Re: [CAD_CAM_EDM_DRO] Re: CNC power supply question

Ken -

The following extract from a spec sheet chosen at random, for a range of
"long life" screw terminal electrolytics:

Shelf life 2000 h at 0V +85°C, or
4 years at 0V +40°C
Operational life time 60000 h at +85°C

Seems to indicate pretty clearly that the lifetime is severely shortened if
stored at 0V.

Regards,
Tony


At 07:37 09/03/2004, you wrote:

>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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> > .
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>
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Regards,
Tony


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