Watson said:
[snip]
Thanks so much for all the assistance. I am amazed with your patience
with an electonic baby. It appears the Transistor is the culprit.
Maybe undersized? I replace a Radio Shack #276-1617 (tiny) with a
Radio Shack #276-2020 also known as a TIP3055. The ciruit works like
a charm. Using a digital video camera, (consumer grade (Sony)), I am
able to count a .22 second delay now compared without this delay
circuit. Thanks again and my hat comes off for your patience and
expertise with this circuit design.
I've mentione this in the past. The 2N3904 is only capable of handling
100 mA max, and that's on a good day. Because the circuit had a 10k
resistor to its base, it was a really bad day, there wasn't enough
current for the transistor (2N3904 or even a 2N4401) to fully saturate,
and the relay gets current starved also.
Remember that this is 6V, so it takes twice as much current to pull in a
given relay compared to 12V, and the relay coil is 1/4 as much DC
resistance. That puts four times the demand on the transistor compared
to 12V.
So use a decent transistor such as the 2N4401, or better yet a 2N2219 or
2N3053. And feed the base enough current to keep the transistor fully
saturated. If you can't reduce the base resistor to 1k or so, then use
a pair of transistors, but if you connect them darlington, the voltage
drop collector to emitter will be at least 1V, maybe more. You can
connect the collector of the first transistor to a 1k resistor, and then
to the +6V, and that will help.
The OP mentioned that the relay was closing, then after .2 s, was
opening again. If the transistor was toasted by excess current, that
wouldn't happen, and the relay would probably just stay open or closed.
Also, if there isn't enough current, a relay simply won't close. It
definitely won't close for a short while, and then to open back up,
since relays take more current to close initially than to stay closed.
In addition, the TIP transistor has a much lower beta than the 2N2222 he
was using, so if anything, the current issue should have gotten somewhat
worse with the larger transistor.
Simulating with 6V, a 2N2222 and a 5V relay coil with a small 100 ohm
resistance, I got max about 30mW in the 2N2222. If the relay was
moderately big, then the 60mA might not be enough, but if this were
true, using the TIP wouldn't help.
One possibility is a misconnected transistor (2N2222s have non-standard,
CBE pinouts). I haven't analyzed why a reverse connected transistor
would do this, though. Seems like it would just have a much smaller
beta, and thus the relay would stay open. The other possibility, that I
mentioned before, is a reversal of the timing cap/timing resistor. That
fits his description (the relay energizing initially for a short while,
then opening until the next cycle.)
However, without more information, it's a mystery.
--
Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.