RE: TC Part alternates

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Michael,

At 12:33 PM 12/19/2002 -0800, you wrote:
>Since I obviously don't have a modicum of understanding of electrical
>theory, can you tell me the voltage rating requirement for the bleeder
>resistors?  I, being limited in my understanding, would think you would need
>resistors that can handle 2000v.

Yes, the resistors have to be able to easily handle the full voltage across 
the capacitor.


>However on this board I see experienced
>people recommending 1/2 watt carbon film resistors that have about 350v max
>working voltage.

That's me :o)  See this post:

http://www.pupman-dot-com/listarchives/2000/November/msg00073.html

The resistors don't arc over the outside even at wild voltages.  Heating 
seems to be the problem but they seem rock stable to 1600 volts dc which is 
like 2200 volts AC.  People that use them (there are tens of thousands out 
there...) seem to have very few problems (be SURE to space the resistors 
away from the cap bodies!).  So even though these resistors are technically 
far under rated for 2000+ volts, they seem to work fine.  They cost about 
one penny each and I send them to people for free ;-)  If people are 
worried about the voltage, I just tell them to use two in series...

The resistors are from DigiKey.  # 10MH-ND.

www.digikey-dot-com


>Others say no you need a 2000v resistor and they recommend metal glaze
>resistors.

Those are "real" high voltage resistors and they work great.  They just 
cost a lot of money.  However, some people have found really good prices on 
them.  They work perfectly fine too.


>In my searching the metal glaze resistors have a higher voltage but nothing
>near 2000v.  I have found thick film resistors that will handle 2000v but
>they are rather pricey.

Yep...

BTW - 1/4 watt resistors will NOT work (too small).  I imagine 1 watt and 
higher will work fine too.  I just got started using the 1/2 watt types 
because I had them laying around in the early MMC days and stuck them 
on...  I guess the rest is history :o))

Cheers,

         Terry



>Thanks for your help.  I learn more each day.
>
>
>
> > -----Original Message-----
> > From: Tesla list [mailto:tesla-at-pupman-dot-com]
> > Sent: Thursday, December 19, 2002 7:44 AM
> > To: tesla-at-pupman-dot-com
> > Subject: Re: TC Part alternates
> >
> >
> > Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <Mddeming-at-aol-dot-com>
> >
> > In a message dated 12/18/02 7:09:49 PM Eastern Standard Time,
> > tesla-at-pupman-dot-com writes:
> >
> >
> > >Allelectronics has the caps but the closest resistor I could
> > find there is:
> > >400 ohm/50 watt ceramic
> > >I could put 3 in an series to get 1200 ohms but what happens to
> > the watts?
> >
> >
> > Your composite resistor will be able to dissipate 150 Watts.
> >
> > >I also read I should use 10M ohm 1/4 watt 2000 volt bleed
> > resistors for the
> > >Geek Group caps, but isn't the 1/4 watt a problem?
> > >Isn't there a lot more than 1/4 of a watt going through them?
> >
> >         The power supplied TO the SYSTEM is not the power being
> > dissipated
> > (used up) BY each RESISTOR. The power being dissipated by the resistor is
> > E^2/R, where R is the resistance and E is the voltage drop across each
> > resistor.For say, 2000V drop across each cap, a pair of these in series
> > would each dissipate 1000^2/ (10^7 )=0.1 watts. Now 2000v across a single
> > 10M resistor  would dissipate 0.4 watts, in which case a 1/2 watt
> > resistor
> > would be a better choice.
> >         This points out why some modicum of understanding of electrical
> > theory is preferred before completing a coil.
> >
> > Matt D.
> >
> >
> >