Re: CNC power supply question

Doug:

I would be interested in seeing some capacitor manufacturers data on
this. Aluminum foil etched electrolytic capacitors like to be fully
charged before use or after a long time in storage but I know of none
that have a problem with full discharge.

The only issue I am aware of is reverse polarity but that can't happen
with the supplies we are talking about. Some manufacturers ship
capacitors with a shorting strap across them. How can that be possible
if they can't be discharged to zero volts.

Ken

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Doug Fortune <pentam@c...> wrote:
> bull2002winkle wrote:
> >
> > The only thing I have not seen that you may want is a bleeder resistor
> > across your filter capacitor to discharge it when power is turned off.
>
> Definately not! While bleeding the cap is an ESSENTIAL SAFETY thing to
> do while building up the (unregulated) power supply (and I provide a
> temporary resistor in the kit for that purpose, for working around or
> trying to hook up a gecko to a charged capacitor is exceptionally
dangerous
> to life & limb & Gecko), ... bleeding a big electrolytic down to 0
volts
> over the long term will lessen its life considerably (from perhaps
15-20 years
> down to perhaps 3-4 years).... so says the manufacturer of my monster
> (68,000uF 80V/100V capacitors).
>
> In fact, when the capacitors arrive from the factory they all have a
> 'storage voltage' on them of 3 to 4 volts.
>
> When the capacitor is hooked up to my three G201 Geckos, and the PS
is powered
> OFF, the Geckos drain the capacitor down in about 2 minutes, but
ONLY down to
> 1.4 volts where I presume the Geckos transistor junction blocks
further drainage.
>
> This is a perfect symbiotic circumstance.... the cap is drained in a
short
> time for safety, the Gecko's LED goes out to signify the drainage
to 1.4V
> is complete, but the small 1.4 Volts remains on the cap to prolong the
> capacitors life.
>
>
> cheers
> Doug Fortune watch for -> 2.5KW 70VDC supplies in development
> http://www.cncKITS.com (for lathe & mill servo spindles).
>
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