Re: Homemade Voltage Divider

["Tesla list" <tesla@xxxxxxxxxx>]

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

Hi Adam,

Yes, I forgot that you also have some huge "quarter shrinking"
caps yourself, so your applications of measurement would be relavent
to my situation. Actually, I'm using a 240 volt to 30 kV bom-
barder transformer that's only being fed up to 140 volts in
through a 120/140 volt variac. This allows for up to 15 to
17 kVAC output and I've constructed a FWB rectifier from
HV diodes from an x-ray transformer to make it a 20 kVDC
power supply for cap charging. I've measured the full HVDC
output from it with the variac maxed out and with a 50 kV,
.025 µFd Maxwell across the HVDC output to filter it for measure-
ment and got a 20 kV reading with my Beckman probe. Since
the bombarder isn't current limited, I'll have to increase the
voltage to charge the huge caps throught the variac slowly
to insure that I don't short circuit the mains while charging,
since I'm not using any ballasting in sereis with the bombar-
der's input. Of course, reliable measurement of the terminal volt-
age of the capacitor bank is crucial to insure that I don't
overvolt the monsterous 440 to 450 uFd of caps at >10kV!
I'm sure that internal dielectric flashover failure could result in
disastorous external case rupture! I suppose that I could
just take the Beckman probe apart and hardwire it to the
shrinking circuit as you've done, but that would render my
Beckman probe unusable for making any other HV measure-
ments outside of the shrinker circuit. That's reason I'm consi-
dering building the "homemade" voltage divider.

David Rieben


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, January 24, 2006 9:22 AM
Subject: Re: Homemade Voltage Divider


Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>

What kind of PSU do you have? I have this one:

http://hot-streamer.com/adam/garage/psu_34kV_1.jpg
http://hot-streamer.com/adam/garage/psu_34kV_2.jpg

and built this controller from an old VTVM:

http://hot-streamer.com/adam/garage/psu_34kV_3.jpg

My PSU outputs a voltage, 0 - 5 volts I believe,
relative to output. For calibration, I used a Maxwell
30nf 35kV cap and cranked it up until I hit my target,
which was 10 kV. I simply used the VTVM gauge and a
pot to fine tune it to match my DMM and HV probe.
Although I have used it as a handheld, my HV probe
cane with a removance tip, allowing me to hardwire it
to the circuit I'm measuring. I disconnect my PSU from
the shrinking circuit before firing it.

Adam

--- Tesla list <tesla@xxxxxxxxxx> 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
>
>
>