safe voltage for supercapacitors

Everyone,

I'm interested in using some kind of "supercapacitor" (e.g. double layer capacitor) as a power backup on a 5V supply which may sometimes be intermittent (can go down for short times upto 500ms). Many of these are rated for 5.5V. How close to this limit is it safe to operate them?

5V seems uncomfortably close to me, considering that the actual value may be something like 4.75..5.25 V.

I know with traditional aluminium electrolytics it's best to stay far away from the voltage rating to significantly improve lifetime. Does this advice extend to the dual layer types?

If so, I will need to put two in series (halving my capacitance), so it may become more economical to use a small battery for backup instead...

greetings, Tom

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Tom
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Hello Tom,

AFAIK they are often operated at 5V. Best is to consult the manufacturer's data. I have seen some that were rated 5.5V and recommended for backup of 5V systems.

They are totally different beasts.

Some of the 5.5V are in fact two caps in series in a common package. I always find it iffy to connect caps in series. If there is a small bleeder resistor of same value for each and their capacitances are nearly identical it may be ok. But bleeder resistors will consume power all the time even while the cap does its backup job. There are some other tricks of the trade like shunt regulators in parallel with each.

Regards, Joerg

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Joerg

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