[Prev][Next][Index][Thread]
Re: Polyethylene Capacitors
Tesla List wrote:
>
> > Subject: Re: Polyethylene Capacitors
>
> >From sgreiner-at-mail.wwnet-dot-comTue Sep 24 22:24:31 1996
> Date: Tue, 24 Sep 1996 09:24:32 -0700
> From: Skip Greiner <sgreiner-at-mail.wwnet-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Polyethylene Capacitors
>
> Tesla List wrote:
> >
> > >From hullr-at-whitlock-dot-comSat Sep 21 11:59:30 1996
> > Date: Fri, 20 Sep 1996 09:55:23 -0700
> > From: Richard Hull <hullr-at-whitlock-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: Polyethylene Capacitors
> >
> > Tesla List wrote:
> > >
> > SNIP
> > >
> > > I've just spent my
> > > > lunch hour calling around to the local Indiana plastics suppliers.
> > > > Bloomington, Indianapolis, Cincinatti and even someplace near St. Louis.
> > > > The prices were very high. A single sheet of 48"x96" LDPE 30 mil
> > > > averaged around $18 a sheet! The 60 mil averaged $34 a sheet. A
> > > > sheet of HDPE 48"x96" 60 mil was $43.96.
> > > >
> > > > Please would somebody answer my question regarding 6 mil
> > > > thickness LDPE stacked for 90 mil thickness. Will this work and
> > > > are there any pitfalls?
> > > >
> > > >
> > > >
> > > > Any comments are more than welcome.
> > > >
> > > > Big Red, HV Capacitors. Burn Baby Burn.
> > > > ITS Member
> > > > D. Gowin
> > >
> > > D.,
> > >
> > > Stack away! you could easily use 180 sheets of .5 mil poly and have the
> > > required 90 mils! It just doesn't matter. The cutting and aligning
> > > hassles are bad enough with just two sheets. If you want to lay out time
> > > and the extra effort, there is no reason why it wouldn't work.
> > >
> > > Plexiglass is rather lossey stuff.
> > >
> > > Richard Hull, TCBOR
> >
> > All,
> >
> > I note a lot of talk about air bubbles in multiple sheets. It's not as
> > bad as a single bubble in a two sheet job! With lots of bubbles in lots
> > of sheets, the voltage gradiant would distribute itself evenly and the
> > air might not even corona!!!! (lotsa sheets needed). I also note, as did
> > someone else (sorry, memory overflow), that the swelling of the capacitor
> > due to all the sheets and included air and poor adhesion would reduce the
> > capacitance over the calculated value, SIGNIFICANTLY!!!
> >
> > Again the best way is the pro way. 1 mil or thinner dielectric with end
> > foil construction in two sheet capacitors with several in series. Allot
> > of you may not realize this, but in those 40KVAC CP caps, you probably
> > don't have ten mils of poly separating the two high voltge end plates in
> > the caps! A superb amateur construction would be 5 - 10mil rolled caps
> > in series of .1ufd each! (Use a 20 megohm resistor across each pack in
> > series).
> >
> > Richard Hull, TCBOR
>
> Richard and all
>
> I have a very basic question about placing all of these rolled caps in
> series. These caps very definitely have inductance. Inductance ADDS when
> placed in series. Inductance also retards the rate of discharge of the
> total cap. It seems to me that we are defeating our purposes when we put
> a bunch of caps in series which have inductance. Wouldn't it make more
> sense to use flat plate caps with end foil terminations in all cases????
>
> Skip
Skip,
You are absolutely correct!! The flat plate capacitor is the lowest
inductance capacitor connection. However a professionally made rolled
cap of END FOIL construction is almost as good. Amateurs rarely do well
with end foil construction due to lack of proper equipment, facilities,
etc. So our rolled caps are moderately inductive (very slight). Flat
plate caps, unfortunately, are amoung the lowest volumetric efficiency
designs possible for a capacitor! (take up lotsa' room for small
capacitance.) No matter what we do we have to pay the piper with amateur
construction methods.
I hae found that as many as 3 of the old rolled style caps can be series
connected with little measurable impact on system performance provided
the leads are kept short and the caps placed relatively close to the
primary. (2-3 feet). The big boys, or pros, flatpack-endfoil roll'em and
crush them into a can connected by 1/2" long copper strapping!
Richard Hull, TCBOR