$429 Dimmer Switch

Actually, they are a little simpler to design than the old analog beasts, in
that you don't have to do a lot of thermal worst-case analysis. And, the
current limiting is a hell of a lot easier to do.

Watch out, though, that the person who designed it understands RFI and how close
to the noise margin the Loran is. You'd be surprised how many designs have
their switching frequency a submultiple of 100 kHz. and wonder why the loran
(and everything else harmonically related) goes Tango Uniform when the lights
come to life.

Also, you need to understand that switching frequencies on the order of 30 Hz,
90 Hz., 150 Hz., and 9960 Hz. will honk up the avionics also. The hell of it is
that radio manufacturers do a great job of shielding their product against this
sort of RFI, but then run a wire from the dimmer port directly to the lights,
letting any crap on the dimmer wire merrily radiate throughout the radio.

Jim

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).



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

Ray Andraka wrote:

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).

The next step in the evolution is to get rid of all those incandescant
bulbs and replace them with LEDs. Lower power consumption for the same
light output, and they never burn out.

Three words...

Newly graduated engineer.



I wonder why
-Piper made it so complex later on,



Jim



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

Jay Honeck wrote:
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.

Ray has explained to you, twice in this thread, why transistors are used.
If you can't understand the technology, stop commenting on it.

--- Jay


--

__!__
Jay and Teresa Masino ___(_)___
http://www2.ari.net/jmasino ! ! !
http://www.oceancityairport.com
http://www.oc-adolfos.com

Ray has explained to you, twice in this thread, why transistors are used.
If you can't understand the technology, stop commenting on it.

Wow, we normally can't find anyone here to defend the high-tech 1974 Chevy
Nova technology found in my Piper -- thanks!

Your view is, um, refreshing, somehow. Kinda like the Amish, I suppose, but
I guess I could get used to it.

Actually, flying a 30 year old airplane, I have little choice. :-(
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

: 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?

I won't debate the older vs. newer circuit too much, except to say that it
moves the heat loss from a rheostat to a transistor. Both are linear "regulators",
but due to the changing load requirements a resistor makes a very poor choice. My
plane's the older variety, and the lights are off for about 75% of the travel of the
dimmer. The other 25% goes from off to full bright, and makes the last 25% of the
rheostat coils have to dissipate all the power.

They're both a bit clunky (PWM being more efficient, but prone to noise as
previously mentioned). Aside from this being an AIRPLANE, the transistor setup is
CHEAPER and "better" from the linearity and robustness standpoint (TO-3 package 2N3055
is a tough transistor that can dissipate a lot of power). In reality, the 20W or so
max is negligible power lost (1-2A draw) and a decent compromise for complexity
and noise immunity. Still better are LEDs... less power, and even a linear regulator
won't have to dissipate much.

Hope that helps describe why they went to it.

-Cory



--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

Hope that helps describe why they went to it.

Thanks, Cory!

Do you know if there's a legal way to put LEDs in my plane?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Oh no! Someone having the audacity to disagree with King Weir!
That'll make him spit out his morning latte! Stand by for the flames.

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.


Well, I'm truly not looking for a flame war, and I really meant that little
blurb about a "confirmed lingerer"....just couldn't help myself.

It seems that in a discussion group like this there are always very vocal folks
that are always willing to tell you that their way is the better way and that
would have you believe that all mechanics and IA's are crooks or incompetent.

I find it very dangerous that there are folks out there in internet land that
spend their time spouting ways to decieve the FAA and get around the regs,
rather than trying to help folks work within the regs.

Just to clarify a few things, I believe that a good mechanic armed with a
multi-meter and schematic of the Piper instrument light system could do the
same. It does seem, however that many of my brothers and sisters in the biz
just don't have a good grasp on electricity in general and transistors in
particular.

Additionally, in my shop, if I happen to assign a green mechanic to a job such
as this and it takes him/her 5 or 6 hours to trouble shoot and repair.....I
WILL NOT bill the customer this amount. I will bill what I believe is an
adequate and fair amount. The up-side to this is that my mechanic will now be
"trained" and next time around, I won't lose my shirt on the deal. I think
what I was trying to say was that the $429 dimmer was a bit out of line, then
Mr. Weir piped in with his "better way of doing things" which is a tremendous
idea for a home built, but has no place in a certificated ship.

I actually do this on a regular basis. I will assign a green mechanic to a job
like this and with a few well placed nudges and a watchful eye, encourage
him/her to get a copy of the schematic and go troubleshoot. When the job is
done, the customer gets a bill based on what I think it would have taken ME to
fix the problem.

Interestingly enough, there have been times that I've cut a labor bill by
better than 50 percent and still caught hell from a customer. Go figure. (all
you accountants out there must understand that cutting a labor bill by 50% puts
me in the hole, figuring salarys, overhead, etc. etc). I just find it
interesting that nobody complains about the auto dealerships that flat rate
maintenance labor. You know, the guys that fix cars at the local Ford (insert
favorite car type here) dealership take home more pay than my mechanics. They
get about the same hourly rate, but a fair auto mechanic can turn in 60 to 80
hours in a 40 hour work week.....is that fair? Those hours are paid for by
YOU....the consumer.

What makes me so mad about this is the fact that these guys have almost no
liability......I could lose my home, my car, my job and every other thing I own
if a court/jury even THOUGHT I was neglegent......and guess what, jurys don't
make decisions based on regulations. Been there, done that.

We don't flat rate and I think I'd get out of the biz if we did.

The bottom line is....if you feel you're being taken by your mechanic, take
your maintenance dollar somewhere else. Just remember however that a
mechanic/IA that dosen't do his/her job exactly with the regs, isn't doing an
adequate job for you.....You as the PIC (per the regs) have the final
responsibility for the airworthiness of the aircraft you fly. My job as your
mechanic/IA is to keep your aircraft airworthy mechanically as well as
paperwork wise....and I am OBLIGATED under the regs to do both.

I really do understand though, that there must be some give and take, because
if I can't generate a pool of satisified customers, my shop will cease to
exist.

Phew....thanks for this opportunity to vent.......back to lurk mode for me.

The bottom line is....if you feel you're being taken by your mechanic,
take
your maintenance dollar somewhere else.

Thanks for the input, John. (You really *do* need to de-lurk here more
often.... ;-)

I have taken my business elsewhere in the past, when I truly felt I was
being ripped off. However, my current mechanic is an incredible guy, has
taken us out on his boat, has welded things for me, gratis, has helped me
bead-blast P-51 parts for our Mustang Suite, gratis. The list of favors
goes on an on.

He works ten times faster than the "corporate" shop on the field, although
perhaps not in this isolated case.

I will stick with him through one bad experience.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Had a double helping of bitch flakes this morning, did we Stu?

Jim


Stu Gotts
shared these priceless pearls of wisdom:

-Oh no! Someone having the audacity to disagree with King Weir!
-That'll make him spit out his morning latte! Stand by for the flames.


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