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Ground Power socket connect using battery isolator?

blaplante

Well Known Member
I have the Piper style 2 connection socket for ground power. Not wanting the socket to be battery hot all of the time I have a contactor and switch to engage the socket. But thinking about this I wonder why this couldn't be simplified by using a Schottky battery isolator (high power rectifier) that would only allow current from the ground power *to* the ship? these are available in 200A and more ratings and drop about 1/2 of a volt.

Something like this https://www.mouser.com/ProductDetai...MIvezq26eX4wIVlvhkCh3vTgJeEAQYASABEgJ0GPD_BwE

although that one is a dual unit, but you get the idea.

Thoughts?
 
Looking at the data sheet, the forward voltage drop will be more like 1 volt. I think that with a diode in the circuit, engine cranking will be degraded quite a bit. How about Bob Nuckolls' Z-31 ground power circuit? The socket is not hot unless the switch is turned on. Expensive avionics are protected against both reverse voltage and high voltage.
 
Should work fine, if you parallel the diodes. The 200 Amp rating for each diode is for 50% duty cycle, so both are needed.

Bear in mind that there can be a leakage current, up to 160 mA if you short the plug or leave a load on it. This may not be a concern since you will be charging, jump starting or using it to power avionics loads.

This a lot lighter, less complex and more reliable than a contacter/diode based system, but it will be intolerant of overloads.

Good luck.
 
Recommend you consider not using one of these 1960 clunky ground power plugs at all.

Your airplane is not a car and should not be treated as such. If you need to jump start your airplane, you have better options than this. I offer:
- A dead battery(s) is a scream out to you that it has been neglected or abused. While a jump start might get the engine running, you would have no idea how much your battery capacity has been degraded.
- If you abuse your battery (like leaving a master on) consider that battery dead and replace it. While you might be able to breathe some life into it the damage is done. These days new Odyssey batteries are available in stores across the nation.
- If you simply drained the battery while playing with the panel, then charge it back to full capacity before launching into the ether. Here a easy jumper to a nice light 30 amp power supply (not a battery charger) will keep the battery(s) topped off while you spend hours hangar flying. Such power supplies are around $90: https://www.dxengineering.com/parts...MI-4i90uuY4wIVW0wNCh0ZLwO0EAQYBCABEgLR7fD_BwE

Do not run your panel on a battery charger.

Carl
 
reply

Yes, I have a proper modern charger for the PC680 chemistry, and yes I don't use a battery charger to run my avionics.

Regarding the voltage drop, the curves show 1 volt only at around 1000A... at 100A the drop is 0.6 volts.

I had missed the largish reverse leakage current spec - good catch. But I agree for the purpose it is not much of an issue.

-Bryan (BSEE 1977)
 
Recommend you consider not using one of these 1960 clunky ground power plugs at all.

Your airplane is not a car and should not be treated as such. If you need to jump start your airplane, you have better options than this. I offer:
- A dead battery(s) is a scream out to you that it has been neglected or abused. While a jump start might get the engine running, you would have no idea how much your battery capacity has been degraded.
- If you abuse your battery (like leaving a master on) consider that battery dead and replace it. While you might be able to breathe some life into it the damage is done. These days new Odyssey batteries are available in stores across the nation.
- If you simply drained the battery while playing with the panel, then charge it back to full capacity before launching into the ether. Here a easy jumper to a nice light 30 amp power supply (not a battery charger) will keep the battery(s) topped off while you spend hours hangar flying. Such power supplies are around $90: https://www.dxengineering.com/parts...MI-4i90uuY4wIVW0wNCh0ZLwO0EAQYBCABEgLR7fD_BwE

Do not run your panel on a battery charger.

Carl

All of the above are good recommendations, and ones that I practice as written.
See schematics:

http://www.vx-aviation.com/sprocket/photos/panel_elec/schematics-2/MASTER.pdf

http://www.vx-aviation.com/sprocket/photos/panel_elec/schematics-2/ELEC.pdf

But when you are stuck on the ground in Lower Upchuck it sure would be nice to jumpstart the aircraft to get to a real airport for servicing.

I had a battery failure and managed to charge it through my always hot 12V accessory plug (second link above). The mechanic who provided the charger stayed late to help me out... at no charge.

But for those who choose a GPU plug, the diode looks like it will work.
 
If you want to roll your own, those connectors are used as charge connectors on electric fork lifts, and I think I've seen them on electric golf carts, as well.

If the goal is primarily emergency 'jump start', planes with a firewall mounted battery can use a simple 'hot' post located where it's accessible through the cooling exit. Cap it with an insulating boot that can be removed or pushed out of the way for the jumper cable. Exhaust pipes or an engine mount bolt for ground.

FWIW, any of the options discussed do leave you vulnerable to potential overvoltage, if a careless line person hooks you up to the 24V (or jet) start cart. The contactor detailed in AEC has OV protection.
 
Hot Post?

Maybe I'm a nervous one, but a (always?) 'hot post' down the the lower cowl make me concerned. Why? Take an off airport landing... high probability of ripping the gear off, and now the hot post is banged into the firewall. Lots of sparks. And in that landing there's probably a ruptured tank...

Maybe because I saw I guy short out a car battery and had the battery literally blow up in his face that I'm nervous about shorts.

Seems like another place to use an isolator or relay so it isn't hot always.
 
Good point. I've got a 'hot post' in my -4, but it's accessible through the oil door. I never intend to use it for jump starting; only for charging the battery. Obviously not as safe as nothing at all, but pretty close. The battery sits on the footwell shelf, so the wire is about a foot long, and above a top motor mount tube.

The only reason I mentioned making it accessible in at least a marginally safe area for jump starting.
 
Regarding ground power socket

If your purpose is to be able to jumpstart your plane why not use an EarthX jumpstart pack. You can run the EarthX accessory wire/cable, purchased separately, from the battery and inside the cockpit in order to jumpstart the engine conveniently and by yourself. The cable is not the same as the one you use for a battery charger.
 
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