On 21/07/2019 20:18, Tim Streater wrote:
In article , Harry Bloomfield
wrote:

I've never used a supercap before, though I have had one kicking about
here for a long time, a 5v 1 Farad. I have an old code entry lock,
which I am looking to install, which runs on 5v and needs a battery to
maintain its code memory at 5uA.

I don't expect the mains supply to ever be off for long, but with no
supply at all available to the lock, it reverts to a not very secure
entry code of '0'.

Would the cap do the job? Anyone any experience of using them?

Well you need to do the sums. How much charge is stored in it when its
up to 5v? Then, at what lower output voltage will the code memory lose
its data? How much charge does that equate to? So your "available
charge" is the difference, and given you said 5µa, you can work out how
long you can get that current before the output voltage drops too low.

I expect the formulae you need are in Winky somewhere.

Charge in joules is, IIRC, ½CV²...

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