Miles Mauldin wrote:
Hi All, I know everyone talks about the 942C series capacitors and the price of them. I was wondering why one would not use the 940C series since it is rated at 3kV and would require fewer in a string to hit the target voltage. 940C30P15K-F $3.14 940C30P15K-F $3.14 940C30P15K-F @ $3.14 942C20P15K-F @ $3.23 Thanks, Miles _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
Hi Miles,Although the CD 940C caps use self-healing metalized film, they do not use metal foil to provide a low resistance connection to the wire leads. Instead, they use sprayed metal to contact the thin metalized layers. As a result, they do not handle high currents very well. In Tesla Coil use, they'll rapidly overheat and fail. The 942C caps use foil and metalized film to create more robust end terminations, while still retaining self-healing technology.
Back in the early days of MMC development (2003) Terry Fritz conducted a number of tests to confirm which capacitor types performed well, and which did not. He found the following:
KNOWN GOOD MMC CAPS =================== Manufacturer Part Number Voltage (VDC) Value (uF) ------------ ----------- ------------- ---------- Cornell Dubilier 942C20P15K 2000 0.15 Cornell Dubilier 942C20P10K 2000 0.10 Panasonic ECW-H 16563JV 1600 0.056 Seacor KP25 1600 0.047 SB Electronics 16PSS50 1600 0.050 Arcotronics RS-114-474 1500 0.047 Arcotronics KP1-72 1500 0.10 Wima FKP-1 1600 0.0068 Wima FKP-1 1600 0.033 Wima FKP-1 1600 0.10 Phillips KP-MMKP 2000 0.0047 Phillips 376 KP/MMKP HQ 1600 0.056 Mallory PVC 1611 1600 0.010 Illinois Cap. 683PPB202K 2000 0.068 KNOWN BAD MMC CAPS ================== Manufacturer Part Number Voltage (VDC) Value (uF) ------------ ----------- ------------ --------- Cornell Dubilier 940C20S33K 2000 0.033 G.E. 42L4102 3000 0.01 G.E. 42L3332 2000 0.33 Note: Full metal "film" caps fail at the end plates. You want "film/foil" caps like the CD 942 series. Thanks to Garry for helping discover this (the hard way...)!! G.E. 42L series caps are all metalized and not recommended. they have higher current rating than most but people still have trouble with them. Bert -- ******************************************************************** We specialize in UNIQUE items: coins shrunk by ultra-strong magnetic fields, Captured Lightning Lichtenberg figure sculptures, and scarce technical Books. Please visit us at http://www.capturedlightning.com ******************************************************************** _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla