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,<snip>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
Vern,
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.
I have the exact same set-up. I keep a batter maintainer plugged into the "hot" plug when in the hangar.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
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.