Original poster: "Terry Blake" <tb3@att.net> They are at Allied Electronics http://www.alliedelec.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.com/
Original poster: Terry Fritz <teslalist@twfpowerelectronics.com> Hi, I must mention that people have had trouble with these caps for MMC use! good_bad.txt
http://hot-streamer.com/TeslaCoils/MMCInfo/good-bad.txt Cheers, Terry
Original poster: "Mccauley, Daniel H" <daniel.h.mccauley@lmco.com> 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
Original poster: Terry Fritz <teslalist@twfpowerelectronics.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.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: GE42L.pdf
http://hot-streamer.com/TeslaCoils/MMCInfo/GE%2042L%20capacitor%20data.pdf Compared to the CD caps: 942C.pdf
http://hot-streamer.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.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. MMCcapSales.gif
http://hot-streamer.com/temp/MMCcapSales.gif BTW - RMS current data is at: MMCPower4.html
http://hot-streamer.com/TeslaCoils/MMCInfo/MMCPower4.html CD9420C20P15K caps can be gotten from the Geek group: http://thegeekgroup.org/mmc/ Or from Richardson Electronics http://www.rell.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
Original poster: dhmccauley@spacecatlighting.com Allied Electronics at www.alliedelec.com I'm planning on purchasing whatever they have left in stock on tuesday morning for some big projects i'm working on this winter. So if you want to order any, make your order monday morning otherwise there may not be any left by tuesday. Dan
Original poster: "John Richardson" <jprich@up.net> Maybe go with the CD 942s instead. I ordered a bunch from www.mpaqelectronics.com for three bucks each, and they are very professional and courteous. John Richardson
Original poster: Mark Broker <mbroker@thegeekgroup.org> >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. We have had a few of the CDE 942Cs blow up as well. I think of the reported cases, only one was not officially solved as due to poor design or construction. The "anomaly" AFAIR appeared to be a manufacturing defect, though I honestly cannot remember details of this event. <snip> >V = I x t / C or I = V x C / t so: > >GE = 990 amps peak > >CD = 300 amps peak <snip> >I suspect Dan's string has fairly low voltage on the caps allowing them to >survive? Primaries with a high surge impedance should be significantly "nicer" to caps regardless of MMC cap ratings or frequency. It will be interesting to see how an MMC-Marx turns out using the 942Cs.... But I guess that's next summer's project. John R, why not support us by spending the $3.00/cap at www.thegeekgroup.org/mmc instead? Regards, Mark Broker Chief Engineer, The Geek Group
Original poster: "Jon Rosenstiel" <jonandcarol@adelphia.net> I've used the 42L's, (0.22 @ 2000V) on my 5kVA pig powered coil. Had to run 30/string so they'd last a reasonable amount of time. At 20/string their life expectancy was a minute or two. (Ends blown out) I bought them surplus, (less than $1.00 each), so having to run 30/string wasn't such a big deal. I should also mention that when using Terry's original 0.056uF Panasonic caps I had to run 15/string, ("normal" was 8 to 10/string), or they'd overheat and rupture the case. I suspect the reason I had to run so many caps/string is that my ballast, (Sears welder), was shoving a fairly large "inductive kick" into the caps, well beyond what one would think. As the saying goes..... "your mileage may vary"! Jon Rosenstiel
Original poster: dhmccauley@spacecatlighting.com Your post answered itself. The fact you said you bought these surplus sends all kinds of warning flags that you are getting inferior capacitors. Vendors typically release flawed products to the surplus market in a chance to make up some of the losses. Usually, tax right-offs cover these losses, but in a lot of instances, more revenue can be made by selling directly to surplus vendors. I made a similar surplus purchase on those "blue" Ohmmite PowerMOX high voltage resistors about a year ago for about $0.50 each for 10MEG resistors. I was surprised to see they were failing left and right when I was using them with some MMCs i built. I called the vendor with the lot number (printed on the resistors), and they indeed did scrap these resistors due to an internal manufacturing flaw. Dan