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Re: Homemade Voltage Divider



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi David,

Your probably going to want to go into Mohm values. Here's a site I found which might answer some questions regarding DVM impedance situations.
http://repairfaq.ece.drexel.edu/sam/hvprobe.htm#shvbas

For maybe an FSD reading of 20kV (10kV center), I would set R1 at 100 Mohm (=19,802V, 0.2mA, 3.9W) and R2 at 1 Mohm (=198V,0.2mA, 0.039W). That would be a simple 100:1 divider (20kV = 200V). Then you just need to figure out what comprises R1 (it will feel the 20kV).

For low risk, get one of those cheap throwaway meters while measuring across R2 (the low voltage side), just to be safe, at least, until you feel comfortable with your divider. Hate to see a nice meter meet Mr. Kilovolt.

Take care,
Bart

Tesla list wrote:

Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Hi all,

I am pondering a way to reliably measure 10 KVDC
across the terminals of (2) 100 µFd energy dis-
charge caps that I plan to build a quarter shrinker/
can crusher project with. I will have up to a total
of 450 µFd at 10 kV when I get 2 other 120
µFd, 10 kV caps added to my collection. Anyway,
I was originally going to just use my Beckman HV
probe in combo with one of my DVMs to monitor
the voltage at the cap terminals to insure that I
do not overvolt the caps, since my HVDC supply
can go up to about 20 kVDC. However, I believe
the HV probe isn't desinged to be used like this
as its ergonomics lends it for hand held operation
so I was thinking of getting some 10K or 100K
carbon resistors and building a 100 resistor di-
vider to get a 100:1 reduction to safely
read 10 kV on my DVM as 100 volts. What
are the best resistance values to go for 10 K
or 100 K? A 1 Meg total with 10K(X100) would
still allow 10 mA of current flow at 10 kV and that
would translate to 100 watts (WOW)! I suppose
that I just answered my own question- don't think
(100) 1/4 resistors would take much of that! Better go
for 100 K per resistor, that would only allow up to 1 mA
of current flow at 10 kV and 10 watts. I believe 10
watts spread over (100) 1/4 watt resistors would work ;^)
Any comments or suggestions?

David Rieben