AC caps for DC use

[lokeycmos]

can AC rated capacitors be used to hold a charge like a DC electrolytic capacitor? i have a microwave oven capacitor that i would like to use to hold a 2000v dc charge. it is rated for 2100VAC

 

[tcmtech]

Yep it works just fine and in fact you gain a quite a bit of peak voltage overhead as well.

AC rated capacitors are designed around the peak voltage of the AC wave but rated at the RMS value so your 2100 vAC capacitor would likely have no issues being charged all the way up to 2100 x 1.414 = 2960 volts DC! Given the safe overhead limits designed into it to work at 2100 VAC it would probably take charging into the 3500 volt DC levels without harm too.

The down side is of course the charge stored in it at that level could likely stop your heart if it went through you from hand to hand.

 

[Sceadwian]

What's the Farad rating of the cap out of curiosity?

I don't know if this is relevant to microwave oven caps but some consideration should be given to pulse derating the cap if that's what you intended to do with it. If you dump the caps full charge through a low impedance load the heating in the cap from the I^2R losses is drastically higher, and I'm not sure about parasitic inductance effects at higher currents either. So the practicality of it depends on what you want to do with it.

 

[DerStrom8]

Microwave oven capacitors are generally rated for about .1 microfarads, 1800-2000 volts. In fact, they are often charged with DC in the microwave. The magnetron requires around 4000 VDC. Since the transformer puts out around 2000 volts AC, the cap and a high voltage diode are wired as a voltage doubler. The cap charges through the diode (DC) and discharges into the magnetron. You should be able to charge the microwave capacitor with DC just fine.

How many do you have? If this is for your Tesla coil, you will probably need a lot of them to match your transformer If you're working on a capacitor bank, this site may help you. It gives you a lot of the equations that you'll need.

I hope it's ok that I'm assuming you're still working on a tesla coil

Good luck!
Der Strom

 

[lokeycmos]

Microwave oven capacitors are generally rated for about .1 microfarads, 1800-2000 volts. In fact, they are often charged with DC in the microwave. The magnetron requires around 4000 VDC. Since the transformer puts out around 2000 volts AC, the cap and a high voltage diode are wired as a voltage doubler. The cap charges through the diode (DC) and discharges into the magnetron. You should be able to charge the microwave capacitor with DC just fine.

How many do you have? If this is for your Tesla coil, you will probably need a lot of them to match your transformer If you're working on a capacitor bank, this site may help you. It gives you a lot of the equations that you'll need.

I hope it's ok that I'm assuming you're still working on a tesla coil

Good luck!
Der Strom

im still working on the tesla coil. this is for dumping 2000vdc into an ignition coil with a spark gap. i seen some youtube videos where people got 6inch sparks.

 

[DerStrom8]

im still working on the tesla coil. this is for dumping 2000vdc into an ignition coil with a spark gap. i seen some youtube videos where people got 6inch sparks.

Ah, I think I've seen some of those as well. You should be very careful, though--that could easily destroy the insulation in your ignition coil. It may work for a little while, but it is almost sure to burn out fairly quickly.

Just curious, would you happen to have the link to the videos?

 

[lokeycmos]

Ah, I think I've seen some of those as well. You should be very careful, though--that could easily destroy the insulation in your ignition coil. It may work for a little while, but it is almost sure to burn out fairly quickly.

Just curious, would you happen to have the link to the videos?

yep, here ya go. https://www.youtube.com/watch?v=q0MbY0w8F3o

yeah, i dont expect it to last too long either, but they are filled with oil. i have several ignition coils...im sure there will be some "fun factor" involved