Re: Homemade Voltage Divider

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>

In that case, you could always calibrate your
home-made voltage divider with your HV probe. It
doesn't even matter if you're not linear, or off a
little, as long as you know where 10 kV is.

Adam

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

> 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
>  >
>  >
>  >
>
>
>