nuckolls.bob(at)aeroelect
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 Posted: Tue Dec 13, 2011 10:14 am Post subject: No Title |
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At 10:55 AM 12/13/2011, you wrote:
| Quote: | I wired my starter switch and magnetos like Z-26 with the magneto wire shields both connected to the ground terminal on the switch and the other end of the shields connected to motor ground. Before installing the switch I confirmed continuity was correct in all switch positions. Why would one have continuity to ground from the magneto post even when the switch is in the "both" position. In fact there is strangely continuity from magneto post to magneto post. If it matters, the magnetos are Bendix and both have impulse couplings (no jumper required on the switch). I assumed that the magneto post is isolated from ground unless its wired to ground. Is that incorrect?
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No it is quite correct. What your ohmmeter perceives
as "grounded" is really a measurement of the VERY LOW
resistance of a magneto's primary coil (less than 1
ohm as I recall).
The difference in measured resistance for a magneto's
p-terminal to ground with points open verus points closed
is very hard to detect with a garden variety ohmmeter.
This is why one needs a "buzz box" to time a magneto.
The "buzz box" is responsive to changes in AC impedance
as opposed to DC resistance of the magneto p-lead circuit.
Here's a compendium of documents that speak to magneto
timing tools
http://www.aeroelectric.com/articles/Magneto_Timing/
and even a couple of DIY buzz-boxes . . . one by
the inestimable Jim Wier.
Bob . . . [quote][b]
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