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Ground Power Z-31

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user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Tue Aug 09, 2022 5:33 am Post subject: Ground Power Z-31

Looking at Z-31, once the ground power relay is energized, its relay coil will

remain energized, being back fed from the aircraft battery via the ground 

power relay contacts.  It will be up to the pilot to open the circuit provided 

that he knows enough to do that and remembers.  But if he can't remember 

to shut off the master switch, he won't remember to open the ground power 

relay circuit either.  One solution is to put a limit switch in series with the 

ground power relay coil.  The limit switch could be operated by the cover of 

the piper style receptacle.

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Joe Gores

nuckolls.bob(at)aeroelect
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Posted: Wed Aug 10, 2022 1:36 pm Post subject: Ground Power Z-31

At 08:33 AM 8/9/2022, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 Looking at Z-31, once the ground power relay is energized, its relay coil will

 remain energized, being back fed from the aircraft battery via the ground 

 power relay contacts.  It will be up to the pilot to open the circuit provided 

 that he knows enough to do that and remembers.  But if he can't remember 

 to shut off the master switch, he won't remember to open the ground power 

 relay circuit either.  One solution is to put a limit switch in series with the 

 ground power relay coil.  The limit switch could be operated by the cover of 

 the piper style receptacle. 	


   Yeah, that's a down-side of the simpler, less expensive

   Cole-Hersee external power connector. We had some

   discussions about that back in the dark ages. The

   simplest thing to do would be to add a "GND PWR"

   annunciator light across the contactor coil that

   illuminates any time it's energized.



   We also did some brainstorming on a circuit to put

   in series with the contactor coil at the switch

   to detect when it had current flowing in it . . .

   this would also illuminate an annunciator. Sticky

   part was that what ever technology we used, it had

   to stand off the fault currents of crowbaring 

   a breaker open.



   That was a long time ago . . . I'll see if I can

   dig up the notes. One simple hack would be to fabricate

   a current operated relay that would close at anything

   above about 0.5A. Use this to light the annunciator.

   This would be the easiest thing to incorporate that

   would require a MINIMUM of added wires and nothing

   going thru the firewall.  The current relay could

   be fabricated with a coil of wire around a reed

   switch capsule. This device would easily stand off

   the crowbar trip current.



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

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user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Wed Aug 10, 2022 4:42 pm Post subject: Re: Ground Power Z-31

I don't know if a reverse voltage or reverse current sensor is available at a reasonable price.

If so, the sensor could monitor the current or voltage drop on the cable that goes between the ground power contactor

and aircraft battery contactor and  could open the ground-power contactor coil circuit when current is reversed.

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Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Thu Aug 11, 2022 10:11 am Post subject: Re: Ground Power Z-31

PIPER TYPE GROUND POWER SOCKET Aircraft Spruce Part# 11-00500 MFR

Model# 11041 is described as Diecast housing, spring-loaded door.

Assuming that the door is aluminum (non magnetic), a bar magnet could be 

epoxied to it.  Then a magnetic reed switch could be mounted out of sight, 

but within the magnetic field.  The switch should close when the door is 

open, thus enabling the aux contactor coil circuit.

 Another option is to use a microswitch to monitor the door position.

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