PAS skips - troubleshooting

Hi all,

I just converted an old road bike to electric, with a Bafang SWXH rear hub motor, a KT 12FET controller with KT-LCD3, and a LI-ion 36V 13Ah battery pack with 20A BMS, 8 magnet PAS sensor. I intend to use the bike with only PAS, in torque simulation mode.
I configured the parameters according to the manual and forum entries, and the whole thing works as expected with a thumb throttle. With the PAS there is a problem, that it constantly cuts off the power to the motor, then after a few pedal revs later it comes back. With P3 set to 1 (torque mode) it has a very nice smooth PAS action at all assist levels, until it cuts off.... With P3 on 0, I can almost use the bike on assist levels 1-3, but this is not the mode I'd prefer... on levels 4-5, when motor W passes like 400W, it cuts out also in this mode.
If I set it to 5 magnet PAS mode, it may be a little better, but not sure.... I also set C14 to low assistance, then it's still a little better, but not good.

Battery voltage is constant and high at about 39V at any loads, the LCD displays voltage exactly as I measure with a multimeter. The ASSIST text on the LCD flashes occasionally, and it somehow seems related to the cut-outs, but I'm not sure, sometimes it flashes, and still pushes. How is this supposed to work?

When it cuts out, the LCD stays on, ASSIST text flashes, motor W indicated as 0. If I push the thumb throttle in this state, it applies power nicely as if nothing happened.

Where should I start troubleshooting? Any ideas welcome.....

thanks!!

Look at the gap betwen the PAS sensor and the magnet disc. It should be about 1mm.

d8veh said:

Look at the gap betwen the PAS sensor and the magnet disc. It should be about 1mm.

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thanks for the idea! the gap was like 2-3mm, now I adjusted to 1mm. unfortunately no change in behavior. I made some test today, and it looks like it cuts out, when I slow down a bit due to a hill, and motor power also goes up to like 500w (ASSIST flashes). it's still ok with the thumb throttle, and easily goes up to 1000w.
Is there an adjustable current limit for the PAS operation? or maybe speed related?

can someone explain me the working of the ASSIST text on the LCD? when is it supposed to flash? I found this on Kunteng site, but I cannot understand the chinglish:

Vehicle boosting：With 6Km/h power-assisting functions, the boost logo flashes during boosting, and riders can use it when driving the vehicle and the vehicle driving is labor-saving and easy;

Grab your magnet disk, and try to turn it on the spindle to see if it's tight. It may be that the disk is rubbing on the bottom bracket, and is not spinning as you pedal.

Avitt said:

Grab your magnet disk, and try to turn it on the spindle to see if it's tight. It may be that the disk is rubbing on the bottom bracket, and is not spinning as you pedal.

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it's tight, and cannot be turned on the spindle. also, not rubbing on anything I wonder if there may be something wrong with the pas sensor itself? I'll get the 'scope out and check the signal, but I'll be unable to reproduce the cut-outs in the garage, as it looks to happen under load only.