I have an 'extended life' i.e. 7000 working hours 250V 330uF electrolytic snap-in capacitor.
It is used in a simple circuit to provide to provide a DC voltage from an input voltage of 100VAC to power 90VDC motors.
Why would the top of the capacitor start getting puffy and hollow, comparable to the touch of a membrane switch, after only 2 years of operation? I'm suspecting that occasional regenerative voltages may be causing the voltage to exceed the cap's paramters.
Mike
I meant the end opposite the terminal leads.
As the other posters have stated, i think it is just ageing plastic. As far as functioning properly, i think it still does.
The company i'm with is in the "aftermarket" biz where we repair failed legacy motor controllers. we've noticed this on many aged controllers, but it is not the cause of failure for it to be sent to us.
hollow,
years of
That is not how they are rated. Have a look
Regards,
Boris Mohar
Got Knock? - see: Viatrack Printed Circuit Designs
Maybe excessive ripple currents heating up the electrolyte?
I make 2 years = 17,520 hours, so it should have died a long time ago, even at 90V. 8-)
I'd replace it before it starts leaking or explodes. Temperature can also affect life, BTW.
Leon
"Jeroen" wrote
I second this opinion.
Or it may be overheating by the environment it is in.
If the application is within spec, but at close to the temperature and current rating, well, it is rated for only 7,000 hours and you did get
16,000 hours out of it (if your equipment is operating continuously).OTOH, if this is an isolated incident, and the conditions are well within specification, then it may just be a defective capacitor.
-- Nicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. Remove spaces etc. to reply: n o lindan at net com dot com psst.. want to buy an f-stop timer? nolindan.com/da/fstop/
I have seen radial caps do that after a while. If it is what I think you mean it is only a plastic disc covering the end of the can held in place by the shrink-on plastic sleeve covering the rest.
Why I don't know, maybe the disc expands a little with age or heat cycling.
Maybe the sleeve or can expands and contracts and pushes the edges of the disc inwards causing it to bulge.
Maybe the discs have an adhesive coating which gasses or creeps. I didn't think there would be a gas tight seal between the disc and sleeve, does it feel like there is gas pressure under it?
Whatever, the sleeve and disc on the outside of the can have nothing to do with the workings of the capacitor on the inside. I would not take this bulge as an indication of failure or impending failure. It might be an indication of how hot the caps have been running.
Oops, just re-read your post:
When you say top do you mean the end with the terminals or the other end.
If it is the non-terminal end it's just aging plastic. Might be accelerated by heat, but in itself means nothing.
You still may want to check operating condition in the case it may be accelerated by overheating.
-- Nicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. Remove spaces etc. to reply: n o lindan at net com dot com psst.. want to buy an f-stop timer? nolindan.com/da/fstop/
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