I've had a few failures of these recently. Used round a bridge rectifier - for RFI purposes, I'd guess. They were the normal sort of wax covered types. In all three cases, one had shorted.
Is there anything better to use for this?
--
*If you think this van is dirty, you should try having sex with the driver*
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
driver*
Wax covered?
Move them away from any heat source? I've not known them to be a trouble child. If you choose MLCC replacements be sure to choose the correct class of dielectric. Class COG/NPO contain neodymium, samarium and other rare earth oxides and have a negligible aging rate.
-- Live Fast, Die Young and Leave a Pretty Corpse
In these cases they were pretty low powered supplies - 100 mA or so and quite open so heat shouldn't have been a problem. Although they were mounted close to the diodes.
Not exactly that as they'd lasted quite a time. But like all these things if slightly more expensive ones last even better it makes sense.
Thanks.
--
*He has no enemies, but is intensely disliked by his friends
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
Any chance it was an MOV (metal oxide varistor) instead of a disc cap? Kinda difficult to tell from your description. "Normal"? "Wax"?
If the bridge has several diodes in series for each leg, you'll need equalizing caps and resistors to make sure that the voltage is equally distributed among the series connected diodes. That means they should all be equal value.
If not, just get a higher voltage rating. Shorted disc ceramic usually means that some high voltage punched through the dielectric or that the plating has exploded and sprayed conductive crud around the insides.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Or it might be a NTC surge limiter. If these are in series with the AC line, it limits the initial charging current of the DC input capacitors. They protect the line fuse.
I havn't seen too many MLCC's that have been waxed or potted but if they vibrate in a audio detector or IF stage and introduce noise. Waxing them would be one way to dampen vibration. Plus I think Dave knows the difference between an MOV and a MLCC dontcha think?
-- Live Fast, Die Young and Leave a Pretty Corpse
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r*
=A0 London SW
Replace with known good quality parts. Total length of leads including capacitor disc diameter should be kept as small as possible--1cm is very desireable. They work even better with about 22ohms 1/4 or 1/10W in series if there is room.
Neil S.
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The usual RF bypass disk capacitor for AC would be a 1kV rating (just in case of surges) and they last nearly forever in my experience. What value are they? If it's high capacitance (like, over .001 uF) it might be a multilayer type, and THEY can short out.
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