"Damian Menscher" wrote in message
...

After reading specs on a 6kV Fluke HV probe, I realize they're really
just voltage dividers (the Fluke uses a 75MOhm resistor and a 75kOhm
resistor). So I figure I could save myself $75 by building my own.
Off I go to radioshack.com, where I find 5-packs of 1MOhm, 1/2W
resistors for $1. Recalling high school physics, I work out that one
of these should be able to drop 707V at .707mA. So if I put 10 in
series, I should be able to measure up to 7kV, and simply measure off
the last one and multiply the voltmeter reading by 10.

In high voltage circuits like that there's not a whole lot
current, and 10 Meg could be a significant load on it;
however, that's probably no big deal.

One problem: Rat Shack says these have a "max working voltage" of
350V (see http://www.radioshack.com/search.asp?find=271-1134). Are
they just arbitrarily throwing a fudge factor of 2 away, or are they
mislabeling 1/4W resistors as 1/2W resistors, or what? (They list
10Ohm 1/2W resistors as 350V max also, so I'm guessing this is safe
to ignore.)

Not exactly. With voltages in that range theres's a possibility
of a flash-over. You definitely want to make the divider so
the resistors are phisically arranged in a series like:
--####---####---####---
and don't use your HV probe when the humidity is too high.

Also, I think those high value resistors are composite, so put
one or two metal films in there -- if something bad happens,
the metal film will evaporate, so in essence, it will act as a
fuse.

If you ever get hit by a CRT, 2.2kV isn't that high of a voltage,
but it can be very inconvenient, or deadly if the PS can supply
enough juice.