Of clocks and learning curves...

Aaron Coolidge wrote:

The Piper master switch does no such thing. The piper master switch supplies
GROUND to the master solenoid.

Indeed. Arn't all aircraft this way? My Bonanza certainly is.


--
Frank Stutzman
Bonanza N494B "Hula Girl"
Hood River, OR

Jay Honeck wrote:

Also, why is there a 7-second delay after turning the master switch on?

The 7-second delay is probably in your clock. That's how long the clock
continues to run after it's power is removed.


Here's how it works:

1. The clock is connected to the "hot" side of the master.

The "hot" side of the master does not go to the battery; rather, it goes to the
COIL(-) of the master contactor. The battery goes to the *other* side [coil(+)]

Your clock is thus not connected directly to the battery. The COIL of the
contactor is between the battery and the clock.


2. It works fine with master "off"

Yes, because it's receiving voltage *thru* the COIL (a resistance of several
tens of ohms or so.) It works just fine.


3. Turn Master Switch "on" -- works fine for seven seconds.

The master switch connects the coil(-) to GROUND. The voltage at the "hot" side
of the master (and the clock) goes to ZERO. Current flows from the battery thru
the coil and switch to ground; causing the master contactor to close (you'll
hear the "clunk" if you listen) and the airplane's electrical system is energized.


4. At seven seconds, the clock goes out.

Because that's how long the clock runs after power is removed.


5. Turn Master Switch "off" and the clock comes back on.

Yes, the COIL is un-grounded, the contactor opens ("clunk") and the electrical
system is de-energized. The voltage at the "hot" side of the master returns,
and the clock runs again (unless it's wiped out by the inductive kick-back from
the coil


What's going on? Why is this circuit set up to do this?

Ask the idiot (Certified Mechanic?) who wired in your clock that way!

Frank Stutzman wrote in
:

Aaron Coolidge wrote:

The Piper master switch does no such thing. The piper master switch
supplies GROUND to the master solenoid.

Indeed. Arn't all aircraft this way? My Bonanza certainly is.


I'm no A&P but if that's the case, then Jay's A&P should be able to wire
the hot side of the clock to the hot side of the coil input of the Master
Solenoid, and the ground of the clock to the ground side of the master
switch, and the clock will stay on all the time...


Is the Master solenoid closer to the front of the panel than the Battery?

So why dis Piper wire it that way? Cessna has a separate circuit, the keep
alive circuit for what ever piece of equipment that needs it, that is wired
to the hot side of the master contactor. There is a fuse right next to the
master contactor for this circuit.



"Mark Mallory" wrote in message
...

Jay Honeck wrote:

Also, why is there a 7-second delay after turning the master switch on?

The 7-second delay is probably in your clock. That's how long the clock
continues to run after it's power is removed.


Here's how it works:

1. The clock is connected to the "hot" side of the master.

The "hot" side of the master does not go to the battery; rather, it goes
to the
COIL(-) of the master contactor. The battery goes to the *other* side
[coil(+)]

Your clock is thus not connected directly to the battery. The COIL of the
contactor is between the battery and the clock.


2. It works fine with master "off"

Yes, because it's receiving voltage *thru* the COIL (a resistance of
several
tens of ohms or so.) It works just fine.


3. Turn Master Switch "on" -- works fine for seven seconds.

The master switch connects the coil(-) to GROUND. The voltage at the
"hot" side
of the master (and the clock) goes to ZERO. Current flows from the
battery thru
the coil and switch to ground; causing the master contactor to close
(you'll
hear the "clunk" if you listen) and the airplane's electrical system is
energized.


4. At seven seconds, the clock goes out.

Because that's how long the clock runs after power is removed.


5. Turn Master Switch "off" and the clock comes back on.

Yes, the COIL is un-grounded, the contactor opens ("clunk") and the
electrical
system is de-energized. The voltage at the "hot" side of the master
returns,
and the clock runs again (unless it's wiped out by the inductive kick-back
from
the coil


What's going on? Why is this circuit set up to do this?

Ask the idiot (Certified Mechanic?) who wired in your clock that way!

"Jay Honeck" wrote in message news:ePArc.38163$gr.3760706@attbi_s52...
ASCII schematic:


Why is this circuit set up to do this?

If the long piece of wire from the solenoid to the master switch
should happen to short to ground anywhere, it would keep the solenoid
activated, instead of blowing fuses as it would if you were switching
the +12. It was the safest, most reliable design at a time when
today's clocks were unheard of.
--
Gene Seibel
Hangar 131 - http://pad39a.com/gene/plane.html
Because I fly, I envy no one.

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

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

Newps wrote:
: So why dis Piper wire it that way? Cessna has a separate circuit, the keep
: alive circuit for what ever piece of equipment that needs it, that is wired
: to the hot side of the master contactor. There is a fuse right next to the
: master contactor for this circuit.

I think Piper did it this way because the battery is in the tailcone, not
just on the other side of the firewall, and wiring the system like this
minimizes the potential damage if the "master contactor" wire should short
out.

As other have pointed out, Cessna airplanes have a small fuse right next to
the battery to run the clock and the hobbs meter (why the hobbs? so that
the renter can't fly around with the master "off" and run up no time!).
My airplane also has a small fuse next to the battery, that is wired up to
the white dome light so that I can have that light on with the master off.
I have an Astrotech clock that's powered by an internal 'AAA' battery, so
that's not wired up to anything.

--
Aaron Coolidge

$9 kitchen timer with velcro on the back. Big huge numbers. Loud alarm.
Homemade wooden wedge attached to panel of my Cherokee to fix it at a nice
viewable angle. Another strip of velcro on my knee board for when I fly
other planes. Works great. Less filling.



"Jay Honeck" wrote in message
news:wRurc.92436$iF6.8041834@attbi_s02...
Jay... I have a cheaper alternative.. I carry my "ships clock" on my
wrist..

Funny, that's what one of the wise old heads on the field said, while
Darryl
was poking around: "Why in HELL do you need an electric CLOCK, for
Chrissakes? Doncha got a WATCH?"

:-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Newps wrote:

So why dis Piper wire it that way?

Well, if you re-read Jay's original post, you'll see that Piper didn't wire the clock
that way. Jay's mechanic did. Jay's A&P could hook things up the way keep-alives are
wired on my Maule and my old 150, but that would require running the wire through the
firewall to the starter solenoid. Some A&Ps are reluctant to run new wiring through
the firewall.

So. Jay. Your mech is reluctant to run a wire all the way back to the battery.
Where's this master solenoid? That will be hooked directly to the battery. Maybe it's
convenient to hook up to that.

George Patterson
I childproofed my house, but they *still* get in.