Of clocks and learning curves...

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

ASCII schematic:

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

Thanks, Aaron.

For us electrical dimwits, can you explain the purpose of this circuit?

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

Here's how it works:

1. The clock is connected to the "hot" side of the master.
2. It works fine with master "off"
3. Turn Master Switch "on" -- works fine for seven seconds.
4. At seven seconds, the clock goes out.
5. Turn Master Switch "off" and the clock comes back on.

What's going on? Why is this circuit set up to do this?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

On Sat, 22 May 2004 04:38:34 GMT, "Jay Honeck"
wrote:

ASCII schematic:

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

Thanks, Aaron.

For us electrical dimwits, can you explain the purpose of this circuit?

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

Here's how it works:

1. The clock is connected to the "hot" side of the master.
2. It works fine with master "off"
3. Turn Master Switch "on" -- works fine for seven seconds.
4. At seven seconds, the clock goes out.
5. Turn Master Switch "off" and the clock comes back on.

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


I think this is whats going on Jay,
First, Aaron is right..the master switch is just a ground path for the
master solenoid.
The master solenoid has 12 volts going to it but dosen't work untill
the master switch is ON ..providing a ground path for it.
So with the master OFF, one side of the switch is at 12 volts (the 12
volts going thru the solenoid coil, and the other side is at ground.
Your clock must be hooked up to the hot side of the master switch, and
gets 12 volts thru the solenoid coil.
When you throw the master ON, BOTH sides of the master switch are now
at ground..and the master is now supplying a ground path to the
solenoid coil. Your clock power feed is now at ground and it croaks.
Why the 7 sec. delay?.... I bet you will find if you provide 12v to
the clock thru any source, then kill it..it will last for 7
sec..probably some capacitance built into the clock power circuits.

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!

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!

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

"Aaron Coolidge" wrote in message
...

I think Piper did it this way because the battery is in the tailcone, not
just on the other side of the firewall,

Many Cessna's, including my 182, have the battery behind the baggage
compartment.


As other have pointed out, Cessna airplanes have a small fuse right next
to
the battery to run the clock and the hobbs meter

I found this out the hard way. I had a leak in the rear window. It rained
and the water ran down and onto the master contactor, shorting it out and
turning it on, rendering the master switch on the panel useless. I learned
from this that my battery will run the turn coordinator and some instrument
lights for about 19 hours before it goes dead.

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.

The master solenoid is right next to the battery box. Running that extra wire is a pain
in a PA-28, it involves pulling off the left interior sidewall. Piper didn't put it in
there originally because the airplane did not have anything outside of the battery box
that needed always on power (the clock was a mechanical clock).

"G.R. Patterson III" wrote:

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.

--
--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

"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.