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I wish I knew more about this stuff, but alas I do not. I have a radial lead aluminum electrolytic capacitor (rated 470mF and 25v) that died on me. Can I swap it out with one rated at 35V, or do I need to get one matching it completely? It is for a plasma, so if there is chance that 35V could cause more damage, then I would like to know!

Thanks

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Is that mF or $\mu F$? The ones with higher voltage will probably be larger, so space could be an issue, especially if the capacitor is in fact 470 mF. –  AndrejaKo May 13 '11 at 0:05
    
I agree, and to elaborate: 1 mF is 1000 μF, so a 470 mF capacitor is HUGE. mF is pronounced milifarad and μF is pronounced microfarad. –  dren.dk May 13 '11 at 7:55
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very, very similar question to electronics.stackexchange.com/questions/13091/… –  JustJeff May 13 '11 at 9:43
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2 Answers 2

Make sure that the replacement part is comparable in terms of ESR (equivalent series resistance), rated ripple current and rated hours. Don't use a general-purpose cap (usually rated for 1000 hrs or less, with ripple current specified at 120Hz) instead of a high-performance cap (ripple current specified at 100kHz, ESR in milliohms)

If the original capacitor was used in a high-frequency application (i.e. a capacitor on the output of a switching regulator) putting in a part that is not suited for the task will result in a severely shortened life for the cap and the need to replace it again once it blows up.

In general, going from 25V to 35V won't cause you a problem as long as the above parameters are comparable. Once you start getting above 35V, you'll find less and less high-performance capacitors available (the majority of low ESR parts tend to be 25V or lower).

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That is an excellent point to bring up, but his cap is rated in mF (!!), so I doubt this is a high-performance ceramic chip capacitor. –  ajs410 May 13 '11 at 17:16
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I don't think he meant millifarads. I think he meant microfarads. Also, my discussion above is specific to aluminum electrolytic caps (I have different advice for ceramic caps.) –  Madmanguruman May 13 '11 at 19:35
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The rating is a maximum voltage rating. It is not like the current rating of a fuse, the higher the rating, the better. There is normally an increase in cost from the person building them, this increase is negligible to you as a person purchasing only a couple.

You can place that one in and should actually have a smaller chance of blowing it again, this is a good thing.

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Is there any reason why would a fuse with higher voltage rating be a bad replacement for a fuse with lower voltage rating? From what I've read (do correct me if my sources are wrong), the voltage rating of the fuse shows the highest voltage on which the fuse is guaranteed to be able to open the circuit. –  AndrejaKo May 13 '11 at 0:05
    
@AndrejaKo, Fuse voltage rating is fine also. I assumed the advice about matching rating had been received because increasing the current rating of a fuse is poor practice. I will edit that in. –  Kortuk May 13 '11 at 0:11
    
The real issue with a higher voltage rating is not cost, but the design trade-offs, such as a higher ESR and larger package. –  Chris Stratton May 19 '11 at 7:08
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