On 21/07/2019 16:29, 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?

1F @ 5F is 12.5J or 12.5 watts for 1 second. Of course, we don't know
how much of that can be used as we don't know what voltage drop your
lock can bear. It uses a battery at present which is likely to be less
than 5V I'm guessing.

So let's say we can only use 4% of that energy which seems very
conservative and leaves us with 0.5 Ws.

5uA at 5V is 25uW, so 0.5Ws would give you 20,000 seconds or 5.5 hours.

I've no idea what the self discharge of these things is, but it will be
much less than 25uA, so it sounds like a useful thing to do.

Cheers
--
Clive