Re: [CAD_CAM_EDM_DRO] Re: What size capacitor should I use?

>Attn CNC power supply people...Please DO NOT put a resistor between
>your bridge rectifer and your capacitor...Because of the time
>constant increase (T=RxC)x5, you will render the recovery of
>capacitor voltage to be to long in time to be of any use to PWM
>drives...
>
>T = time in seconds
>R = resistance in ohms
>C = capacitance in farads
>X 5 = 6 time constants for a full charge
>
>example... Power supply has 30,000Uf and you add a .5 ohm resistor.
>C = 30,000Uf is 10,000 to the minus 6 farad.
>R = .5 ohm
>T = C x R
>T = .03farad x .5 ohms = .015 seconds for 1 time constant.
>It takes 5 time constants to charge a capacitor...So..
>5 x .015 seconds = .075 seconds for capacitor to recover...
>.075 seconds = 75mS = 75000uS
>
>We are PWMing around 22khz or 22,000 cps..At this frequency each
>chopped wave can be as small as 1/22,000 = .0000454 seconds...Or..
>.0454mS....Or 45.4uS
>
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