Jay,

I have one of those older dimmer systems, and it is no picnic. The old one is
just a power rheostat wired in with the lights. The rheostat heats up because
it handles all the power. That transistor circuit simply controls the current
by using the transistor to amplify small current changes in the rheostat. The
result is the rheostat needn't be a custom high power one, and it won't burn out
as easily. The rheostat only dimmer gets hot to the touch if you have more than
just the original overhead light and compass light on it, and probably can't
handle a full panel worth of lighting. I'd trade the simple older dimmer for
the transistorized one if it we cheap and painless to do. When my dimmer does
go, or I add more lighting to the panel, I'll probably opt for one of the pulse
width modulated ones (those are much more complicated than the piper pass
transistor, but they also dissipate very little power).

Jay Honeck wrote:

Good points John, and I agree wholeheartedly, but can you expect every
A&P to fully understand each and every detail? I don't care to pay
for an A&P's education, but it's almost like saying that you obtained
your 30 years in a few months.

My A&P is the best engine and airframe man I've seen.

However, when it comes to electrical, even he will admit that he's a "figure
it as you go" guy, even though he works on DC-9s most of the time.

Personally, I think the dimmer circuitry in the Cherokee is perhaps the
dumbest thing I've seen in aviation. Even I, as a total neophyte, can see
that the system is hopelessly obtuse.

Strangely, older Cherokees had a much simpler dimmer circuit. I wonder why
Piper made it so complex later on, and I wonder if they've corrected this
mess in their new planes?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

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