My experience - shared for mine and other's education and offering of opinion.
This past weekend, I was working on the wiring of my flap position sensor for my
two-speed elevator trim circuit. The two-speed trim circuit essentially switches
a low speed set matronics governor for a high speed set one via a pair of
4PDT relays whenever the flaps come off the upstop.
As I was testing the detector switch - I got 'bit' by something that felt like
house current (done that too!). Not knowing what was going on, I repeated the
test...with identical results.
OK, break out some of Bob's literary work - read-up and put in some diodes across
the power terminals of the coil.
Re-reading made me think that in my case, the diodes may be even more important...in
Bob's writings (Paraphrased) "the absence of the diode presents the opening
switch with the spike"; in my case, I have a couple of things wired up within
the master switch... I'm thinking that in my case the master switch would
'see' the spike...along with anything else that is left on when I turn off the
master.
I know that the 'real' airplane stuff should be able to live in this environment
and should not produce this environment either - however in the OBAM world,
I can put in non tso'd trim servos and indicators (of which I have had a couple
of them mysteriously blow one of their indicator lights) which are pretty good
gear as far as I'm concerned - they just haven't spent the money and gone through
the certification process.
Got the diodes and will be putting them in this weekend. Is it possible that I'm
allowing a spike to wander around my electrical system by turning off the master
with some of these relays energized?
Your thoughts please,
Ralph Capen
