Roman, thanks so much for taking up cudgels on my behalf!

Regards,

Anand.

----- Original Message -----
From: Roman Black <fastvid@EZY.NET.AU>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, February 01, 2001 03:50 AM
Subject: Re: [EE]: Non Polar Electrolytic Capacitor


> Did nobody see my original reply to this? :o)
>
> I'll repeat, when I was trained back in the
> valve days, it was taught as correct practice
> to replace NP caps with two polarised caps
> in series, reverse. It was also taught that
> that is basically what is inside a NP cap,
> and that is why they are 2x bigger physically.
> What's more the construction of some of the
> earlier NP caps was in fact two cans back to back
> with a rubber seal at each end (axial type).
> If my memory is not too rusty we disected one
> of these in class.
>
> Over the last 20 years TV servicing I have
> used this technique hundreds of times in
> situations where it was not worth the wait
> to order a specialised cap. I have NEVER
> had one fail, even in the hot overworked TV
> environment and some of these sets are still
> owned and used by friends.
>
> Diodes?? Ha ha! You guys are killin' me! ;o)
> -Roman
>
>
>
> Michael Rigby-Jones wrote:
> > > >     Hi,  I have a trouble finding a replacement part in our area..
> > > >     Does anyone know how to built a non polar electrolytic capacitor
> > > >      from two polar electrolytic capacitors,
> > > >        i need a value of 4.7 uF/ 80 volts to be used in a power
amp..
> > > >        I remember reading it elsewhere but I cant remember the
details.
> > >
> > >
> > > 1.    While you CAN do this you are probably better off using a range
of
> > > various plastic capacitor types at this voltage rating and/or "motor
> > > start"
> > > capacitors of about this value but with much higher voltage ratings.
Both
> > > these
> > > should work well in your application.
> > >
> > > If you MUST use polarised caps, try this.
> > >
> > > 2.    Connect two capacitors, each of the desired capacitance,
positive to
> > > positive.
> > > ACROSS each capacitor connect a diode (one diode for each capacitor)
with
> > > the anode connected to the capacitor negative terminal and the cathode
> > > (stripe on diode) connected to the capacitor positive terminal. That
is,
> > > the
> > > diode will conduct when the REVERSE polarity is applied to the
capacitor.
> > >
> > > Each capacitor should be the required initial; capacitance and NOT
double
> > > the value as would be the case when placing capacitors in series in a
> > > normal
> > > way.
> > > In your case use 2 x 4.7 uF caps rated at 100 volts or more.
> > >
> > > Leaving out the diodes will destroy the capacitors in a power
application.
> > >
> > I have used this method before, but for audio applications I suspect
that
> > this is a bad idea, the effect of a pair of diodes swithing on and off
every
> > cycle is definately not going to help audio quality.
> >
> > I strongly suggest either number 1) above or getting the correct
replacement
> > .
> >
> > Mike
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
> > mailto:piclist-unsubscribe-request@mitvma.mit.edu
>
> --
> http://www.piclist.com hint: To leave the PICList
> mailto:piclist-unsubscribe-request@mitvma.mit.edu
>
>
>

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu