because I blew up the LED display and had to short the red and blue wires on the LED connector to make the controller run).

Bit of a shame really, I had high hopes for it.

 

[Deleted member 4366]

There's lots of versions of the KU93. I've only had the KU93s without the connector for the LED panel, but if it's the same as the KU65, the PAS will default to level 1 without the panel connected. The throttle should be unaffected.

You should also look at the three-speed switch connector. With nothing connected, operation is normal. With the middle (black) wire connected to one of the other two, the speed will be restricted. With it connected to the other, you get a sort of overdrive, which will increase the speed above what's normally possible. The overdrive only works with the hall sensors connected.

If the controller detects a problem with the hall sensors, it might default to sensorless operation. You can use the three-speed switch boost to test which mode the controller is in, sensored or sensorless, by whether it boosts or not. You open the throttle to max wih the wheel of the ground. When you bridge those pins, you should notice an immediate change in pitch as the motor speeds up, or slows down.

 

[jonathan75]

You hit the nail on the head. When I checked the hall sensor wires after reading your post, they were all in a totally different order on the controller connector , to what they were on the motor side.

This disorder of wires is what made my led display blow up earlier today -I guess each company wires its stuff differently.

Moral of story- never assume one part is wired the same way as another part which it is meant to fit.

Thanks for your intelligent assessment of the problem, I very much appreciate it.

 

[jonathan75]

Yes, bridging the pins on the three speed connector does make the speed go up and then down.

 

[Deleted member 4366]

If that extra speed is useful to you, put a switch between those two pins. I used to leave mine permanently connected. I didn't notice any loss of climbing power, but, in theory, the efficiency and power at low speed will be compromised in that mode.

 

[jonathan75]

Oh dear - can't seem to get the PAS to work on the KU93. I've taken a photo of the wiring - the middle wire is a yellow. Would you have any ideas please?

 

[Deleted member 4366]

Which Sensor do you have? Which side did you fit it? Did you check if it works when you turn the pedals backwards?

 

[jonathan75]

Which Sensor do you have? Which side did you fit it? Did you check if it works when you turn the pedals backwards?

I've got the new dual hall from BMS ( this one ), installed on the left, and
and this 12 pole one from Elifebike installed on the right (I haven't taken it off yet until I know the new one works).

Neither PAS works going forwards or backwards unfortunately; I've checked the wiring and the colours match up on the 12 pole (with the controller connector); and on the dual hall, they're brown/yellow/black, meeting up with red/green/black on the controller connector.

The brake cutoffs appear to work properly.

There is an extra wire which I can't explain -I don't know if it could amount to a clue.

Edit - I blew the led display when I connected it when the wiring didn't match up, I am running the controller by shorting two wires on the display connector (red and blue),so I suspect that's why I don't have the pas function. Would trying another display be sensible?

 

[Deleted member 4366]

Those pedal sensors are handed. You might have the left on the right side and the right on the left side. It's always best to test pedal sensors begore you fit them. There's four possibilities if you permutate direction and disk orientation (flip). Try all four and see which one works. Then you can figure out where/how to install it.

 

[jonathan75]

Thanks D8veh. I've now tried both pas sensors on both sides, pedalling in both directions, unfortunately without any luck. I have now added a790 LED display , wired up as in the photograph. I believe the yellow and white wires are for a light and I have left them not connected to anything. Again, this has not brought pas function sadly. I've also included a photograph of the LED display, because I think that the 4 lights lit up might be slightly strange - I would have thought, that they would refer to the motor power actually being used somehow , whereas the wattmeter is showing 1 or 2 watts approx only (at zero mph).

If you have a view I'd be grateful

 

[Deleted member 4366]

There's four combinations between the magnet disc and the sensor: clockwise and anticlockwise and two sides of the magnet disv. Did you try them all?

 

[jonathan75]

There's four combinations between the magnet disc and the sensor: clockwise and anticlockwise and two sides of the magnet disv. Did you try them all?

I've now tried all four combinations on the right side of the bike, with the magnet disc and pedal direction, unfortunately no joy. I would change the side of the bike which the pas hall sensor is on, but it is fixed by an intricate setup and the pas worked alright with the previous minicontroller on this present side. However I have tried the dual hall pas on both sides just now (this one) without any luck. I've also tried doing all this with the throttle unplugged.

I wonder if my my shorting the 3-speed connector or my wiring on the led display has anything to do with it. Perhaps the KU93 is only happy with the 810 LED:BMSB after all say it's 'for the KU65/93/123' and with the 890 they say that's only for the s-series controllers. So maybe there's some compatibility issue going on here. I've just ordered another 810 from BMS but it's in a shipment with a new battery so it might take some time to arrive I hear.

Thank you for your input on this - really appreciate it

 

[Deleted member 4366]

The display in your photo is the 790, which should be compatible. You can check that it's working by measuring the voltage on the green wire. It should be 1v level 1, 2v level 2, 3v level 3 and 4v 6km/h.

Did you check the colours on the wires either side of the PAS connector - red to red, black to black, signal to signal?

You can also check that the controller responds to a PAS sensor by sticking a wire in the red pin and rapidly tapping the other end on the signal pin to mimic the signal from the sensor. Measure that you have 5v between the red and black first.

 

[jonathan75]

Thank you - I'll begin this on Saturday when I pick up my electrical tester, fingers crossed.

 

[jonathan75]

I might have blown something in the controller when the first 810 display blew. It kept shutting down a second after switching on, and then I held down the power button and the 810 heated up and went pop and now just doesn't work (it's fully lit and 'dumb' when connected to the controller). It happened because I'd not checked to make sure the controller side of the connector, matched the 810 wires (it didn't).