Power Resistor - first light!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>" <youngs-at-konnections-dot-net>

Folks,

Here is a strange, unexpected result of current limiting with a power
resistor.  I put a 55 watt 1500 ohm power resistor in series with my 10 KV
DC supply and my SPDT RSG.  Purpose was to limit tank cap charging current
so I wouldn't pop microwave oven diodes in the power supply.

As I was running my twin TC for the first time, I happened to glance down
and noticed the power resistor was glowing red-orange!  Not the sort of
first light I wanted!  But the current was only about 45 ma through it.  The
power dissapation should have only been 3 watts, but it must have been at
least 100 watts to make it red-orange hot!

So, what's going on?  Has to be that the inductance of the wire wound
resistor was making it act like a much higher impedance to the high current
pulses going through it.

Putting a 6 mfd cap across the feed to the RSG & tank circuit stopped the
pretty glow - power resistor was cool to the touch as it was now just having
a fairly constant 45 ma flow through it.

Moral of the story - wire wound power resistors are also inductors, and can
cause weird, unexpected effects.

--Steve