Thread: Voltage Multiplier

What should the capacitance of the capacitors be in a voltage multiplier? Does it matter?

Does each stage only have to handle the input voltage? Wiki seemed to indicate that, but I have to be sure so I do not blow it up and likely die as a result.

Originally Posted by Cold Fusion

What should the capacitance of the capacitors be in a voltage multiplier? Does it matter?

Does each stage only have to handle the input voltage? Wiki seemed to indicate that, but I have to be sure so I do not blow it up and likely die as a result.

Yes and no. Ideally each component should withstand the total voltage. If only to make it more indestructible while testing and experimenting. But you can use low voltage diodes and capacitors.

The board can jump though. To you, or other objects near it once the voltage gets high.

Things like magnetic fields, radio, or high frequency arcing can cause new arcs to jump between components. Never experiment in strong magnetic fields. Near induction motors or large spools of wire.

As long as you have the amperage in your AC transformer you can use bigger capacitors. However I believe even larger capacitors will eventually charge.

Sincerely,


William McCormick

Cold Fusion

"What should the capacitance of the capacitors be in a voltage multiplier? Does it matter?"

I assume you have each capacitor connected in series from the input (as a chain) and the output (also as a chain). The DC voltages will therefore be divided between each - so say its *8 then the total withstanding voltage is 8 times that of each capacitor.

This is not the only configuration though as each input capacitor can be "feed" from the input to each dual diode connection. In this case the top capacitor sees the full output voltage.

Why do this? In the series configuration the total capacitance reduces towards the top to the multiplier chain (drawn conventionally) as the input capacitors are in series. However each section must supply the same output current so the net impedance of the top section is higher than the lower sections so it becomes a "weak link". Each capacitor holds charge so it needs to be sufficiently large in capacitance otherwise the output voltage will droop when current is drawn.

q = C * V
i = (d q / dt)

Consequently, low AC frequencies need large capacitance values "C" otherwise the voltage across them will fall over the period of the waveform depending on the current flowing "i".

So, in summary the two configurations trade off voltage handling capability per capacitor versus total (series) capacitance up the multiplier chain.

Note: When dealing with HV it used to be advised that people keep one hand in their pocket at all times. This is so that accidental electrocution will only affect one hand (and hurt like hell!) rather than flowing from one hand to the other through the heart and lungs. It is also rather wise to have an assistant immediately available if things go wrong

Thanks for the info.

lol....well, today while working on an amplifier psu I was shocked with the wall voltage. I was going to mess with a ground wire; apparently my hand had been touching a piece of exposed wire the whole time, and when I touched the ground, well, the current found a way out :? . It hurt, but not very much, and I'm still alive :-D . But yeah, I know, HV will easily kill you, I will be very very cautious.

Originally Posted by Cold Fusion

Thanks for the info.

lol....well, today while working on an amplifier psu I was shocked with the wall voltage. I was going to mess with a ground wire; apparently my hand had been touching a piece of exposed wire the whole time, and when I touched the ground, well, the current found a way out :? . It hurt, but not very much, and I'm still alive :-D . But yeah, I know, HV will easily kill you, I will be very very cautious.

When you work with a meter use that rule of one hand.

Only touch one test lead. Never hold the meter in your hand, lay it down.

That probably saved my life one day. I blew the test lead copper out of the rubber insulators. I was standing there with two hollow rubber bands, after seeing and feeling the very outrageous light show. That turned my two test leads into two inch round white fluorescent tubes.

HVAC workers sometimes hit the gas ignition wire or high voltage terminal by mistake while testing. Oil burners also have a high voltage system.

If you are holding a meter in your hand you may get a shock, through the case because, you become a plate in a capacitor.

Never stand in water. I have tested high frequency and high voltage, in water, it is pretty weird. The water separates you from ground. Just grab something grounded it stops.






Sincerely,


William McCormick