Of clocks and learning curves...

EDR
shared these priceless pearls of wisdom:

-
-Do you also want some sort of current limiting resistor in line with
-the clock wire?

Not unless the manufacturer of the clock put such a device in the installation
instructions. I can't tell you how many hours I've spent troubleshooting
problems that people "engineered" into their own systems by "making it better"
than the designer intended.

If a company manufactures aircraft clocks (or radios, or other electrical
devices) it is understood that there are going to be times when a spike comes
down the path. We all design in protective circuitry or some sort of spike
limiter/crowbar to limit the nasties. There are tens of thousands of articles
written on surge/spike suppression and there are tens of thousands of ways of
designing in that protection. What we CANNOT design in is protection from
somebody putting in a resistor or some other device that honks up something that
we did not contemplate.



-When the solenoid is activated, doesn't it draw a slug of current?

Not really. It is just another relay, albeit a pretty good sized one. And, it
is VERY close to the battery and wired with VERY heavy wire. Close and heavy
minimizes the inductance, and since the induced voltage is equal to L * di/dt,
and with that huge spike suppression capacitor called a battery on the line, the
spike should be relatively benign. NOTHING to compare to a starter motor firing
up.


-I would hate to destroy the clock electronics as a result of current
-spikes.

And the clock manufacturer would LONG since have been out of business if his
devices didn't take spikes into account.

Jim

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com