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Re: Homemade Voltage Divider

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 07:46 AM 2/1/2006, you 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.





 <snip>





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?
Actually, having a series resistor also provides a convenient way to discharge the cap quietly and in a safe manner. 

Here's what I do:

AC Line:
 normally open contactor:
 HV Transformer: bridge:
 Normally Closed HV relay in shunt:
 Series resistor
 Capacitor
I have it wired so that you apply power to open the shorting shunt, and, when that relay is OPEN, it triggers a microswitch, which then allows you to apply power to the HV transformer with a momentary contact type latching circuit. 

Here's the advantages:
If power fails, the cap discharges through the series resistor and the NC shunt
If a diode fails, the cap discharges through the series resistor, so the BANG isn't as loud. The momentary contact latch circuit for applying power to the HV transformer means that there are TWO discrete steps enforced: remove shunt, apply power. (If you just wire up a toggle switch to the HV transformer line side, applying power to the shunt relay instantly applies power to the HV transformer, which may not be a good idea.