[SEL] Re: Buzz Coil Tester (for Dave)

[Rob Skinner]

> I got across a buzz coil about two years ago and it really 
> has a bite.  I would guess around 5KV but that's strictly 
> a guess, it would be interesting to know what it really is. 
> Your picture tube tester ought to work fine, I think they 
> are around 20KV.

Hi Jim,
My experiments were on older points/distrubutor type automobiles, but the basics
will be the same.  Actual numbers may differ.

If you take your measurements in situ, you won't be reading the maximum
potential output of the coil.  As the coil fires, but before the spark occurs,
the voltage rises sharply.  Eventually the voltage rises to the point where the
spark jumps between the electrodes.  Beginning at this time, the voltage remains
approximately contant.  Flat line.  About 8kv.  In a low compression engine and
a narrow sparkplug gap, your estimate of 5kv wouldn't be too far out of line.   

If you widen the plug gap, you'll read an increase in voltage, even though the
coil itself has not changed.  If you remove the high tension lead from the
sparkplug and let it hang there, you'll see the voltage skyrocket.  In an older
car, you'd expect to see about 18kv-25kv.  I've got no idea what you'd read on a
buzzcoil, but considering the long spark they'll throw, I wouldn't be surprised
if the voltage is considerably higher.  

Incidentally, it's not really a keen idea to pull the lead off the plug and then
fire the magneto.  The high voltage can destroy the old insulation in an
original coil.  

Rob

=-=-=-=-=-=
Rob Skinner
La Habra, California
mailto:rskinner at rustyiron.com
http://www.rustyiron.com