PAS boffin help

[jeff St.Clair]

HI new member here .
I just 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 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 and stops at 9 kph. 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, using the bike in PAS mode though all goes smoothly just using the thumb throttle.so why is this happening in PAS mode?


Another question. The motor is 250/500 watts dual wattage. can I alter the settings so I know that I am 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?


Also 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 the magnets are against the granny cog could be affecting the magnetic field that the sensor reads? sorry for a long post but it a train of thought post ...any help much appreciated ...jeff

 

[Benjahmin]

Check to see if pas disc is actually rotating smoothly when you turn the peddles. I had one that would intermittantly slip on the shaft, causing power to cut in and out. Is the pas disc/sensor gap constant? A variable gap can give problems.
The motor will consume whatever wattage the controller throws at it. So a 20A max controller will be 720W. This has nothing to do with the rating of the motor. That is merely it's continuous rating, i.e. the wattage it can run on for 1 hour continuous without over heating. Don't know what they mean by dual wattage motor. Sounds like marketing B.S. to me. For legality you need to look and see how the motor is labelled. If it's labelled 250W, no problem. What it actually consumes is between you,the controller and the battery range gods.

 

[jeff St.Clair]

Yeah thanks Benjahmin the pas disc is firmly fixed to the back of the granny cog and the gap is a constant 3mm...Im thinking that may be the granny cog has become magnetised so the sensor in unable to read the speed of the crank do you think this is possible ? the Motor is not labelled with any wattage just a ce sticker ....so is riding with a wattage of 700 or 800 is OK , the label on the controller say current 22 plus or minus 1A...thanks ..jeff

 

[Nealh]

3mm gap from pas to sensor is too much it ideally needs to be closer to 1mm.

 

[Benjahmin]

This law on motor rating is bonkers. AFAIK to be fully compliant you need a label with manufacturers name and rating of motor. That said, who's gonna look? You could get some cheap letter/number stamps and just stamp it '250W'. 'That's how it was sold to me officer' , not that ones ever likely to ask.
So, yes, it's perectly legal to run at 800w, if your battery can handle it.

 

[jeff St.Clair]

I don't think anyone is going to worry about the legal stuff here in Crete. My question was really about the battery and controller and if it would damage them....

 

[Benjahmin]

Gotcha.!
The controller can only deliver what it is designed to deliver, so if that's 800w at max then it should be OK with that. The battery, however, needs to be able to deliver the maximum amperage that the controller calls for. This may not be the case. It very much depends on cell rating and quality.
Most batteries are 10 cells in series to give 36v. Then, 10 cell strings are parralleled to give capacity. So a battery made of cells with a rating of 5A, with 4 strings in parallel is theoretically capable of delivering 20A. 800w at nominal 36v is 22.22A - battery will struggle and will be damaged by repeated use.
5 strings of 5A cells would give 25A capacity, better but still a bit close to call. Ideally the battery would be capable of delivering 1.5 times the max rating. So for 800w that's 33.33A.
What's your battery rating? What type of cells? And can you trust what the supplier has told you is in there?

 

[jeff St.Clair]

Right thanks for that Benjahmin ...the only info I have on Da Battery is 36 volts 11 amp hour 2200MAH li-on Battery ..so 36x22 792 ...so I need to watch those amps on the hills with this battery... what about the PAS problem ? in the morning I'm going to take the disc of the granny cog and bond it to the cog fastenings that will make it possible to re-position the sensor and close the gap to 1 mill...

 

[Benjahmin]

OK so that's a 10s5p battery. 10cells in series, 5 strings in parrallel. What this doesn't tell us is the current rating of the cells or make or type. If you can put up a picture of it someone may know.
36v 11Ah is only a 396Wh battery. That's actually quite small, especially for hilly terrain. Most e-bikers will consume between 10 to 20watt hours per mile. It sounds like you may be at the upper side of this. However, a 396Wh battery used at 10Wh/mile gives a range of 39 miles, less at higher consumption.

Just re-read your op. My bike has the pas ring bolted in place of the granny ring. I actually drilled two holes in the pas ring to match two of the mounting holes, it works fine. However the gap to the sensor is only about 1mm. Are all the connections between sensor and controller OK? Are the symptoms you describe exactly the same each time or are they intermittant/variable.
I too hate things that don't work as they should, it's frustrating.

 

[jeff St.Clair]

Right ...I have re rigged the PAS sensor there is now 1mm between it and the disc , the sensor is pointing the right way and the disc is rotating in the right direction .I went through the whole setup all the connections are firm ...I also fitted the brake sensor on the back brake and that is working .I tided up the cables and went for a test ride ...not over impressed the PAS kicks in ok but only for a short time it's like the parameters are very narrow, too slow and it wont come on.. too fast and it cuts off .Either side of about 14kph so the bike will not run smoothly ....I can over come this with the thumb throttle but this whacks up the watts to 800 on the LCD...any one got any tips about fine tuning or hacking the SW900 on a system like this ....

 

[jeff St.Clair]

This is a photo of the plate on the controller and the Battery ...[ATTACH]26703[/ATTACH]

 

[jeff St.Clair]

OK here's a thing ...after re- positioning the PAS ring and sensor 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 ...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

 

[wheeliepete]

You won't cause any damage running like that, it's only a signal the controller uses to supply power to the motor. You could try a 12 magnet sensor, as this may improve things further. I am not familiar with your display, so can't advise on any other settings to change.

 

[jeff St.Clair]

Oh thanks for responding wheelie ...that's good to know ...it's what I thought but nice to have it confirmed ...