New e bike conversion PAS knowledge needed

Electrically assisted bikes, trikes, etc.
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fixerupper
Posts: 45
Joined: 28 May 2018, 2:06pm
Location: Crete Greece

New e bike conversion PAS knowledge needed

Postby fixerupper » 5 Sep 2018, 12:20pm

As some of you know ,I recently fitted a 250/500 watt rear hub motor complete with a 36 volt 11amp hour battery , PAS sensor, SW900 LCD and thumb throttle to my Specialized Rockhopper MTB …the bike works fine on the thumb throttle and I can buzz about the tracks and dirt roads here no problem, but the PAS system seems to have a problem.

The motor starts but cuts out as speed increases, making smooth travel very difficult. In PAS 1 eco level the power comes on at about 7 kph/4 mph and stops at 9 kph/5.50. In PAS 2 std level the power will continue up to about 11 kph and then fade out … and so on up through the PAS levels. In PAS 5 power the speed will get up to about 15 kph. This effect is altered slightly with gear changes. It is impossible to reach the designated speed for this motor, which I think is about 22 kph,15mph using the bike in PAS mode though all goes smoothly just using the thumb throttle. Anyone know how to stop this happening in PAS mode?

An question for the techies ..The motor is 250/500 watts dual wattage. I'd really like to find a way can you shift the settings so you know that you are legal (250w only) for road travel? Also the SW900 LCD shows the wattage varying widely from as little as 75w to 800+ - how is that possible if it is only a 500w motor?

I mounted the PAS sensor on the chain-ring side of the bottom bracket because there was’t enough space between the frame and the crank. The gap between the magnets and the sensor is about 2 mm. Is the fact that the back of themagnets are against the granny cog affecting the magnetic field that the sensor reads? .....the other thing that just pops into the what I call a brain is... do I need a torque sensor instead? sorry for a long post ..jeff

hemo
Posts: 474
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: New e bike conversion PAS knowledge needed

Postby hemo » 5 Sep 2018, 11:46pm

Controller rating varies each pas level will have a different power/amp %.
All are approximate.
Pas 1 13% or less hence why you see 75w or so.
Pas 2 20%
Pas 3 33%
PAS 4 50%
PAS 5100%

The reason you see 800w or near is the voltage x amp output.
Although controller says 11a it will deliver double at 22a in Pas 5 or on throttle if fitted.
So volatge 36v nom x amps 22 = 792w.

Magnet affect on chain ring will have little or no affect on sensor signal, if signal is poor make sure magnet ring is facing the correct way for magnet polarity strength.

Magnet/sensor gap 1mm.

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fixerupper
Posts: 45
Joined: 28 May 2018, 2:06pm
Location: Crete Greece

Re: New e bike conversion PAS knowledge needed

Postby fixerupper » 6 Sep 2018, 3:57pm

Thanks for that info hemo...My controller is labeled..current 22plus or minus 1A....and the battery is 36 volt 11ah 2200WAH li-on so I guess I should watch the watts on the hill and pedal more ... I'm going to remove the disc from the back of the small cog and re-mount it on the face of the four flat screws that fasten the cog on ...that will make it possible to with a re-designed bracket to mount the sensor much closer to the disc. we will see ..thanks again ..

hemo
Posts: 474
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: New e bike conversion PAS knowledge needed

Postby hemo » 6 Sep 2018, 8:54pm

11ah usually suggests the cells will most likely be Samsung but which cells ?
Are they mediocre 22F 4.4a rated or 22P 10a rated, there is a big difference in performance.
Cell sleeve colour is a pointer as is the marking on th sleeve.

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fixerupper
Posts: 45
Joined: 28 May 2018, 2:06pm
Location: Crete Greece

Re: New e bike conversion PAS knowledge needed

Postby fixerupper » 9 Sep 2018, 10:50am

OK here's a thing ...after re- positioning the PAS ring and sensor it's now 1mm I was hoping when I went out today for a 6 mile ride I would be happy with the set up ..well it worked OK but I still find it very lumpy ... it's workable on the flat but if I speed up peddling because there is a rise in the road the power goes off . On the very hilly bits around here even when I try to keep a steady rhythm...it seems very unnatural ...Half way around my morning jaunt I was thinking about the eight magnets wizzing past the sensor ...I guess the sensor is counting the gaps and relaying that to the controller, you have a choice of 5,8,or12 magnets ...so I stopped and re-set the control box for twelve magnets ...and it 's made it so much better ...the power comes on and then tails off smoothly I can control the wattage by peddling faster ...very satisfying to see the speed going up and the wattage going down .....so has anyone else done this ? is this going to damage the controller or any other bits of the system ? If I swap the eight magnet sensor for a twelve ..will that improve things even more ?..looking forward to hearing the thoughts of the hive mind ...jeff

hemo
Posts: 474
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: New e bike conversion PAS knowledge needed

Postby hemo » 9 Sep 2018, 10:50pm

It depends on the controller software/programming.
My pas doesn't work smoothly if magnet count is wrong with KT controller. I had a 12 pole disc and controller was set to read 10 and didn't deliver power properly, changed controller to read 12 poles and all worked perfectly.
I can only assume that the timing frequency between poles can be read by the controller software so the controller knows how many poles there are.