Re: What size capacitor should I use?

> Are you suggesting that you are able to discharge your entire

> capacitor through your servo in 45 microseconds? If so, I think

> steppers are truely enormous.
>
> regards
> CS

> cnc_4_me wrote:
>
> >Attn CNC power supply people...Please DO NOT put a resistor

> >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
> >
> >
> >
> Are you suggesting that you are able to discharge your entire

> capacitor through your servo in 45 microseconds? If so, I think

> steppers are truely enormous.
>
> regards
> CS