DIYbanter - View Single Post - Delay on a mains-powered relay?

wrote:

In alt.engineering.electrical wrote:

+----+ +---|AC +DC|--+--7809---+---+-------+
| | | | | | +|C2 | __|__
)||( | | +|C1 | === R1 | + |--+Sense
120 )||(12 |Rect. | === | | | |Opto |
Vac )||(Vac| | | | +|C3 P-+ |__-__|--+Loop
)||( | | | | === | | |
| | | | | | | | | |
+----+ +---|AC_-DC|--+---+-----+---+--+----+

C1 is a 1000 uf 25 volt cap. C2 and C3 are .1 farad 5 volt super caps.
(Allelectronics sells these for 85 cents each)

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

Some optos will work as low as 50 ua, from what I have read. The question
that is not answered is what his sense loop needs (how much current at
what sense voltage) and of course whether the opto will permit that current
over the full delay time.

snip

Digi-Key has Cooper PowerStor capacitors
that come already packaged as two 2.5 V caps in series to get a 5 V
rating for $4.20 to $10 quantity 1.

That's good to know. I gave a quick try searching for super caps in
Mouser and came up empty. (Doesn't mean they don't have them -
I didn't give it much of an effort.)

Your second idea, using the CBC-11/CBC-12 1 F 5.5 V memory back-up
capacitors, may or may not work.

I agree. I don't know that it will work for sure, but I strongly suspect
it will. It is guaranteed to give *some* delay - the question is, how
much. At least it avoids the question of the sense loop voltage and
current requirements. (We know it has to be small from his brief
description, but not whether an opto's vce would prevent operation.)
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 relay I specified will draw about 30 mA at ~ 4.4 volts and should
continue to stay energized down to 10 mA and possibly below that
as the voltage decays. The relay I *meant* to specify is RLY-635
(not 639). I had them both written down on my scratch sheet
when I looked up the parts. I think the 639 will work - but the
635 would give more delay. The 635 relay has a 500 ohm coil and
would draw 8.8 mA to start, and would probably still be energized
when the voltage dropped to 1.67, where it would draw about 3.3 mA.

Time will tell. As is typical with OP's we may never hear how he
makes out. But I already ordered all the parts I specified for the
second idea, and will test to see what kind of delay I can get. We
just have to wait a bit for the shipment to arrive.

Matt Roberds