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Re: Homemade Voltage Divider

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hi Dave,

Having built my own quarter shrinker and power supply, i will tell you
about what i did.

For measurement i used a resistive divider.  Most meters have a 10M
impedance as standard.  Make a 1:100 divider with the 10meg being the
"1" and the 1G being the "100" (really its 1G-10Meg, but this is close
enough).  This should get you within a few % tolerance.  I used real
HV resistors on my divider, but you could series up many LV resistors
just as well.  I then use my DMM (cheap $12 one) to read the voltage
at the divider.

For charging i have a constant current source (HV SMPS i built), but
just in case, i also have a 3k limiting resistor.  Your 3k 250W
resistor sounds just fine.

Overbuild the diodes on the supply, say 2-3X the voltage they will
really see.  You dont want them failing in this situation!!  The 3k
resistor will limit the current to something reasonable if they do
fail.  Also, have a HV disconnect relay between the charging supply
and the cap.  Disconnect the HV supply before discharging the cap!!!

My setup works flawlessly so far.  You can see some older pics of it
on my website at:




On 2/1/06, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
> Dr, all,
> Yes, this is true, but when you're measuring the
> voltage of a charging capacitor bank at the
> capacitors' terminals while charging the caps
> up, the measured voltage will be considerably
> lower than the applied voltage until the caps'
> charge voltage reaches equalibrium with the
> charging supply voltage. This is due to the
> heavy load that the caps place upon the power
> supply while charging and also the reason that
> the power supply's voltage must reach higher than
> the desired charge voltage of the caps. Otherwise
> it would take an excessive period of time to fully
> charge the caps if the maximum available supply
> voltage was only about equal to the max charge
> voltage of the caps. Since the power supply's
> voltage must reach higher than the caps' rated
> voltage, the measured DC voltage at the capacitors'
> terminals must be measured and the power supply
> immediately shut off when the voltage at the caps'
> terminals reaches their rated voltage to prevent over-
> volting of the caps, thus my reason for measuring the
> DC voltage at the caps' terminals.
> Also, I was wanting to know if I would need some
> type of HV resistor in series with the HV DC input
> to the caps since the bombarder transformer supply
> isn't current limited? I would gradually ramp up the
> voltage input to the bombarder with a variac while
> monitoring the voltage at the caps' terminals but the
> bombarder can act almost like a dead short while
> charging >400 µFd of capacitor towards 10 kV
> until the capacitors' charge gets close to the applied
> voltage. I have a ~250 watt, 3 kOhm resistor that I
> could use. Would this be about the right size and
> resistance for this purpose?
> Thanks,
> David Rieben
> ----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Tuesday, January 31, 2006 10:35 PM
> Subject: Re: Homemade Voltage Divider
> Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
> You never need to measure the DC voltage.  It's
> always 1.414 x the Erms, so you are actually
> measuring Erms and then just recalibrating the
> meter face to reflect the actual measured DC
> potential.  No messing around with HV resistors, etc.
> Dr. Resonance
> When I mentioned the NST method I was thinking he
> wanted to measure the AC input to the DC filter -
> didn't engage brain. Transformers don't work well at DC.
> Jim
> ----- Original Message -----
> From: <mailto:tesla@xxxxxxxxxx>Tesla list
> To: <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx
> Sent: Saturday, January 28, 2006 12:00 PM
> Subject: Re: Homemade Voltage Divider
> Original poster: Yurtle Turtle <<mailto:yurtle_t@xxxxxxxxx>yurtle_t@xxxxxxxxx>
> An NST will work for AC, but not DC.
> Adam
> --- Tesla list <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx> wrote:
>  > Original poster: "James Zimmerschied"
>  > <<mailto:zimtesla@xxxxxxx>zimtesla@xxxxxxx>
>  >
>  > I am pondering a way to reliably measure 10 KVDC
>  > across the terminals of (2) 100 µFd energy dis-
>  > charge caps Original poster: "David Rieben"
>  >
>  > David
>  > Richard Hull showed the use of a NST is reverse
>  > to measure high voltages. This might be bulky but
>  > reliable.
>  > Jim Zimmerschied
>  >
>  >
>  >