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At an idle of about 600 RPM, what AC voltage should the mag post be putting out?

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Around 7-9 volts as I recall. There used to be a graph showing mag output as various speeds but I can't find it now. It may have been on my old crashed PC.

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Thank you, Ken.

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Bill:

While typically good magneto will put out what Ken posted - if you are having ignition problems at higher RPM be advised that a good magneto will also very easily put out over 20 volts when you speed up the motor. A few weak magnetos I have seen will put out correct low RPM voltage but then the position of the crankshaft shifts as the engine speeds up the the magneto never develops the higher AC voltage needed at the higher RPM's. Those will tend to indeed increase AC voltage with higher RPM but will just not be able to get that voltage over 20 volts. That can be problematic for higher speed driving.

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Thank you, John. Bailey and I'll check that out this weekend.

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Here's the Ford factory specs. With a recent recharge you can usually improve on these figures.

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Thank you, Royce. Bailey and I will check this out over the weekend.

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The above numbers are the only numbers ever offered by Ford and they are not specs they are only some measured amounts on a "typical" magneto according to Ford. You will see these numbers copied verbatim by Dykes and others. The way you can know they are "copied" from Ford is that the above numbers contain a glaring error. Since the magnets generate the AC signal coming from the magneto and they are fastened to the flywheel then doubling the RPM has to also double the frequency (cycles). 200 to 400 the cycles exactly double. 600 to 1200 the cycles exactly double but notice that when going from 400 to 800 the cycles do not double leaving the data then questionable. If the magneto has no load on it then the voltage would also double when the RPM doubles. That mistake in cycles is repeated by all postings of these numbers in Dykes and other places leading to the logical conclusion that all numbers came from this same source.

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Lets just look on the RPMs and Cycles. 200 RPMs are 3 1/3 RPS(econd). We have 16 magnets ordered in a NN - SS - NN order making 8 full cycles per revolution. On my calculator it gives 26,7 Cycles.

The 600 RPM are actually right - it gives a 80 Hz and hence 1200 RPNs are also correct. All the other are wrong. 1000 RPMs are just 133,33 Hz.

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Michael:

Yes it clearly shows they were using some sort of estimate for the RPM/Cycles and then measuring the voltage with a Voltmeter probably as accurate as any at that time. The data is not miles off so I am not suggesting it is useless but just that when comparing published data from that era it is important to note that only one set of data seems to have been taken and was used by everyone else. Thus I would take these data as a guideline rather than a spec.

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I know that chart. That's not the one I was thinking of though. I seem to recall a GRAPH. The data was captured with a scope. Perhaps it was an analysis from a HCCT or an early ignition conversion. I just don't remember. Maybe the E-Timer or similar?

I wish the memory chips weren't going bad.