High voltage,high resistance film resistors are still made the same way,
with a spiral element to maximize the element's lenght.
73
Bill wa4lav
At 06:24 AM 4/28/2005 -0400, Will Matney wrote:
>See below;
>
>*********** REPLY SEPARATOR ***********
>
>On 4/27/05 at 2:26 PM Bill Fuqua wrote:
>
> >Believe or not Resistors have a voltage limit and rating. The standard 2
> >watt carbon film resistor is only rated for 300 or 400 volts DC. They can
> >be pushed higher but not by a lot. The same is true for Carbon Comp.
> >resistors. If you put several thousand volts across a standard carbon film
> >or comp resistor you may get some exciting fireworks even thought you have
> >not exceeded their power ratings. A series string is the best choice for
> >high voltage applications.
>
>It's the same method used to determine the breakdown voltage in the
>windings of a transformer. As, there's so many volts per layer of winding.
>The difference between any two layers in volts is what the thickness of
>the fish paper is determined by, and not by how many total volts the whole
>winding is.
>
>They do make special high voltage resistors.
> >They are much longer than ordinary resistors. We have some carbon comp HV
> >resistors that are almost a foot long.
>
>I remember the old focus resistors in TV's. You could see that spiral
>where they put on the resistant coating down its length. Kind of reminds
>you of a barber pole. They looked to me like they just covered them with a
>varnish or something. They were about three inches long or so, and the
>turns had a decent air gap between each. I think the air gap on any
>resistor is what determines its voltage rating. The only type that
>wouldn't apply to would be a carbon comp as the just had a slug of
>resistance material with leads attached to each end.
>
> >
> >73
> >Bill wa4lav
> >
> >
> >At 11:11 AM 4/27/2005 -0700, aborg wrote:
> >>What about using 10 2 Meg 2 Watt resistors in
> >>parallel ? The math indicates it should work.
> >>****************************************************
> >>--- Phil Clements <philc@texascellnet.com> wrote:
> >> > Your bleeder is too small. All you need a bleeder
> >> > for on a C input filter
> >> > P.S. is to drain the HV after shut-down. Your
> >> > 100,000 ohm resistor is
> >> > flowing 160 ma of current, and just heating itself,
> >> > your components, and
> >> > your ham shack. I would use at least 200 k to 400k
> >> > ohms. In all my 4 kv+
> >> > power supplies here, I use 4 X 100k ohm @ 100 watt
> >> > units in series. (225
> >> > watt units will be better) Even these get really
> >> > warm, but do the job just
> >> > fine. I always double the wattage on the bleeder
> >> > resistors as a safety
> >> > factor. You don't want one of these babies to go
> >> > open on you!
> >> >
> >> > (((73)))
> >> > Phil Clements, K5PC
> >> >
> >> >
> >> > -----Original Message-----
> >> > From: amps-bounces@contesting.com
> >> > [mailto:amps-bounces@contesting.com] On
> >> > Behalf Of aborg
> >> > Sent: Sunday, April 24, 2005 7:44 AM
> >> > To: Amps Amps
> >> > Subject: [Amps] Bleeder Resistor Inquiry
> >> >
> >> > I am currenty building a HV Power Supply using a
> >> > 4800vac pole pig, 40uF 5kv oil filled cap , 10kv PIV
> >> > rectifier board, 20 amp variac and a 100k 225watt
> >> > bleeder.
> >> >
> >> > The initial power up started well without the
> >> > bleeder
> >> > connected to the circuit after 30 min burn-in no
> >> > problems. Discharged the circuit and added the 100k
> >> > bleeder and 5 mins the bleeder starts to smell and
> >> > the
> >> > exterior paint starts to bubble. Shut it down and
> >> > examined the circuit, all seem accurate.
> >> >
> >> > Question : Is my bleeder to small ?
> >> >
> >> > P.S. : The variac was set at 4KV at all times.
> >> >
> >> > Mike-KK4MS
> >> > a_borg@yahoo.com
> >> >
> >> > __________________________________________________
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> >> > protection around
> >> > http://mail.yahoo.com
> >> > _______________________________________________
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> >> >
> >> >
> >> >
> >>
> >>Mike-KK4MS
> >>a_borg@yahoo.com
> >>
> >>
> >>
> >>__________________________________
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>
>Best,
>
>Will
>
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