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I happen to read Bill Mohat’s interesting article, chapter #3 in the new “Outboarder”
today regarding condensers. It was timely as I was also going thru
another magneto from a Scott Atwater 7.5 hp Bail-a-matic.The article suggested if you didn’t know the correct mfd value of your
condenser, you could check your old condensers vial a digital
capacitance meter, which I did on both Scott mags I’ve worked on lately.The specs for these Phelon condensers (FG-471-B) show they should
be in the .12 to .16 range.Today’s condensers checked out at .28 and .31 mfd’s, and the two on the
previous mag with the same condensers, checked out similarly.Mr. Mohat suggested checking the mfd’s on your condensers “before” any
load testing on them, as further breakdown from load testing will effect the
capacitance readings. I don’t believe the article said if the readings will get
higher or lower as the condenser’s deteriorate.What’s been your experience? Do old condensers eventually read higher or lower
on the mfd testing?While working on the previous mag, I tested my meter on new .15 capacitors and they checked
out at .14, so my meter is “close”.The article also suggested from testing, there’s quite a bit of leeway in using
the correct capacitance condenser, and a rating a little “higher” is better
than “lower” than the specs state.
Seeing how I was out of the axial .15 caps, I installed some .2 radial caps on this mag.
I’m guessing it will spark just fine.
Prepare to be boarded!
And at my age, I (ahem) leak pretty badly.
Notwithstanding, I read Mr. Mohat’s article. He did a pretty good job at saying what he was trying to say, and I applaud him for it. Coil/Capacitance (LC) circuits are pretty complicated and magneto ignition circuits are no exception. There are a lot of things happening every time it produces a spark, and it is hard to explain it all in terms understandable to a novice. In fact, I get some more grey hairs every time I think about it. And I have a diploma that says I am a TV repairman (Not). But to share a grey hair, when the magneto points open, electrons flow into the capacitor and the voltage across the capacitor increases with time It is mighty fast, but not instant. When the time is up, the electrons flow back out in the opposite direction in series with the coil. It is that reversal in direction that induces a spark voltage in the secondary winding. A way too big (mfd) capacitor will not charge up to as high a voltage in the time available as would a small capacitor. Also, a leaky capacitor loses energy through the leak just as a leaky bucket takes longer to fill with water.. On top of all that, there is an issue with RPM.
OK, I’ve got everybody confused now, including myself.
KISS is a good thing.
Ok guys what happens when you run the wrong capacitor in your motor? No spark? No performance? Coils get ruined? I see in most of the charts that the .2uF is quite common. Spark is generated the same way by magnetism.
BTY some of us have not received our magazine yet!
dale
As I tried to say, the capacitor charges up in one direction, then discharges in the opposite direction, in series with the coil. Several factors combine to affect the voltage that it charges up to. A higher charge voltage in series with the coil voltage creates a higher reverse current through the coil, which results in a higher AVAILABLE spark voltage. AVAILABLE emphasized because the actual spark voltage only rises till it jumps the plug gap. Then it’s all over till next time. In other words, the actual spark voltage is rarely the maximum it can produce. BUT if it it cannot produce enough to jump the gap reliably, you get no-start, hard start, missing, etc etc.
And of course the pitting issue is another result.
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