high voltage measurement w/ divider

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

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <tesla729-at-cs-dot-com>

Hey all,

I was wanting to build a voltage divider out of some spare 10
meg resistors that I had laying around to safely measure the
charge voltage of my 200 uFD, 10 kV energy discharge cap bank
for my can crusher/quarter shrinker assembly. I was wondering
if I could accurately measure the known fraction of the total
voltage by placing 10 of these resistors in series and measur-
ing 1/10 of the total voltage across just one of the resistors?
I know this principle works because of Ohm's law and all, but
what my real question is would the 100 megs be too much resis-
tance to get an accurate and reliable reading on my Sperry DVM?
I think most DVMs have at least 20 kOhms /volt deflection so
it seems that measuring up to 1000 volts (1/10 of the 10 kV)
should be ok since 20 megs (20 K X 1000 volts) is greater than
the 10 meg for each resistor. BTW, these are the Digikey 10 meg
resistors that many of you are using as bleeders for your MMCs.

Also, I think these are 1/2 watt resistors and if my math is
right, they should be dissapating 1 watt when the caps are
charged to the full 10 kV (10*4 V/10*8 Ohms= 10*-4 amps or
0.1 mA and therefore 10 kV X 0.1 mA = 1 watt. I think this
doubling of their wattage rating on such an intermittent ba-
sis should be ok?

Thanks for any help,
David Rieben