Of clocks and learning curves...

Ah, HA!

Thanks, Aaron.

"Aaron Coolidge" wrote in message
...
Jon Woellhaf wrote:
: Jay wrote, "Apparently the Piper master switch -- on the hot side
only --
: "powers down" after 15 seconds! Some solenoid somewhere gets thrown,
: grounding the circuit and killing power to the hot side of the master
: switch."

: What?! I'd love to see a diagram of that circuit.

The Piper master switch does no such thing. The piper master switch
supplies
GROUND to the master solenoid. Whne the switch is off, no current is
flowing
through the solenoid windings, and the master switch appears to have +12V
battery connected to it - which it does - through the solenoid windings.
When you flip the master on, it grounds the wire from the solenoid that
previously appeared to have +12V battery on it. (Just like the dome light
switch on every car except for Fords.)

ASCII schematic:

(+ Battery)---(solenoid)-----(master switch)-----(- battery)

--
Aaron Coolidge

The piper master connects the low side of the master solenoid winding to
ground. If you wired the clock to the 'high' side of the master switch, you
are powering the clock thorugh the master solenoid winding when the master
switch is off, and turning off the power to the clock (grounding the V+ clock
input) when the master is 'pn'. The clock must have a capacitor that keeps
it alive for about 15 sec after power is gone. Try hooking it up to a 12
battery, then removing power. I bet it stays on for 15 sec.

Jon Woellhaf wrote:

Jay wrote, "Apparently the Piper master switch -- on the hot side only --
"powers down" after 15 seconds! Some solenoid somewhere gets thrown,
grounding the circuit and killing power to the hot side of the master
switch."

What?! I'd love to see a diagram of that circuit.

Jon

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

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759

1. Almost universally, aircraft master switches are set up with one side of the
switch grounded to the airframe and the other side of the switch to the "cold"
side of the master switch relay (or solenoid, if you prefer). The "hot" side
of the relay goes directly to the battery (+) lead. When you turn the master
switch on, it provides a ground for the relay and thus pulls in the relay
contacts providing you battery juice to the rest of the airplane.

2. The regs allow a small circuit breaker to also go directly to the battery
(+) terminal for such things as clocks, radio memory, and other things that need
juice full-time. As I vaguely recall without pulling out the regs, you can have
up to a 5 amp breaker, but it needs to be VERY near the battery box to minimize
the amount of unprotected wire running about the airframe. Most of us use a
small L-bracket mounted directly to the battery box and a VERY well insulated
short wire from the hot side of the master switch relay to the breaker.

3. Do yourself a favor. Get a small terminal strip (NEVER would I recommend
the Radio Shack #274-656 @ 2 for $1.69 for a certificated airplane) and mount
the terminal strip somewhere between the firewall and the instrument panel in an
easily accessable spot. Wire one lead of the terminal strip to airframe ground
and the other lead of the terminal strip to a wire going back to the
aforementioned keep-alive breaker on the battery box. Then wire the clock to
the terminal strip. Trust me, you will some day need to connect a radio or
other device to the keep-alive breaker and it is a hell of a lot easier to run
two wires to a terminal strip than another wire all the way back to the
tailfeathers battery.

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

Jim Weir wrote:
snip
the terminal strip somewhere between the firewall and the instrument panel in an
easily accessable spot. Wire one lead of the terminal strip to airframe ground
and the other lead of the terminal strip to a wire going back to the
aforementioned keep-alive breaker on the battery box. Then wire the clock to
the terminal strip. Trust me, you will some day need to connect a radio or
other device to the keep-alive breaker and it is a hell of a lot easier to run
two wires to a terminal strip than another wire all the way back to the
tailfeathers battery.

Exactly! I don't understand why Jay or Jay's A&P is fooling with the
master switch or anything presently under the panel (unless he has an
existing memory keep-alive). If he doesn't take your advice and use the
terminal strip, he should atleast go directly to the battery (thru a fuse
or circuit breaker.

--- Jay


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

Jim Weir wrote:
snip
the terminal strip somewhere between the firewall and the instrument panel
in an
easily accessable spot. Wire one lead of the terminal strip to airframe
ground
and the other lead of the terminal strip to a wire going back to the
aforementioned keep-alive breaker on the battery box. Then wire the clock
to
the terminal strip. Trust me, you will some day need to connect a radio or
other device to the keep-alive breaker and it is a hell of a lot easier to
run
two wires to a terminal strip than another wire all the way back to the
tailfeathers battery.

Do you also want some sort of current limiting resistor in line with
the clock wire?
When the solenoid is activated, doesn't it draw a slug of current?
I would hate to destroy the clock electronics as a result of current
spikes.

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

Jay,
what's wrong with a $20 Timex?

Shawn
"Jay Honeck" wrote in message
news:lEurc.36031$gr.3583857@attbi_s52...
So I picked up this nifty Davtron digital electric clock/timer at Sun N
Fun.
It's exactly the same model I had in my Warrior (Model 800), and I found a
good price for it. (Roughly 4 times what it's really worth -- a bargain
in
aviation!) Our wind-up clock had become sporadic in cold weather, and I
kept forgetting to wind it anyway...

My A&P took one look at the box and said "This will be a snap to install!"
This should have set off warning alarms right away, but it didn't. We
decided to do it at the annual, when everything was already ripped apart
anyway.

So, after most of the annual was complete, Darryl (the junior A&P in our
2-man shop) dug into it. As expected, it turned out to be a real
son-of-a-bitch getting at the backside of the panel. I ended up standing
on
my head under the panel, holding the clock in place with the very tips of
my
fingers, while Darryl carefully dropped the tiny little retaining screws
onto my belly, over and over again. It was fun! Really!

Eventually, through sheer persistence, he got the damned screws threaded
in.
Then the real fun began -- wiring! The directions clearly called for the
dimmer control wire to be connected to one of the panel lights, and the
hot
lead to go directly to the battery. Unfortunately the battery was in the
way back of the plane -- not exactly handy -- so Darryl decided to wire it
into the hot side of the master switch.

This made sense to me -- which, again, should have set off warning bells
in
my head, but didn't -- as the master switch was a heckuva lot closer than
the battery.

So I picked the plane up today, after reassembling the last little bits
and
pieces. Everything looked great, the engine fired up easily, I taxied
about
40 yards -- and the clock blinked out and died....

Immediately spinning the plane around, I shut the engine and master
down --
and the clock came back to life! So, I turned the master switch back on,
and *poof* -- 15 seconds later, the clock went blank.

What the hell!?

Darryl was completely stumped, and a huddle of wise old airport bums
immediately assembled. It was obvious that hooking up to the "hot" side
of
the master switch was NOT giving us continuous power -- but why?

No one knew, and I had to get back to the hotel. I took the plane back to
my hangar, and left the wise men standing there scratching their heads.

As soon as I got back to the inn, I called Davtron. Describing the
symptoms
to them, they immediately knew the problem. Apparently the Piper master
switch -- on the hot side only -- "powers down" after 15 seconds! Some
solenoid somewhere gets thrown, grounding the circuit and killing power to
the hot side of the master switch.

They said I had two choices: 1) Run the power directly to the battery,
clear in the back of the plane, or 2) send the clock into Davtron, for
free
installation of a battery back up. This battery allows the clock to be
connected to the avionics master, rather than a "hot" wire.

I immediately called Darryl, and gave him the options. He has agreed to
fix the problem on Monday, whatever it takes, free of charge. Rather
than
take the thing out, send it to California, and reinstall it -- he's opted
to
run the wire to the battery...

Live and learn -- who'd ever think that installing a gol-danged CLOCK
would
be so hard?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

what's wrong with a $20 Timex?

Well, as my airplane is back in the shop, with the interior torn out once
again, just so they can run a damned wire back to the battery, I have to ask
myself the very same question.

The worst part is knowing that the odds of them breaking SOMETHING else
while they are working on the plane are at least 50/50...probably higher.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:
Well, as my airplane is back in the shop, with the interior torn out once
again, just so they can run a damned wire back to the battery, I have to ask
myself the very same question.
The worst part is knowing that the odds of them breaking SOMETHING else
while they are working on the plane are at least 50/50...probably higher.

Plus, the fact that this VERY simple instalation gave your A&P trouble
worries me (and should worry you). He should have known how this
electrical system works without even looking at the wiring diagram. It's
not exactly a "state secret" that clock power, and radio memory keep
alives, generally have to have a wire run to the battery. You'd better
keep an eye on this guy.

--- Jay


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

Plus, the fact that this VERY simple instalation gave your A&P trouble
worries me (and should worry you). He should have known how this
electrical system works without even looking at the wiring diagram. It's
not exactly a "state secret" that clock power, and radio memory keep
alives, generally have to have a wire run to the battery. You'd better
keep an eye on this guy.

Absolutely.

This A&P is a 60 year old, retired grocery store manager, working as an
"apprentice" with my favorite A&P, a "master mechanic" with 30+ years
experience. He just got his A&P license this past winter, but has been
working around airplanes for many years. (He owned and operated an FBO
before going into business with his best friend, the master mechanic, and is
a CFI who owned a Bonanza for many years.)

He's a helluva nice guy, very careful and thorough about most things -- but
he obviously didn't know what the heck he was doing with this clock.

The upside: He's fixing it on his nickel. The downside: Every time you
take something apart, you risk breaking something else.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"