Re: 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>

Terry & list,

Good idea, but the resistor was within a few percent of the 1500 ohms.
Besides, the same DC current was going through it before and after adding
the 6 mfd reservoir cap between the resistor and the RSG, so I believe it
has to be an inductive effect.
--Steve
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, July 11, 2001 7:31 AM
Subject: Re: Power Resistor - first light!


> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> Hi Steve,
>
> You may want to check the power resistor's resistance with an ohmmeter.
It
> would not be the first time one of these things was miss marked.  Jon had
a
> similar problem and found his resistor was on order of magnitude different
> that the marked resistance.
>
> Cheers,
>
> Terry
>
>
> At 10:56 PM 7/10/2001 -0600, you wrote:
> >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
> >
> >
> >
> >
>
>