RE: GE caps - the long answer ;-))

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi Dan,

I should have explained more...

The 42L3332 caps are fairly high current snubber types caps.  However, they 
are full metalized film rather than foil / film.  The metalization does not 
attach well to the end cap material in such caps and high peak currents 
"may" blow them out.  The super high current caps use actual metal foil in 
the plates to get very good attach and the end caps.  The 42L3332 are 
pretty strong for a full metalized cap and they often do survive and many 
people have not had trouble with them.  But, some people have had them blow 
up too.  It all depends on what the peak current in them is.  So as a 
general rule, I would not recommend them.  The full metal foil caps are far 
stronger.

Of course if one wants to use them or they are not going to super stress 
them, I can't stop them.  But I just wanted to mention the warning:

http://hot-streamer-dot-com/temp/GE42L3332.jpg

The 42L3332 was actually considered a "good" cap for about a year until 
they started failing some people.  I got a bunch of them sent to me and 
finally found the data sheet...  Then we discovered the error.  So many 
people said they worked fine...  If one is going to use full metalized 
caps, these are probably your best bet.  But just don't come yelling at 
Terry if they blow up.  Enough people have already yelled at me for having 
them on the "good" list :-((

The data sheet for the 42L3332 is at:

http://hot-streamer-dot-com/TeslaCoils/MMCInfo/GE%2042L%20capacitor%20data.pdf

Compared to the CD caps:

http://hot-streamer-dot-com/TeslaCoils/MMCInfo/942C.pdf

The dV/dT of the GE caps is 1000V/uS (remember you run them at 3000 volts too!)

The dV/dT of the CD caps is 2890V/uS.

As an example, suppose we have a tank circuit running at 250kHz and we run 
the caps at full rated voltage.  What is the peak current?

GE42L3332:  Gives 3000V/uSpeak

CD9420C20P15K:  Gives 2000V/uSpeak

V = I x t / C  or I = V x C / t  so:

GE = 990 amps peak

CD = 300 amps peak

Since the GE caps are higher value and higher voltage, they get hit with 
3.3 times their peak current (330 amps)!!!  In general, you can usually get 
away with running them at 2X the rating for a short time in intermittent 
use.  But officially, you should not run the GE caps over 1000V at 
250kHz...  I suspect Dan's string has fairly low voltage on the caps 
allowing them to survive?

The CD caps are rated for 432 amps peak so they are "just fine!!" ;-))  One 
does have to derate a little for higher frequencies and all, but the CD 
caps just happen to fall in a nice "sweet spot" for value, voltage, RMS 
current, peak current, cost.....  Thus is why we all recommend them so much 
(always).  There really is nothing that can go wrong with them unless you 
run them far over 2000 Vpeak, the frequency is super high, or the break 
rate is so high they overheat due to RMS current heating (a whole other 
animal!).  Since LTR coils that run off NSTs are well defined, the given 
charts are very safe and the reports of failures are just about zero if one 
also follows the "tips" too:

http://thegeekgroup-dot-org/mmc/constrguide.html

Forgive if we sometimes just "tell" people to get the CD caps.  A ton of 
time, effort, experimentation, trial and error, failure analysis...  has 
gone into all this stuff (6710 posts!! in the last two years, and I think I 
wrote 1/3 of them ;-)))...  So, we sometimes just hope people with "trust 
us" ;-))

I am not sure the original poster understood there is a more to MMC caps 
than "polypropylene, voltage, and value".  MMC caps are super high stress 
parts and we have to pick and choose them very very carefully!!  They also 
have to take high frequency peak currents and substantial RMS currents 
too.  It can get to be very messy trying to figure it all out.  Thus, we 
just try to get people to use the well known and proven types of caps with 
nice design charts so all the work is done.

http://hot-streamer-dot-com/temp/MMCcapSales.gif


BTW -

RMS current data is at:

http://hot-streamer-dot-com/TeslaCoils/MMCInfo/MMCPower4.html

CD9420C20P15K caps can be gotten from the Geek group:

http://thegeekgroup-dot-org/mmc/

Or from Richardson Electronics

http://www.rell-dot-com/

Lead times are usually 4 weeks from either.  Rell sticks you good for 
shipping, but if you are going to get large quantities, you can save some 
money there.  The Geek group has far better support, info, fast 
answers....  In normal quantities, they are the best source by far and they 
are our pals too ;-)))

Cheers,

         Terry



At 08:23 AM 11/9/2003, you wrote:

>I have to disagree with that assessment.  I have been using these GE
>type capacitors from the beginning
>with zero problems running systems up to about 4kW on a single string of
>these.  The only time i ever smoked one
>was while running when the coil is severely out of tune.  I would
>suspect other people have had the same thing.  But, i've run these for
>hours (intermittently of course - say one minute on time, five minutes
>off) on end (for a few demonstrations i've done in the past year) with
>no problems.
>
>Dan
>
> > Hi,
> >
> > I must mention that people have had trouble with these caps
> > for MMC use!
> >
> > http://hot-streamer-dot-com/TeslaCoils/MMCInfo/good-bad.txt
> >
> > Cheers,
> >
> >          Terry
> >
> > At 06:45 PM 11/8/2003, you wrote:
> > >They are at Allied Electronics
> > >
> > >http://www.alliedelec-dot-com/
> > >
> > >Mfr.'s Part #: 42L3332
> > >Allied Stock #: 591-6130
> > >Manufacturer: GENERAL ELECTRIC CAPACITOR
> > >Description: CAPACITORS, SNUBBER, METALLIZED POLYPROPYLENE, AXIAL, 5%
> > >TOLERANCE, .33uF, 2000VDC
> > >Current Page #: 999*
> > >Previous Page #: 155*
> > >
> > >Qty. In Stk.: 305
> > >
> > >U / M:
> > >1 Ea.
> > >Min. Order Qty.:  1
> > >
> > >1-24 $4.800 Ea.
> > >25-49 $4.360 Ea.
> > >50-99 $4.000 Ea.
> > >100-249 $3.700 Ea.
> > >250+ $3.400 Ea.
> > >
> > >Terry Blake
> > >http://www.tb3-dot-com/
> > >
> > >----- Original Message -----
> > >From: "Tesla list" <tesla-at-pupman-dot-com>
> > >To: <tesla-at-pupman-dot-com>
> > >Sent: Saturday, November 08, 2003 6:38 PM
> > >Subject: GE caps
> > >
> > >
> > > > Original poster: Koen van den Berg <cerberus_rex-at-planet.nl>
> > > >
> > > > Hi there everybody,
> > > > just another (short) cap related question: Does anybody
> > know where I can
> > > > buy GE 42L3332 capacitors (rated at 2kV DC .33uF)? One
> > lead took me to
> > > > Newark Electronics, but I can't find them there, or
> > anywhere else...Any
> > > > help would be much appreciated.
> > > >
> > > > TIA,
> > > > Koen
> > > >
> > > >
> >
> >
> >