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Caps

On Wed, 23 Nov 1994, Nikola Tesla wrote:

> >From sroys-at-Anchorage.ab.umd.edu Wed Nov 23 13:13 MST 1994
> >Received: from anchorage.ab.umd.edu by csn-dot-org with SMTP id AA00763
>   (5.65c/IDA-1.4.4 for <tesla-at-grendel.objinc-dot-com>); Wed, 23 Nov 1994 13:03:14 -0700
> Date: Wed, 23 Nov 1994 14:53:48 -0500
> From: sroys-at-Anchorage.ab.umd.edu
> To: tesla-at-grendel.objinc-dot-com
> Subject: Caps
> 
> I have an old "Industrial Instruments, INC" capacitance decade box that
> gives me a capacitance range from .001uF to 1.11uF (model DK2A) and I was
> wondering if anybody would know what voltage this would be rated for.  I 
> took it apart but I didn't see any ratings on the caps inside, and I was
> wondering if I could use this to "tune" my primary supply for power factor
> correction.  I don't want to hook it up to the 110V line and toast the caps
> if they can't take it.
> 
> 
> 
You have 2 basic problems. You are correct in worrying about the voltage 
rating of the caps.  A decade box is normally made for low voltage/low 
power applications.  Additionally, you have a current handling/power 
problem.  The AC resistance of a 1uf cap at 60 cycles is approx. 2.6K 
ohms. If you connect this in a circuit with 110 volts across it, you 
would draw .041 amps.  This may not seem like much but at 110 volts the 
power dissipation is 4.6 watts.  The capacitor would probably explode.

Even if you selected the lower capacitance settings on the box, the caps 
depending on size would probably still explode and once again I doubt 
that they would withstand 110 volts.

Dan Krones
kasper-at-kaiwan-dot-com