| Pertronix install on Onan mysteries [message #278782] |
Sun, 31 May 2015 12:53  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
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Senior Member |
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Ok, first off, Murphy's law follows me everywhere so no doubt most others have not have this problem.
First, even before the epoxy had even cured, I discovered that I installed the magnet with the wrong side towards the Pertronix sensor. Then, since the markings were gone from the magnet, I did it again! Then I got smart, I used a compass to find the South Pole of the magnet. I got the space gap set to 0.025" but it would not start, just the odd firing (this could be when I let off the Start button and the coil collapsed causing a spark at any point in the cycle).
So I disconnected the Pertronix and reconnected the points and it starts right up, so not a fuel issue.
Just to see what is happening, I connected a 12V LED string in place of the coil on the Pertronix. Slowly turning the flywheel with the magnet under the sensor, the LEDs would go off (Coil field would collapse and spark occur) but the OFF time was very short, like 1/2 the top width of the ring gear tooth. Doing some calculating, the OFF time to the coil is less than 1 degree, meaning at 1800rpm, the time for the coil to collapse is about 0.1ms. I believe that's hardly long enough...?
So I removed the Pertronix module and move it over the magnet across different areas of the sensor. Turns out on mine, centering the magnet's pass directly under the yellow dot (where I carefully installed it to be) is about the least sensitive spot. If I move it to pass under the edge opposite from its mounting point, I'll be able to extend the off time to about 1/4" across the Pertronix's face. Ok, I'll try that but I need to wait till tomorrow to try again as the epoxy needs to cure again!
So, that 1/4" of travel across the face = ~2.3degrees of rotation and will last 0.2ms. I still think that is too short for the coil field to collapse.
Another concern I have is the coil duty cycle. On the old points system, the points are open until a few degrees before spark is desired, then they close and the field builds up in the coil. The points then open, the coil field collapses and spark occurs igniting the cylinder mixture. The points then stay open until just before the next firing and repeats.
My observation of the Pertronix is coil current is supplied the entire time until the magnet crosses the face of the Pertronix sensor. In my case 360-2.3 = 357.7 degrees of rotation or 99.4% of the time. In the case of my coil, that's about 45watts of power.
In a normal Pertronix installation there are 4-8 magnets on a disk that is a couple inches in diameter, running at 1/2 engine speed meaning each of the many magnets are moving much more slowly across the Pertronix sensor. To match the points system, we would actually need to run a strip magnet around the circumference of the flywheel. Or invert the output and use a magnet a couple inches long.
Has anyone noticed failures of the Onan coils after the Pertronix installation?
What is the ideal OFF time for a coil to collapse and fully fire a spark plug?
I know I reading too much into this.
thanks guys.. and thanks to Gary Bovee for his excellent kit and his help.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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