Van's Air Force
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Ground power plug
- Thread starter rwayne
- Start date
w1curtis
Well Known Member
Same place as on my Cardinal--rear by the battery but rather that on the external side, I'll put it on the external bottom with a spring loaded door to an AN-2552 receptacle.
AN-2552 Receptacle
http://nerv10.com/wcurtis/90Electrical/RV10WireBookPage2.pdf
AN-2552 Receptacle
http://nerv10.com/wcurtis/90Electrical/RV10WireBookPage2.pdf
Last edited:
vlittle
Well Known Member
I've reviewed Bob Nuckoll's aeroelectric design for ground power, and found a couple of opportunities for improvement.
Bob's design uses the Piper style jack rather than the three-wire MilSpec jack. In my opinion, this is not good. Once energized, his design will stay ON even if the ground power is disconnected. This leaves the Jack live and drains the main battery due to the ground power contactor load.
The problem scenario is if you have a line-person charging your battery with a GPU. He/She is likely to disconnect the GPU when you are not there. You come back a day later and your battery will be dead. Sort of defeats one of the purposes of a ground power connection.
Secondly, I see a scenario where you may want to provide a boost to another aircraft from your own. Bob's design does not let you turn on the ground power jack unless there is external power. Small problem maybe, but there's an easy way to get around this. [Note, for this to work, there must also be one of the special jumper plugs inserted that allows booster cables to be used].
To fix these deficiencies, use the 3-wire Milspec jack that provides an external contactor power lead. In addition, add a extra diode and momentary contact switch to allow you to turn on the ground power jack from your internal battery.
With either internal or external control, disconnecting the external power plug will shut off all load on the battery and de-energize the jack.
Since a picture is worth a thousand words, here's a sketch of my design for a HRII:
The GPVolts signal goes to a voltmeter that has a momentary contact switch to select between main bus and ground power measurement.
One more comment: William Curtis's design does not connect directly to the main battery. This prevents the ground power from charging the main battery if it is dead. The main contactor cannot be turned on to allow charging.
Vern
Bob's design uses the Piper style jack rather than the three-wire MilSpec jack. In my opinion, this is not good. Once energized, his design will stay ON even if the ground power is disconnected. This leaves the Jack live and drains the main battery due to the ground power contactor load.
The problem scenario is if you have a line-person charging your battery with a GPU. He/She is likely to disconnect the GPU when you are not there. You come back a day later and your battery will be dead. Sort of defeats one of the purposes of a ground power connection.
Secondly, I see a scenario where you may want to provide a boost to another aircraft from your own. Bob's design does not let you turn on the ground power jack unless there is external power. Small problem maybe, but there's an easy way to get around this. [Note, for this to work, there must also be one of the special jumper plugs inserted that allows booster cables to be used].
To fix these deficiencies, use the 3-wire Milspec jack that provides an external contactor power lead. In addition, add a extra diode and momentary contact switch to allow you to turn on the ground power jack from your internal battery.
With either internal or external control, disconnecting the external power plug will shut off all load on the battery and de-energize the jack.
Since a picture is worth a thousand words, here's a sketch of my design for a HRII:
The GPVolts signal goes to a voltmeter that has a momentary contact switch to select between main bus and ground power measurement.
One more comment: William Curtis's design does not connect directly to the main battery. This prevents the ground power from charging the main battery if it is dead. The main contactor cannot be turned on to allow charging.
Vern
APU Jack
Vern,
Why couldn't you use a Marine grade manual battery switch that is commonly used in larger craft with dual batteries? I have that type set up in my boat using two batteries and an external receptical since the batteries and terminals are in enclosed watertite boxes which are a PITA to open and close up(location beneath deck in engine compartment). I have never had a problem with the set up and it is standard wiring in Chris Craft, Sea Ray, etc. The switch is directly wired to the batteries with 0/4 wire and it has a manual selector built into it.http://cgi.ebay.com/ebaymotors/Boat....c0.m245&_trkparms=72:543|65:12|39:1|240:1318
Mike H 9A/8A
Vern,
Why couldn't you use a Marine grade manual battery switch that is commonly used in larger craft with dual batteries? I have that type set up in my boat using two batteries and an external receptical since the batteries and terminals are in enclosed watertite boxes which are a PITA to open and close up(location beneath deck in engine compartment). I have never had a problem with the set up and it is standard wiring in Chris Craft, Sea Ray, etc. The switch is directly wired to the batteries with 0/4 wire and it has a manual selector built into it.http://cgi.ebay.com/ebaymotors/Boat....c0.m245&_trkparms=72:543|65:12|39:1|240:1318
Mike H 9A/8A
vlittle
Well Known Member
Hi Mike. I did look at this extensively but decided on the electrical contactor approach for a few reasons.
I like the idea of manual switches, but they should be located close to the battery to prevent long runs of unprotected always live wires. In my HRII, I've moved my battery back 3 feet to well behind the baggage compartment, which means that the ground power switch and jack would be mounted in an inacessible area, or behind a hatch on the external skin near the battery.
Given that the weight is comparable to a contactor, I decide to use a contactor and mount the ground power jack in the interior, thus not punching additional holes in the fuselage. The contactor system also allows overvoltage protection
I may still end up with a manual battery switch buried inside to simplify main battery disconnect during maintenance. I'd still have to crawl back there to turn the switch, but it's easier than unbolting battery terminals.
If I had left the battery in the original location, I probably would have used a manual switch because it's simple and reliable.
Thanks, Vern
w1curtis
Well Known Member
Starting is primary
The PRIMARY purpose of ground power is starting NOT charging. You would not need such large current carrying ability if you are just charging your battery. At first, I wondered why Cessna wired it this way. After thinking about it a for a while, I think it makes sense. In my (Cessna) design, in order for the batter to be charged, you have to turn on the master switch.
The other thing that you have to worry about is voltage transients from the ground power device. This was one of the primary reasons Cessna separated it from the main bus via the master contactor. It allows you to be certain of the power before throwing the master and possible ruining your avionics.
If I was installing a system with a primary purpose of charging, I would not use the large conductor AN-2552, I would use a much smaller, simpler, cheaper, maybe a trailer hitch jack. I could also easily wire in another contactor that would charge the battery from the same plug without connecting the main buss, but this adds needless complexity IMHO.
Vern,
The PRIMARY purpose of ground power is starting NOT charging. You would not need such large current carrying ability if you are just charging your battery. At first, I wondered why Cessna wired it this way. After thinking about it a for a while, I think it makes sense. In my (Cessna) design, in order for the batter to be charged, you have to turn on the master switch.
The other thing that you have to worry about is voltage transients from the ground power device. This was one of the primary reasons Cessna separated it from the main bus via the master contactor. It allows you to be certain of the power before throwing the master and possible ruining your avionics.
If I was installing a system with a primary purpose of charging, I would not use the large conductor AN-2552, I would use a much smaller, simpler, cheaper, maybe a trailer hitch jack. I could also easily wire in another contactor that would charge the battery from the same plug without connecting the main buss, but this adds needless complexity IMHO.
L.Adamson
Well Known Member
I just use a 12V. cigarette type outlet under the right side panel. It's fused just past the battery and is always "hot". My battery charger is adapted for the male end. And this of course, would be for charging only, and not a high amperage jump.
Have another outlet on the left, that's through the regular master switch, as it operates my headphones.
L.Adamson --- RV6A
I have the exact same set-up. I keep a batter maintainer plugged into the "hot" plug when in the hangar.
vlittle
Well Known Member
Point taken that it's not primarily a charging jack. Nevertheless, my builder buddies us ground power quite extensively during construction to power avionics, and it's nice to have it automatically shut down when external power is removed, without remembering to turn off the GP switch.
Also, I think your schematic has a fundamental design limitation. You cannot turn on your master contactor at all with a dead battery. Therefore, even if you start the aircraft with ground power, you will have no electrical power when it's removed. I believe that ground power should connect directly to the battery bus without the master contactor in between. You would turn on ground power, then the master, start the engine, turn off the ground power and remove the external cable. Your battery will then be charged by the alternator system at that point.
Perhaps Cessna believes that if your battery is dead you shouldn't be starting your engine and using your (overstressed) alternator to charge it. This has some merit (you should charge the battery with a proper charger if it's dead).
I'll think about that one for a while, and maybe Bob Nuckolls has an opinion.
Thanks, Vern
