In alt.engineering.electrical wrote:
The 85 cent ones (CBC-125) are 1 F, 2.5 V.

No, the CBC-125 is not the one I had in mind. I should have made it
clearer. It is CBC-131, which is 85 cents in qty 10 and is .1
(point one) uf at 5 volts, not 1 uf at 2.5 volts. The CBC-125 is
$1.00 each in qty 10

Ah. I need a newer (paper) All catalog - I wasn't checking their site.

What I didn't know is implied in your next sentence:

Some of these capacitors are made for very low current (microamps,
CMOS memory) and not the tens to hundreds of milliamps you'd need
for a relay or the 10-20 milliamps you'd need for an optoisolator
or solid state relay.

What happens if you place a 10 to 30 ma load on one of those caps?

The voltage collapses. Another way to say what I said above is that
the caps have a high internal resistance / impedance / ESR.

As an example, look at pages 872 and 873 of the current Digi-Key
catalog, T051. On 872 are the Cooper PowerStor capacitors. The "A"
series has a 1 F 2.5 V cap with 0.090 ohm ESR (@ 1 KHz). DC will be
different, but: if you charged one of these caps to 2.5 V and then
shorted the leads, the initial current would be 2.5 / 0.09 or 28 A.
The "B" series (what All sells) has a 1 F 2.5 V at 0.4 ohm ESR: 6.3 A.
At the top left of page 873 are the Panasonic memory backup type
capacitors. One is 1 F 5.5 V with 30 ohm ESR, or 180 mA max short
circuit current. (As a fairer comparison with the Coopers, charging
this one to only 2.5 V would yield an 83 mA short circuit current.)
So, 10 to 30 mA might be doable with the memory backup capacitor,
but not too much more.

As is typical with OP's we may never hear how he makes out.

I don't know... now he's trying to avoid falling down a well...

Matt Roberds