Author Topic: ceramic vs film capacitors for < 1 uF 450V-630V  (Read 1364 times)

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Offline JacquesBBB

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ceramic vs film capacitors for < 1 uF 450V-630V
« on: June 03, 2015, 02:07:45 pm »

Repairing some  vintage electronic equipment, I am often faced with the  necessity to replace capacitors,
electrolytic or not, with high voltage ( 450, 630 V).

For caps under 1uF, I am thinking of using  ceramics or film capacitors, rather than electrolytics,
but I do not want to stock too many kinds.

What would you recommend ?  ceramics (X7R)  or film ?

Please do not discuss  outside from the  focussed range :  cap < 1 uF ,    voltage  from 450 V  to 630 V

Thanks
 

Offline SeanB

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Re: ceramic vs film capacitors for < 1 uF 450V-630V
« Reply #1 on: June 03, 2015, 06:00:43 pm »
I would go for film units from around 10n to 1uF, and under that 1kV ceramic capacitors. that way you have good stability with the low value ceramic units, and reasonable size for the film ones. Standardise on 630V film, as then you have a lot of room for derating with temperature. same for the ceramics, as 1kV are going to be lower change with voltage, though they will be bigger. You can use ceramic up to 47n 1kV as the size is not too bad, but for most applications in old equipment the film device is fine. will in any case be smaller than the one you are replacing.
 

Offline T3sl4co1l

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Re: ceramic vs film capacitors for < 1 uF 450V-630V
« Reply #2 on: June 03, 2015, 06:28:29 pm »
Meh, I'd go down to 1n in film.  Ceramics in MLCC format are okay up to 10n, but discs are expensive.  Anything in Type 2 dielectric is nonlinear.  C0Gs (disc or otherwise) are affordable in the <200pF range (and are usually good to *well* over rated voltage, if you feel like risking it!).

As I recall, CDE's DME series were possibly the best value as far as capacity per size and dollar.  Are they still around?  Ah, yea:
http://www.mouser.com/Cornell-Dubilier/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371?P=1z0x4lnZ1z0x6fvZ1yx4awuZ1z0x6exZ1yyirz7Z1yx4awvZ1yx4awxZ1z0zlgf&Keyword=dme&FS=True

But you're welcome to find whatever you need.  Polypropylene may be desirable for precision filters, but shouldn't be necessary for most anything in vintage electronics.  Most common application was bypass and AC coupling, both of which are low current uses; capacitor type simply does not matter, go for the smallest/cheapest.

Do make a point of replacing anything that touches the AC line, with proper X1 (line-to-line) or Y1 (line-to-ground ... if they even used a safety ground wire!) rated caps.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline JacquesBBB

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Re: ceramic vs film capacitors for < 1 uF 450V-630V
« Reply #3 on: June 04, 2015, 09:32:13 am »
Thanks Sean and Tim. These advices are helpful.

I was concerned about the film capacitors, as many of them have very short legs, not usable for  random replacement  in old equipment.
But the ones  you mention seem to be OK (I usually shop at Mouser).


As I recall, CDE's DME series were possibly the best value as far as capacity per size and dollar.  Are they still around?  Ah, yea:
http://www.mouser.com/Cornell-Dubilier/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371?P=1z0x4lnZ1z0x6fvZ1yx4awuZ1z0x6exZ1yyirz7Z1yx4awvZ1yx4awxZ1z0zlgf&Keyword=dme&FS=True
 


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