So the common wisdom is that the important characteristics when replacing a general-use electrolytic capacitor are:
- capacity
- voltage
- temperature range
- physical size
- polarity
The added advice then is that if those can’t all be met, picking one where the voltage is higher is usually fine. E.g. a unipolar 10µF, 10V, 85⁰C cap can be replaced with a unipolar 10µF, 25V, 85⁰C one (if it fits physically). One could of course also use a 105⁰C component.
However, I was wondering if that voltage-advice was subject to caveats. E.g. if I replace a 10V rated cap with a 100V one, what are the downsides? If I understand correctly, straying too far from the rated voltage may result in the electrolytic not being maintained/“refreshed” enough, and thus may lead to premature failure. But I am not sure if that is true or to what extent. Any advice appreciated.
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Welcome to the forum.
Down in the very low electrolytic capacitance range (<100uF), on circuits designed this century, the original designer may have needed specific performance for one of the other less used specifications e.g. ESR.
If that is the case then substituting a higher voltage may not work as well as the designer intended.
For circuits using normal range electrolytics (100uF to 10000uF), or designed last century, it is a virtual certainty that the voltage rating was only chosen for lowest cost and size. With those type circuits a 100V capacitor will almost certainly work fine in a 10V application.
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Thanks for your reply, Paul. The current project I have that made this question come to my mind again is a recap of a 90s Sony amp. I figure the critical caps are the ones in the PSU to provide impulse current (and smooth ripples) and anything that is involved in the signal path. fortunately, the original parts are all Nichicon and Elna, and there are no obvious failures. I’ve tested most of the signal-side caps and they are all within acceptable bounds (capacity slightly lower than spec1, but not more than 10% off; ESR all <2Ω, most <1Ω). The few that are left are hard to access and so will have to wait.
Given that, I am debating myself if recapping is really necessary, or if the cost/time (and potential of messing things up) outweighs the peace of mind new caps would bring. OTOH, I have the whole thing apart anyway for a good clean and to check for dry joints, so I might as well…
1 An old-timer once told me that as caps age (and the electrolytic goes), the gap between plates narrows, increasing capacitance, so a slightly-low value on a used cap is usually a better thing than slightly high. Not sure if it’s true, but I’ve been flying by that general rule for a while now.
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I’ve never gone for the re-capping fad myself in the 55 years I’ve been repairing electronics.
My general rule is to only replace parts that test bad since I consider myself more engineer than technician.
In the 80s this rule once made me spend the cost of an OK used car on an capacitance tester that measured ESR before replacing a suspected bad DC blocking film cap in a 13" TV (it did read high ESR after only 8 years usage).
The exception to this rule for me is electro-mechanical parts (e.g. pot, switches) where I can literally feel the wear and tear so I know it will fail sooner rather than later.
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My main motivation for preemptive replacement would be to avoid a failing cap taking something with it that is harder to replace. Granted, in this case (90s Sony amp) it’s unlikely, but I’ve had to junk turntables from the 70s because a cap took out some silicon that was just plain unobtainium 40 years after the initial production run.
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