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-   -   Replacing low value electrolytics with ceramic? (https://www.badcaps.net/forum/showthread.php?t=101658)

Pentium4 12-13-2021 02:23 AM

Replacing low value electrolytics with ceramic?
 
So I disappeared from working on electronics for quite some time. I'm unboxing my ancient projects and want to resume some of them. Unfortunately, my knowledge is a little rusty.

I've always liked to do full recaps on power supplies. My cap supply isn't perfect and I do not have any more 0.47F 50V caps. I do have some ceramic caps with that value. Can they replace the lytic without issues? If I remember correctly, their max voltage drops rapidly after getting hot. Is that correct? If this isn't a good idea, I doubt the cap will cause any problems. It's by the main controller/exhaust so I doubt it will get hot or fail but I like to be thorough.

stj 12-13-2021 06:04 AM

Re: Replacing low value electrolytics with ceramic?
 
most ceramics are 60% tolerance.
i use polyester or polypropylene for 1uf and under.

Per Hansson 12-13-2021 11:18 AM

Re: Replacing low value electrolytics with ceramic?
 
Ceramic capacitors capacitance are also voltage dependent.
So the general answer to this question would be no, you can't.

PeteS in CA 12-13-2021 01:48 PM

Re: Replacing low value electrolytics with ceramic?
 
If you can get same value/voltage CGO ceramics, you won't have to worry about the temperature or voltage coefficients. If X7R, then the combined tolerance will be, IIRC, +/-20%. Z5U and Y5V are crap, IMO.

That said, the impedance characteristic will be very different from lytics.

Pentium4 12-13-2021 02:52 PM

Re: Replacing low value electrolytics with ceramic?
 
Thanks for the replies. I couldn't find anything suitable in my parts bin. I think I will just leave the cap where it is. All the other higher value caps will be replaced which should be good enough.

PeteS in CA 12-14-2021 03:03 PM

Re: Replacing low value electrolytics with ceramic?
 
Ack! COG, not "CGO".

eccerr0r 12-14-2021 03:09 PM

Re: Replacing low value electrolytics with ceramic?
 
but it is NP0?

PeteS in CA 12-15-2021 01:53 PM

Re: Replacing low value electrolytics with ceramic?
 
"COG" and "NPO" are the same thing, probably nomenclature going back more decades than I do (I think I saw the terms used in late 1950s vintage TV technician magazines).

eccerr0r 12-15-2021 02:54 PM

Re: Replacing low value electrolytics with ceramic?
 
oh I was jusr being silly with O's and 0's, you know my username... :D

Pentium4 12-15-2021 08:35 PM

Re: Replacing low value electrolytics with ceramic?
 
I needed to order parts for something else so I just ordered some 0.47F 50V nichicon UPW :)

PeteS in CA 12-16-2021 01:26 PM

Re: Replacing low value electrolytics with ceramic?
 
Quote:

Originally Posted by eccerr0r (Post 1091849)
oh I was jusr being silly with O's and 0's, you know my username... :D

OOOOOOooooooooK

eccerr0r 12-16-2021 02:02 PM

Re: Replacing low value electrolytics with ceramic?
 
000000k it is :D

TheLaw 12-16-2021 04:02 PM

Re: Replacing low value electrolytics with ceramic?
 
If you want to visualize how capacitance drops with applied DC bias voltage, you can check out Kemet's KSIM web app:

https://ksim3.kemet.com/capacitor-simulation

The limitation is fundamentally package size, and more directly, the physical amount of dielectric material contained. Since Class II ceramics are ferroelectric, they "saturate" similar to how an inductor's core might. More material means it saturates less under the same DC bias conditions.

Beware of "too good to be true" capacitance values in tiny packages. Sure you can get a 1.0uF/25V 0603 capacitor, but you better not use it above 5V, if you really need a 1.0uF capacitor.

Pentium4 12-16-2021 06:39 PM

Re: Replacing low value electrolytics with ceramic?
 
Thanks for the link, that's a pretty useful tool :)


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