Re: [CAD_CAM_EDM_DRO] gecko 320 filter capacitor values

Well, I can't give you really authoritative recommendations- why don't
you contact Gecko??

But what I wanted to say is don't just look at capacitance. Caps come
with widely varying ESR, and varying ripple ratings. In fact it's
typically the most difficult part. Very low ESR and high ripple rating
is very expensive, large, and these ratings are subject to age & heat
degradation.

A cap with a 100milliohm ESR will drop from 72v to 68.2v under a 38A
surge- even if its capacitance was absurdly large. The ripple rating
comes from a number of factors, one of the main ones being heat- during
a 38A current, the 100milliohm cap develops 144.4W of heat. And for
every amp-second that flows out of the cap, another amp-second must
eventually flow in which will generate a second, identical amount of
heat based on ESR. Caps don't dissipate heat especially well, nor do
they tolerate high temperatures. But of course the driver is not
getting all 38A from the cap, most of it should come from the power
supply, but then this becomes a complicated answer based on wire
resistance/inductance vs cap capacitance and ESR.

Those big "computer" caps are typically kings of ripple rating though.

Danny

dcassyc1 wrote:

> Hi all,
> I'm looking for advice on sizing power supply filter capacitors for Gecko 320
> servo drives, used to power 2 separate servo applications.
> First application is for 1 servo motor rated with these specs:
> terminal voltage: 72 VDC continuous current: 8.5A peak current: 38A. How
> large should the filter capacitor be? Would a 100VDC rating be sufficient for
> this 72 volt supply? How many MFD?
> Second application is for 2 motors with these ratings:
> terminal voltage 60 VDC continuous current 3.5A peak current 20A. Would a
> 75 VDC capacitor be sufficient for this 60 VDC supply? How many MFD?
> Is there a formula that is available to calculate the mfd value?
> Is there a recommended maximum ripple voltage?
> cheers,
> Denis
>