Re: Capacitor hunting

Hi Paul,

I spun by the junk yard and found a 68,000 75 V cap today !
it was connected to a couple huge transformers and there is only one
label 48 VDC. It's great when someone else did all the leg work on
matching the components. ($20.00)

Once I get it in and dusted off, I'll take some pix and hopefully
find out what voltage these transformers are.

It is ready to go, then those NEMA 34's are prime for this puppy !

I may have the electronics set for the small router table. 18x30
with 14 x 12 work surface.

Thanks to all you who responded.

Dave

--- In CAD_CAM_EDM_DRO@y..., "Paul R. Hvidston" <paul@7...> wrote:
> I found a bunch of old 12,800, 75V working/100V surge capacitors at
an
> industrial surplus sale for peanuts. I had to reform the dielectric
by
> applying the DC voltage through a high-value resistor, and letting
them
> "soak" for a few hours to see which ones would recover. All but
one were
> restored to operation. I'm using a pair on my 72 volt, 15 amp
supply. Don't
> go way overboard on capacitance as it will appear as a dead short
to the
> rectifiers at power-on and pop your bridge if you're not careful.
>
> As far as ratings are concerned, you can choose filter capacitors
with a
> working voltage about 5 or 10% above your maximum voltage. The
surge-voltage
> rating, which is typically 30% higher, will save your cookies for
short term
> voltage rises (electronics not withstanding). Don't, for example,
choose a
> capacitor that's double your max voltage. It's not good for the
capacitor as
> it tends to deteriorate the dielectric more rapidly, just like too
much
> voltage.
>
> Another tip about ratings. Choose a bridge rectifier with a PIV
(peak
> inverse voltage) rating greater than 1.414 times your transformer
secondary
> for bridge configurations (2 wire), and 2.828 times your transformer
> secondary for full-wave center-tap configurations (3-wire). A
minimum bridge
> PIV rating of 2 times your secondary RMS works. Current capacity
should be
> at least 2 to 3 times you transformer secondary rating (just to
keep it
> simple). A 100 PIV, 35 A Motorola bridge cost me about $5.50 at a
local
> electronics store. The expected maximum voltage for a bridge power
supply
> will be (1.414 times the transformer secondary RMS voltage) minus
about 1.5
> volts bridge drop.
>
> Regards,
>
> Paul R. Hvidston, N6MGN
> ACKSYS Engineering
> Upland, CA