Re: [CAD_CAM_EDM_DRO] gecko 320 filter capacitor values

HI Danny
I found the capacitor rating method off Gecko's site. Thanks for the info on
ESR, I never was aware of it before and the heat dissipation that takes place
too. Luckily I made accomocation in the cabinet layout for plenty of forced
ventilation.
cheers,
Denis

On Wednesday 25 February 2009 21:28:57 Danny Miller wrote:
> 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