Re: HV voltage divider

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Most commercial dividers have a vacuum spark gap (like those in surge
protectors) across the bottom resistor, just in case the big resistor
flashes over.  And, as another poster pointed out, make sure the ground
clip doesn't come off, or your voltmeter floats up to HV. This is one
reason I like measuring the voltage across the resistor, rather than a
series meter... If the thing flashes over, a series meter winding acts like
a fuse (it's really tiny wire), and then the case of the meter floats
up..., or it arcs inside, or..in general "bad things" happen.

Tesla list wrote:
> 
> Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<davep-at-quik-dot-com>
> 
> Tesla list wrote:
> 
> > Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jimlux-at-earthlink-dot-net>
> 
> > Exactly how you'd do it....
> >Is the meter impedance really 10 Meg, or is it 11Meg?...
> 
>         Concur.
>         with one minor comment:
>         Suggest checking the power rating of the high meg resistor.
>         (yes.  The resistance is high, so the currents low, BUT THE
>         Voltages high.  Also look at the sparkover possibilities
>         'along' the multiplier R.  (One such probe i ahd worked the
>         resistor in liquid freon...)  If the high r resistor fails,
>         or sparks over, the voltmeter is toast....
> 
> > You can always calibrate it with a known source...
> 
> > Tesla list wrote:
> 
> > > Original poster: "Richard Williams by way of Terry Fritz
> > <twftesla-at-qwest-dot-net>" <richardwwilliams-at-earthlink-dot-net>
> 
> > > I have a 990meg ohm resistor salvaged from a HV DC probe whose
> >>meter was shot.  Can I add a resistor in series, 10 meg ohm?, to
> >>ground to measure HV? Haven't tried it since I'm leary of inflicting
> >>damage to my digital meter since I've never done this before. Input
> >>impedence of the meter at the 700vac range is 10meg so would that
> >>"look" like a 5 meg resistor overall?
> 
>         best
>         dwp