Hi, we're new to this forum and i'm asking for some help please. I have an NCM Moscow Plus 48v which although 4 yrs old has just 90 miles on it. last time out it behaved oddly. The power now only comes in pulses every 1 second when i'm cycling which makes it tricky to make any progress. It does it on all power levels. I tried taking off the crank sensor but it was immaculate, i've cleaned all connections with contact cleaner but it makes no difference. My local bike shop helpful as they are doesnt do electrical issues. Has anyone got ideas please??
Help please? Power comes in pulses
- Thread starter bigsacs
- Start date
Do the pulses coincide with pedal speed. If they do, it's the pedal sensor, and if they don't, it's probably still the sensor.
I had that once when a magnet fell out of the magnet disc. Is yours the external magnet disc type of sensor or the integrated type that slots into the left side bottom bracket?
You also get that problem when the magnet disc gap to the sensor isn't an even 1mm, or when the magnet disc is slipping on the shaft, or when the inner part of the integrated type sensor slips on the shaft.
Thanks for that, i've just been out trying to work out which it might be. Its the external one on the left of the bottom bracket.
If l use a lower gear to allow me to turn the cranks faster without gaining speed the power comes in shorter pulses. Turning them slowly gives longer pulses . The sensor seems to have 7 tiny magnets but with 12 slots and it has Das-kit P12L stamped on it. I couldn't find anything exactly the same on ebay, are they a universal item and would the P12L actually mean its a 12 magnet sensor??
If l use a lower gear to allow me to turn the cranks faster without gaining speed the power comes in shorter pulses. Turning them slowly gives longer pulses . The sensor seems to have 7 tiny magnets but with 12 slots and it has Das-kit P12L stamped on it. I couldn't find anything exactly the same on ebay, are they a universal item and would the P12L actually mean its a 12 magnet sensor??
Are you saying it is the one piece integrated PAS rather then the separate two piece Magnet disc and sensor ?
P12L is indeed a twelve pole PAS .
I googled P12L PAS sensor and got a two piece set up.
P12L is indeed a twelve pole PAS .
I googled P12L PAS sensor and got a two piece set up.
Its a separate two piece Magnet disc and sensor. I used a crank extractor to take off the crank and was able to split both parts of it. It seems in perfect condition with no signs of wear. I've yet to look inside where the wired connection goes to. I might try replacing it with a new one or is it possible to use anything else? thanks
The disc it self needs to fit the axle very tightly , if you are able to rotate it's axis aound the axle by hand then it is the reason you are feeling it pulsing .
So first one needs to check that it can't be rotated around it's axis.
Secondly the disc needs to be very close to the sensor head , the magnets need to pass by the sensor with a 1mm gap and the disc needs to be parallel in it rotation with little or no warping.
Thirdly if the Red LED blinks as the disc passes the sensor head then electrically it should be fine.
The first two points are crucial for it to have a chance of working correctly.
So first one needs to check that it can't be rotated around it's axis.
Secondly the disc needs to be very close to the sensor head , the magnets need to pass by the sensor with a 1mm gap and the disc needs to be parallel in it rotation with little or no warping.
Thirdly if the Red LED blinks as the disc passes the sensor head then electrically it should be fine.
The first two points are crucial for it to have a chance of working correctly.
If on the next ride the PAS is still on/off and not picking up then one will have to look at the magnet disc securing as it will often indicate that the disc is slipping in it's axis around the BB axle. These discs grip the BB axle with small plastic splines which ove r time can lose their grip.
Besides a new disc which will grip better one can try some electrical tape wrapped around the axle or amalgam tape and then fit the disc on to the tape to try and grip better.
Besides a new disc which will grip better one can try some electrical tape wrapped around the axle or amalgam tape and then fit the disc on to the tape to try and grip better.
It's a standard sensor, but DAS KIt are sneaky. They swap the connectors round from male to female, so the standard ones don't fit, so you have to cut the wires and put the opposite connector on one side or the other - prefarably controller side so that you don't have to do it again. They do that so you have to buy spares from them at an inflated price. You should be able to get one from Leoncycle. I think the website is worked from Germany, where they have a UK sales agent:
saneagle, thanks for that. I had a look this morning inside the box under the downtube that the wires go to. Its an awful looking thing full of circuitboards and connections then filled with some kind of resin i presume to give it weatherproofing. i have my doubts wheter i'd be able to get the wires out to solder a new sensor on. I also had the bike upside down and watched the crank sensor/pickup while turning the pedals by hand. It didnt go out of alignment at all and the red led flashed away happily but l could hear the power pulsing on and off, argh! Is there anything else i can try? Is it possible to fit a throttle and just use that ? Albeit it might fall foul of the law!!! Where would a throttle connect into the wiring? So many questions but i'm a bit stuck, thanks.
I didn't mention this before because there seemed to be people on the case who know much more the I do;
but are you sure the sensor didn't originally have 12 magnets and some have gone awol.
The red led would flash away, just not to the right pattern. I doubt anyone could tell the difference by eye. The wrong pattern would cause the odd behaviour.
I did mention magnets falling out above, but according to what he wrote himself, there are 5 missing, which would be the cause of the problem. The problem can be temporarily solved by pressing out anothe one to leave 6 and place them in every other hole to get an even pattern. They must be kept with the same orientation N/S. Use a bit of superglue to make sure they don't fall out. The magnets can be bought from Ebay for next to nothing. My guess is that N35 would probably work better than N52, but I never tested to know which grade are in there, but I do know that the sensor can get swamped by too much magnetism.
Can we see a pic of the magnet disc ?
As said if only 7 magnets press one out and then sort the others out so they are spaced equally.
Alternatvely buy another manet disc .
As said if only 7 magnets press one out and then sort the others out so they are spaced equally.
Alternatvely buy another manet disc .
Thats an interesting idea, Its only from your posts and looking online i've realised P12L means 12 magnets and left hand fitting. i've taken a photo of the magnetic disc and it shows what i presume are 7 magnets?? I've no idea how it relates to being a 12 magnet disc. There are 12 slots do you think its possible there were 12 in the empty slots and somehow they've all come out or have NCM somehow managed to just use 7 to emulate 12??? Thanks again.
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That's the integrated type. We were expecting the open external type because That's what you said in post #3. The type you have can slip on the shaft either when they get worn or when they're not installed properly so the inner rubs on something. Look at the position of the writing in relation to the pedal, then turn the pedal a few rimes to see if it remains in the same relative position. If it doesn't, it's slipping.
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If that PAS sensor set up was working fine previously then one has to look at the fitting on the BB axle which has been alluded to.
As said note the wire entry position on the sensor , rotate the cranks to check it's position does change.
There needs to be a gap between oute sensor face and inner crank face so no fouling/rubbing.
One does suspect there is crank slip with the sensor.
The sensor outer section is usually held firm by the castellations being push firmly to engage with the BB castellations , this prevents the outer from rotating.
Meanwhile the inner section with magnets has to freely rotate when the crank is turned , one has to ensure the inner splines aren't slipping on the BB axle . A wrap of electical tape on a cleaned uncontaminated BB axle and gently push the sensor back over it and engage the inner face in to the BB housing to prevent the sensor outer from rotating may help.
As said note the wire entry position on the sensor , rotate the cranks to check it's position does change.
There needs to be a gap between oute sensor face and inner crank face so no fouling/rubbing.
One does suspect there is crank slip with the sensor.
The sensor outer section is usually held firm by the castellations being push firmly to engage with the BB castellations , this prevents the outer from rotating.
Meanwhile the inner section with magnets has to freely rotate when the crank is turned , one has to ensure the inner splines aren't slipping on the BB axle . A wrap of electical tape on a cleaned uncontaminated BB axle and gently push the sensor back over it and engage the inner face in to the BB housing to prevent the sensor outer from rotating may help.
Nealh, thanks for the suggestions re slipping etc I've had a busy morning trying to understand what the heck is going on. My wife has an almost identical NCM bike so without asking (i'll be in trouble) l swapped just the magnetic disk from hers and hey presto my bike now works perfectly!! I tried putting the suspect part on hers and the problem recurred. I've tried tape on the bottom bracket shaft and using a small blob of paint to mark positions and l now know it doesnt move on the shaft so it appears its just the magnetic disk thats at fault. There's no obvious signs of wear or indeed any difference at all to the one from my wifes bike which incidentally also has just 7 magnets. Its made of just plastic and magnets so i'm now wondering if somehow the magnets have lost sufficient magnetic field to signal the sensor?? Has anyone any suggestions, school boy physics seems to make me think i can re-energise them from a stronger magnet but not sure? Has anyone any suggestions please
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