Re: Wire-wound resistors as dummy test load

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

Original poster: "sundog by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sundog-at-timeship-dot-net>

Hi All,

  A note on wire-wound, aluminum cased power resistors...

  I used some 3kohm, 25w power resistors an the grid-leak resistors in my 
old dual 833A VTTC.  After about 1 minute of operation, the endcap blew out 
explosively (ceramic shrapnel went everywhere), shooting across the garage 
and shattering against the far wall.  The resistor itself was attached to 
the coil's deck with small wood screws, so it stayed in place.

   Be wary of these resistors.  They don't seem to like having their 
wattage rating exceeded, and complain very loudly by blowing and throwing 
out shrapnel. I think I'll stick to ceramic core wirewound resistors from 
now on :)

At 10:09 AM 10/3/02, you wrote:
>Original poster: "Richard W. by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><potluck-at-xmission-dot-com>
>
>List,
>
>Got it. :) This is interesting.
>I have 43 50 watt 50K Dale aluminum power resistors. 2 chains of 20 could
>theoritically handle 15Kv -at- 30ma for load testing. That calculates to 750
>volts at 30ma disspating 22.5 watts each.
>
>I'm a bit leary of trying it though.
>
>The following is vague but...
>I don't believe these are good for HV apllications. And I think they're
>rated for 600v anyway. I've heard the end caps can blow off.
>
>Rick W.
>
>
>
>
>
>----- Original Message -----
>From: Tesla list <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Wednesday, October 02, 2002 7:00 PM
>Subject: Re: Wire-wound resistors as dummy test load
>
>
> > Original poster: "Peter Komen by way of Terry Fritz <twftesla-at-qwest-dot-net>"
><pkomen-at-zianet-dot-com>
> >
> > Ed,
> >
> > Well, let's look at this.
> > 200 Ohm 200 watt resister to dissipate 200 Watts will need a current
>through
> > it of 1 Amp.  Hook 4 in series and run a current of 1 Amp through them,
>and
> > the dissipation for each resister is still I^2 * R or 200 Watts.  The
>total
> > dissipation is 800 watts for the 4 in series.  Figure it 2 ways 4 * 200
> > Watts = 800 Watts or 1 Amp^2 * 800 Ohms = 800 Watts.
> >
> > If the resisters are different resistances are the power dissipated in
>each
> > will not be equal, but if certain things are known about the circuit, the
> > power dissipated in each resister can be calculated.  Suppose that we have
> > two resisters in series: a 1-Ohm 2-Watt resister and a 200-Ohm 200-Watt
> > resister.  If 201V is applied across the two resisters, 1 Amp will flow
>and
> > the resisters will dissipate 201 Watts; 1 Watt in  the 1-Ohm resister and
> > 200 Watts in the 200 Watt resister..
> >
> > Could explain your reasoning?
> >
> > Regards,
> >
> > Pete Komen
> >
> > > Original poster: "Edward Wingate by way of Terry Fritz
> > <twftesla-at-qwest-dot-net>" <ewing7-at-rochester.rr-dot-com>
> > >
> > > Tesla list wrote:
> > > >
> > > > Original poster: "David Speck by way of Terry Fritz
> > <twftesla-at-qwest-dot-net>"
> > > <dave-at-davidspeckmd-dot-org>
> > > >
> > > > Rick,
> > > > Sorry, nope, but in series, each resistor will still be able to
> > > > dissipate its own 200 watts, quite independently of the other three,
>so
> > > > four in series will give an 800 ohm, 800 watt resistor, with maximum
> > > > dissipation when you put 800 Volts at one amp through the string.  A
> > > > single resistor would dissipate 200 watts when carrying 200 volts at
>one
> > > > amp.
> > > > Dave
> > >
> > > Hi Dave,
> > >
> > > The wattage rating of resistors in series is only as high as the
> > > weakest link which in this case is 200 watts. Each resistor is still
> > > being asked to pass an 800 watt total load no matter what each is
> > > dissipating separately and it won't work for long. If you splice 4
> > > pieces of wire together in series they still will only handle what a
> > > single length is rated for in amperes. In parallel the 200 watt
> > > resistors could handle 800 watts because each resistor handles 25% of
> > > the load.
> > >
> > > Ed
> > >
> > >
> > >
> > >
> >
> >
> >
> >

-----------------------------------------------------------------------
Shad (Sundog)
G-5 #1203
"Ever stop to think, and forget to start again?"
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