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

cnc_4_me wrote:

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>>Are you suggesting that you are able to discharge your entire
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>filter
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>>capacitor through your servo in 45 microseconds? If so, I think
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>your
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>>steppers are truely enormous.
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>>regards
>>CS
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>No, i am not...45uS is simply the smallest unit of time in a average
>PWM system...
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True, but your analysis suggests that each PWM pulse requires a full
recharge of the filter cap.

I don't think the PWM frequency will be of any consequence here
(presuming the capacitor has low enough ESR to supply the necessary
current) What's important is the average current draw, any how much it
discharges the capacitor before the next AC charge cycle (which is never
more than 0.01 seconds away). If your capacitor is too small the
current and voltage ripple will be quite large. A very large
capacitance will keep voltage ripple at a minimum, but you'll still need
to be sure the current ripple is within the specs for the particular
capacitor you are using.

If a series resistor limited the charge rate of the capacitor to less
than the average current draw of the system, then you'd have a problem.
Otherwise it might not be a bad idea.

CS