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Help calculating capacitor value for a unique application.

A little background on this process.

Take 208 VAC 60HZ. Hook up to a small SCR voltage controller for variable voltage. Out to a full wave bridge rectifier. Hooked up to a resistive 35-50 Ohm load.

Here's the problem. I'm dropping to about 180VDC max at the load because there is no ripple filtering. I need a much higher voltage. I want to get this higher voltage by using a capacitor(s) across the output.

However, I have no idea what value Capacitor to use. I've searched the web and can't seem to find any calculations thet will help me. I know it will be high uF due to the voltage and current ~4-5 amps. It bascially is just a simple DC power supply but I can not find info on a supply with this high of voltage.

Any ideas???????????

Thanks...

Reply to
jjpro229
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Google for 'rectifier applications handbook'.

RL

Reply to
legg

i=C*dv/dt. You have 5 amps for i, and if your SCR controller gives you a charging pulse every half-cycle, the maximum delta-t between pulses is 1/(2*f) where f is the line frequency--generally 50Hz or

60Hz. Assume 50Hz: then max delta-t is 0.01 seconds. Now you have a relationship between C and delta-v. If you want no more than 1 volt sag, use 5*0.01 farads = 50,000 microfarads. If you can tolerate 10 volts sag (10V p-p ripple), use 5,000 microfarads.

But beware about the controller: if it triggers on a sine wave, there's very little change between triggering at 90 degrees (the top of the sine wave) and 0 degrees (the start of the sine), since the cap charges to the peak voltage during the on state. Also, beware of triggering the SCR only once; if the trigger happens before the input voltage exceeds the capacitor voltage, no current flows and the SCR never turns on that cycle.

Cheers, Tom

Reply to
Tom Bruhns

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