Re: HV power supply

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ben McMillen by way of Terry Fritz <twftesla-at-qwest-dot-net>" <spoonman534-at-yahoo-dot-com>

Yes. All of it makes perfect sense... I SHOULD have known
that already ;) 

Coiling In Pittsburgh
Ben McMillen

--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <Tesla729-at-cs-dot-com>
> 
> In a message dated 5/12/02 11:01:24 AM Pacific Daylight
> Time, 
> tesla-at-pupman-dot-com writes:
> 
> << I may be wrong, but isn't overvolting any type of
> capicitor
>  a BAD thing?
>  
>  Coiling In Pittsburgh
>  Ben McMillen
>   >>
> 
> Hi Ben, all
> 
> Yes, overvolting a capacitor is bad, but a large
> capacitor imparts
> a big load on the power supply so until the capacitor
> begins to get 
> fully charged, the power supply will see the capacitor's
> low impe-
> dance as a near short which will make the actual voltage
> across
> the capacitor much lower than the rated output of the
> power supply.
> As the capacitor gradually charges, the voltage across
> the capa-
> citor will gradually rise. I used to charge large
> electrolytic capaci-
> tors (400 volt, 2500 uFD) with the rectified output of an
> MOT. MOTs
> usually put out ~2000 volts, but a discharged cap of this
> size is ba-
> sically a dead short until it begins to take on a charge.
> I had the 
> input of the MOT controlled thru a variac but would turn
> the variac
> up to at least 30% (probably 700 volts or so). I of
> course had a 
> volt meter at the terminals of the capacitor(s) and when
> the volt-
> age measurement at the cap's terminals reached the rated
> 400
> volts, i would simply shut off the power from the MOT.
> That's basic-
> ally what I'm trying to do with my 10 kV,10 kJ quarter
> shrinker/ can 
> crusher capacitor bank now. If the supply voltage is only
> say 10
> kV, then since it takes 5 RC constants for the cap to
> completely
> charge to the supply voltage, it takes a looong time for
> the capa-
> citor's charge to to completely equal the voltage of the
> power sup-
> ply. The caps charge voltage can reach 80% of the power
> supply
> voltage pretty quickly, but it takes almost forever for
> it to reach 
> > 99%. If the supply voltage is say only 20% higher than
> the cap
> voltage rating, the cap could be charged relatively
> quickly to its 
> rated voltage and then removed from the power once its
> rated
> voltage has been reached. Of course, the impedance and
> current
> capacity of the power supply would also have a bearing on
> how 
> quickly the cap could be charged, too (a 50 mA supply
> will charge
> faster than a 20 mA supply, assuming all other factors
> equal)
> 
> Does any of this make sense :-)??
> 
> David Rieben
> 
>