Re: [CAD_CAM_EDM_DRO] Re: capacitor

Les Watts wrote:

> Jon, Mariss,
>
> I think this is a good discussion.
>
> It's very on topic because many of us build large power supplies, often with
> surplus components, and
> face the issue of sizing components like filter caps.
>
> For others I will stick to the advice of using energy calculations
> to size capacitors. Many, many others use this method. Although I derived a
> linear "equivalent mass" expression,
> it is usually put in terms of equivalent moment of inertia:
>
> C= Jw^2/(v^2-vnom^2) where J is system moment of inertia,
> w is the maximum angular velocity in radians/sec,
> and the term in parentheses is a small voltage that the supply
> is derated by. I just pulled this bit out of a control book and
> can explain further off line if anyone needs to know.

There's more to this! This calculation is for 120 charging pulses per second.
A recent thread on UPSs made me put the two together - this is why, when I
had a power failure that left me completely in the dark for most of one full
second, my CNC system kept running right through it - without a UPS.
The computer power supply had enough holdup capacity in it to keep the
computer from losing power, the servo amps had enough capacity, too, and
the VFD that runs the spindle also had enough capacity to ride through
the outage without shutting down.

THAT is why you need a LOT more than the very minimum capacitor bank
from the calculation.

Jon