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Ground Power Wiring

B

Bill Cannon

Member
Hello All,

After not building for a few months I am able to put in a couple days and am getting back up to speed. I have a wiring diagram from someone I trust that has the ground power receptacle wired between the Master Relay and the Starter Solenoid. To do this in the 10 (with battery in rear and ground power plug in rear as well) I would have to either run two #2 wires aft to front or join them at the master relay lug. The problem is the lug isn't long enough for two terminals. The nut that is on the relay lug up against the insulator is thick and doesn't leave much room.

Questions....

1. Why not run the ground power right to the + battery terminal? I don't have a battery yet but I am assuming I can get another #2 terminal attached to it. This, it seems, would solve my issue. Is there any advantage/downside/major issue to having it connected upstream or downstream of the Master?

2. In order to get two terminals on the Master Relay I would have to grind down the nut that is up against the insulator. It doesn't seem like this nut needs to be that thick. It is a specialty nut with a swiveling flange that I have not been able to find in a lower profile.

I've been scratching my head over this for a while and don't want to over think it. I already have though..... thought about building a copper buss bar but that will add time and weight.

Any thoughts or suggestions appreciated,

Bill Cannon
 
First, what is this for? If you hope to jump start the engine then you need heavy cables. But if it is just for running avionics on the ground, or a charger, you don't need #2 wire.
Attaching after the master means that if your main battery is so dead that it cannot power the master relay, then even if you jump start the engine the master still won't operate. And you don't want to run the alternator without a battery in the circuit.
Attaching directly to the main battery means a very heavy current draw if it's completely discharged. Also, the connector would always be 'hot' - an accident waiting to happen anytime you are working around the connector area.
What I am saying is this is not as simple as you hoped. Personally, I put in a small (#12) wire with an inline 20 amp fuse, directly to the battery, for charging only. If I leave the master on I'm resigned to waiting 3 or more hours while the battery gts charged back up.
 
I agree with Bob. If you are looking for a simple charging connection, do as he describes. If you want a more robust jump start connection, look at Bob Nuckolls method on the Matronics AeroElectric list. I have both in my -10, and they coexist nicely.

Jim Berry
RV-10
 
I have a relay for the ground power too. To clarify it would be the 2 gauge coming off the ground power relay that I would be either attaching before or after the master relay. My understanding is that the plug wouldn't be hot unless the relay closed by having the ground power plugged in and on (three pin receptacle) thus energizing the relay. Of course the wire to the relay would be hot if attached directly to battery but it is tough to reach when trying so I'm not too concerned about that. I have the plug mounted just aft of the baggage bulkhead with access via the bag door and a yet to be made door in the bulkhead.

I would like to be able to jump start it if need be and already have 2 gauge going from the receptacle pins to the ground power relay and ground. The plug is less than 2 feet from the battery so the wires are short but I didn't even think of using smaller gauge. I was thinking I needed 2 gauge for starting with a dead battery. With one terminal mounted on the relay there is only one or two threads showing when all nutted on so I doubt using a somewhat smaller gauge would allow me to mount a second terminal to the relay.

If the battery were dead and the ground power was connected via it's own relay to the battery, would the ground power be able to energize the master relay in order to start the engine? Maybe that's why the wiring diagram that I have has the ground power going directly to the starter solenoid.

I don't know if this clarifies or muddies the picture but thanks for the advice so far.

Electrically ignorant,

Bill
 
I forgot about those diagrams in AeroElectric that you referred to. I see what I am looking for. He has the ground power attached prior to master relay with two wires going to the master relay. That presents the same problem since the relay can't handle two wires on either side. I see no difference in running it to the battery and from the battery to the relay.

Thanks for the help,

Bill
 
I have put quite a few ground power jacks next to the battery, either in the belly or the rear baggage wall. I run it to the battery side of the master solenoid or to the battery terminal itself. I use the Piper Style Plug that Spruce sells. Then I make a "dongle" with a 6" piece of #2 wire into a Piper pkugnthatnfits into the jack and I keep that in the baggage area. If I want to out a trickle charge on the battery, I plug in the dongle and hook the red to the end of the wire and the black to the ear of the plug. If I want to work on the panel without drainingmthe battery, I do the same with a higher amp charger. If I need a jump, I hook jumper cables up to a car the same way and it fires right up. That is why I prefer it on the outside of the plane. I don't see it as dangerous at all. The plug style keeps it safe. Also, if you out it on the bus side of the master solenoid, you have to have the master switch on to charge, which would likely power other bus items, requiring a higher charge rate and having your master switch on the whole time. I don't like that idea. Also, as was mentioned, that could damage stuff if you hook a charger up and don't have the master on, so no battery in the loop.
 
I don't know why you say your master relay can't handle two lugs on one side; every contactor I've seen can easily take two terminal lugs for #2 AWG wire. I'm using the Vertical Power diagram for a ground power receptacle and you can see my unfinished installation below. The master contactor is the farther one; the ground power contactor is the near one. On the near terminal of the master contactor is the jumper from the ground power contactor and also the line from the battery.

FP22062013A0003U.jpg
 
I can get a different contactor if need be. The one that Vans sold me will not take two. Between the two nuts and the lock washer I barely have one, maybe two threads showing with just one terminal on it. With two terminals the outer nut hangs off by a thread. I'm toying with running it straight to the battery terminal and if not i'll get a different product.

Thanks all,

Bill
 
If you can get the nut on all the threads (but none showing) I wouldn't worry about it with the lockwasher.
OR How about deleting the lock washer and using a low-profile, all metal lock nut?
 
Or possibly find a low-profile backing nut. Anyway, I seem to recall using a Vans-supplied contactor for the RV-6A but these are from Aircraft Spruce because I'm doing a 28V system. The 14V version is part number 11-03161 and costs $25.
 
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