Capacitor Discharge

1 KV Diode for 1 KV is border line practically.

Yes theoretically it is ok.

Theoretically you can draw unlimited current from a diode so long you maintain its junction temp at the specified value.

So it is the amount of heat energy generated at junction that matters.

Total energy released by capacitor=1/2(CV^2) joules.

This mean the size of capacitor can be up to the limit where you can maintain the temp of junction with in the specified safe value.

You can calculate it if you know

1 Specific heat of complete diode as a whole,

2 rate of the heat dissipation.

The limitation is how much current you can put through the diode before it blows. So, get that info from the data sheet. The current will be limited by the resistance of the path, which will be the ESR (effective series resistance) of the capacitor (again, check the datasheet) and the ON resistance of the diode, which may be on the data sheet, and may or may not be reliable for this kind of use.

I would suggest adding a resistor in series and use it to keep the peak current, (1000V/R) well below the max specified for the diode. That way, you can use as big a cap as you want, since the capacitance no longer determines the current. 1/2 the maximum diode current is a good target, for reliable operation.

If your desire is to dischage the capacitor why not forgo the diode and use a resistor?

At 1kV this is not a typical board level cap. I imagine the cap has some current capability that must be measured. Charge the cap and measure the max short circuit potential. The diode at this point should be sized for the cap. Sure you can calculate values, but the only way to really know is by experimenting and repeating until values are constant. Beware of the potential and of the discharge arc and the possibility of the capacitor rupturing. The diode also will be subject to heating and may need heat sink to protect the diode. This can be a destructive experiment. Good luck.

Thanks for replying to my quesion.

You said that a cap has a current capability and sugested finding it by experiment. You also said that the values can be calculated. How can i calculate the current capability of a cap, this will let me know wht to expect when i experiment.

Thanks

At this size of discharge don't even think about it you will very likely do serious harm to your self. The chances are you will destroy the cap and diode in an instant.

If you must do this then take serious safety precautions.

It is potentialy lethal.

Certain Capacitors and diodes are made for this kind of discharges. Think of magnetizer for the magnet of high MMF.

Don't worry, continue, choose the right capacitors and make sure all screws are tighten well,

All the Semiconductor devices have a burn-out specs: ie I^2xt where I is the current thru it & t= time

Diodes & other devices are not rated for temp, Current, Wkg Voltage singly but no one rating can be exceeded from its rated value.

Capacitor is an Instant_Discharge Component## & may dump the total of its energy [C.V^2] joules in very small time, almost in micro-seconds.

Before you notice it may have gone.

##[see the Flashes etc where the battery voltage & AH are much smaller but charge a Hi-voltage Hi-capacity Capacitor in a longer time to get full energy, then discharged through Flash tube, which itself is an instant-discharging device]