---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 08/12/22: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:33 AM - Re: Ground power (GLEN MATEJCEK) 2. 06:48 AM - Re: Ground power (user9253) 3. 11:40 AM - Re: Re: Ground power (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 04:33:04 AM PST US From: GLEN MATEJCEK Subject: AeroElectric-List: RE: Ground power > Hi Bob- > > > With regard to the indicator LED, my intention was that the polarity > indicator, and especially the reverse polarity indication, be functional > regardless of the breaker condition. The choice of a bidirectional LED > for the indicator was due to simplicity and the fact I've got a stack of > them on hand. It would be a minor thing to go to discrete indicators. > As to the reverse polarity diode in the contactor ground line, my thoughts > are that the spike catching diode on the coil wouldn't be long for this > world if reverse polarity external power were applied across it, and then > the contactor would close. > Thoughts? > ________________________________ Message 2 _____________________________________ Time: 06:48:43 AM PST US Subject: AeroElectric-List: Re: Ground power From: "user9253" I like your circuit. It will not pop the breaker in case the aux power polarity is reversed. Nothing will happen except that the red light will come on. But the circuit does not solve the problem of the contactor remaining energized until the aircraft battery is depleted, that is if the pilot does not shut off the aux power switch. Ideally the aux contactor would drop out when the aux power plug is removed. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=507659#507659 ________________________________ Message 3 _____________________________________ Time: 11:40:07 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Ground power At 08:48 AM 8/12/2022, you wrote: > >I like your circuit. It will not pop the breaker in case the aux >power polarity is >reversed. Nothing will happen except that the red light will come on. The catch diode across the coil takes care of that. It prevents the contactor from responding to reverse power while presenting a 'fault' current to the breaker/switch. > Nothing will happen except that the red light will come on. >But the circuit does not solve the problem of the contactor remaining >energized until the aircraft battery is depleted, that is if the >pilot does not >shut off the aux power switch. That's what the annunciator is for . . . the light should be illuminated only when ground power is being used. If the contactor is 'latched' due to pilot inattention to ground power controls, then the light will serve as a reminder that the switch is not properly positioned. >Ideally the aux contactor would drop out >when the aux power plug is removed. That's ONE of the reasons that the third 'pilot pin' was added to the commercial/military version of ground power receptacles. The pin is shorter thus preventing arcing at the ground power plug pins during mate/demate in addition to de-energizing the ground power contactor any time the power cart is not plugged in. Incorporation of the Cole-Hersee, ground vehicle power connector was a compromise in favor of much lower, simpler cost. Recall also that many installations of the C-H connector on aircraft did not include a pilot operated ground power contator (as explained in my article of some years back). The contactor center pin was simply hardwired to the ships bus structure. This is lead to an incident I cited when departing Kansas City on a very cold morning. The ground power operator had his back turned to me while dumping 28v into my 14v airplane. Lack of pilot control opened a door for the ov event I experienced. It also made for erosion of the center pin on FBO ground power cables AND customer ground power jacks when the connector was mated/demated under load. That incident prompted the article back in '97. Here's a clip of the suggested wiring. Note steering/clamp diodes that will deal with reverse polarity. OV crowbar for the high voltage issue. Annunciator that speaks to (1) availability of power at the connector and (2) mis-positioned switch after ground power is disconnected. The annunciator press-to-test feature added a way to see if ground power was indeed available before closing the ground power switch. Finally, adding the contactor and switch put the whole situation under the pilot's control. Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.