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Re: [TCML] Capacitor differences



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
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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
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