Hi Jon
I think I saw your pickup at the Aldworth meeting it could not be said to be well made. For the benefit of others struggling to get the NLM pickup to work could you say how many camshaft degrees (advance or retard) you had to change the rotor by? With the standard ignition it is easy to electrically retard the ignition this might work with the NLM pickup but that is that what was needed or did you need to advance more.
Mark
No sparks.
Re: No sparks.
Hello Mark
Yes, you did see the NLM pickup at Aldworth. I needed more advance on the rotor to get the timing right. I determined the additional advance required empirically. I set the pickup at max advance and using a strobe estimated the shortfall. With the engine stopped I set the flywheel at PMS1 and looked at the gap between the rotor and the pickup coil. Then estimated the difference in rotor position to get it in the adjustment range. This wasn't critical because there is quite a lot of adjustment on the pickup. Just needed to make sure the new rotor would get in range. Not very scientific but it worked. I looked at the rotors and I would estimate the the new rotor is about 5 degrees more advanced than the one supplied.
I found it difficult to make changes to the timing because very time I moved the back plate the rotor / coil air gap changed as well so then had to reset the air gaps. If the back plate had been thicker that may have helped as I think it distorts when the screws are tightened.
The NLM pickup was sold as a universal one for all types of transducers. I tried a diode in the line from the pickup to the transducer to replicate the the later type transducers and that made the lack of advance worse, as I expected. Discussion of what is going on electrically and magnetically is probably best done over a beer!
Yes, you did see the NLM pickup at Aldworth. I needed more advance on the rotor to get the timing right. I determined the additional advance required empirically. I set the pickup at max advance and using a strobe estimated the shortfall. With the engine stopped I set the flywheel at PMS1 and looked at the gap between the rotor and the pickup coil. Then estimated the difference in rotor position to get it in the adjustment range. This wasn't critical because there is quite a lot of adjustment on the pickup. Just needed to make sure the new rotor would get in range. Not very scientific but it worked. I looked at the rotors and I would estimate the the new rotor is about 5 degrees more advanced than the one supplied.
I found it difficult to make changes to the timing because very time I moved the back plate the rotor / coil air gap changed as well so then had to reset the air gaps. If the back plate had been thicker that may have helped as I think it distorts when the screws are tightened.
The NLM pickup was sold as a universal one for all types of transducers. I tried a diode in the line from the pickup to the transducer to replicate the the later type transducers and that made the lack of advance worse, as I expected. Discussion of what is going on electrically and magnetically is probably best done over a beer!
Re: No sparks.
Found much the same on mine - a lack of advance and did a similar calculation (guess!) on the amount of slot opening required. It is fiddly moving the timing a little at a time when there is no eccentric or vernier type adjustment screw and also having also to reset the air gap as it invariably moves a little - which is more than enough. Once set it seems to stay set fortunately but I'm sure a better engineered solution could have been made initially. Maybe now with improved (and lower cost) CNC and electronic systems it could be improved upon.
One day maybe Stuart or others involved may be able to fill the development gaps.....
One day maybe Stuart or others involved may be able to fill the development gaps.....
robint
(Morini, Enfield, Deauville, SLK and home to support)
(Morini, Enfield, Deauville, SLK and home to support)
Re: No sparks.
Thanks guys
To summarise.
When using variable reluctance sensor NLM pickup.
1. The running clearance (not air gap) should be set as small as possible and certainly much less than 0.1mm.
2. If full advance cannot be achieved the either the slots need to be lengthened or a new rotor made.
3. An iterative process of checking advance and running clearance is required as adjusting advance can cause change in clearance.
4. Advance must be confirmed on both cylinders and appropriate (ANT2) mark will be required for some generator rotors.
Please correct if my understand is in error.
Mark
To summarise.
When using variable reluctance sensor NLM pickup.
1. The running clearance (not air gap) should be set as small as possible and certainly much less than 0.1mm.
2. If full advance cannot be achieved the either the slots need to be lengthened or a new rotor made.
3. An iterative process of checking advance and running clearance is required as adjusting advance can cause change in clearance.
4. Advance must be confirmed on both cylinders and appropriate (ANT2) mark will be required for some generator rotors.
Please correct if my understand is in error.
Mark
Re: No sparks.
My understanding from perusing datasheets is that conventionally the VR interface circuits use the positive zero crossing which would imply negative then positive waveform. In our case we use the positive pulse with a trigger of around 0.75V. I don't know if the sensor is arranged to produce negative then positive
or vice - versa. If the former then reversing it's connections will advance the trigger. just a thought.
A quick look with an oscilloscope would confirm.
Also there is no need for a diode as the sensor will only produce one positive pulse as the rotor passes.The negative pulse has no effect on the thyristor in the transducer so long as it isn't so large as to cause device breakdown by exceeding the negative gate breakdown voltage which seems unlikely.
Adding a diode will simply retard the ignition and as found by Jon not help.
Mark
or vice - versa. If the former then reversing it's connections will advance the trigger. just a thought.
A quick look with an oscilloscope would confirm.
Also there is no need for a diode as the sensor will only produce one positive pulse as the rotor passes.The negative pulse has no effect on the thyristor in the transducer so long as it isn't so large as to cause device breakdown by exceeding the negative gate breakdown voltage which seems unlikely.
Adding a diode will simply retard the ignition and as found by Jon not help.
Mark