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Wiring for Ground Power

rockitdoc

Well Known Member
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I would like to wire my bird so ground power can be used to learn/troubleshoot avionics. I have installed a plug with a 30a breaker on the sub panel so ground power can be easily connected/disconnected. Currently, this wiring is simply attached to the pos and neg terminals of the battery with the 30a breaker in series between the pos bat terminal and the plug on the subpanel. Would it be advisable to disconnect the ship battery from this setup while running on ground power?
 
Ground power

I did my ground power differently. I wired it in to the fuse box after the master contactor. And i used an AC diode bridge and a fuse to avoid blowing up the electronics if power is applied backwards.

By wiring it after the master contactor, the master is left off when on ground power; the battery is not affected. By using the diode bridge, I cannot apply the voltage backwards and blow up the expensive boxes, but it takes 2 more volts on the power supply to get 12.5V to the plane.
 
The short answer is no.

The longer answer is depenent on how depleted your battery is - as in will it draw down your power supply output to the point where voltage is sagging too low.

Some thoughts:
- Do not run any electronics off of a battery charger, even if it is connected with the battery on line. The battery will not filter out the trash that these things tend to put out.
- With a nice 30 amp power supply you can run all your panel and charge you battery at the same time - just like your alternator does. Here start off with the power supply output voltage turned down, perhaps 12vc or so and note output current. If not high, slowly increase the power supply output voltage as you note current - don’t turn up so fast that you exceed the power supply current output capacity. Stop when you get to your normal alternator voltage output - say 14.2vdc for Odyssey batteries.

My dual screen SkyView panel with all the stuff, including the power hog GTN-650, draws just 10-12 amps so there is plenty of power supply capacity left over for the battery if it is low.

Here is a nice power supply that will do everything you need.
https://www.dxengineering.com/parts/mfj-4230mv

Carl
 
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The short answer is no.

Here is a nice power supply that will do everything you need.
https://www.dxengineering.com/parts/mfj-4230mv

Carl

This is the unit I have at the hangar. So far it has done everything Carl has mentioned without fail. I just made some long leads and connected direct to battery. It acts as an alternator would so the battery see no difference from where the power is coming from. Small, compact and easy to use too.
 
The short answer is no.

The longer answer is depenent on how depleted your battery is - as in will it draw down your power supply output to the point where voltage is sagging too low.

Some thoughts:
Here start off with the power supply output voltage turned down, perhaps 12vc or so and note output current. If not high, slowly increase the power supply output voltage as you note current - don’t turn up so fast that you exceed the power supply current output capacity.

Here is a nice power supply that will do everything you need.
https://www.dxengineering.com/parts/mfj-4230mv

Carl

That is the unit I have.

OK. I will stick with my plan. Here is how it looks, to date:

The female plug on the sub panel fits a male with cable that goes to the dxengineering power supply that Carl mentioned.

Ground Power Panel Outlet.jpg

The black and red conductors go through firewall and connect to battery (+) and (-) (yellow arrows)

Ground Power Connection to Battery.jpg

Question:

If the dxengineering power supply is set to 14.2 volts, will this charge the battery? If not, how does one determine if charging is happening? Clearly, this builder needs to read Nuckolls 's book again.
 
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Yes, 14.2 volts will charge a lead battery like the PC680. I don't know about charging a lithium battery.
 
Unprotected wires entering the cabin directly from the battery is big no-no for me.
 
Unprotected wires entering the cabin directly from the battery is big no-no for me.
Hmm…..
Maybe put the plug to the ground power FWF?

Although, thete is a 30a breaker between the battery and the subpanel plug.
 
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In the event of smoke in the cockpit or an imminent forced landing, the pilot should have the ability to shut off all electrical power as close to the source(s) as practical. It is not desired to have arcs and sparks when fuel is leaking.
 
With a 30a breaker between the +12v battery and the quick disconnect plug on the sub panel I should be protected against unwanted grounding (sparks) in the cabin, right?

Ground Power Panel Outlet.jpg
 
Why plug the power supply inside the cockpit? Wire a plug to the battery terminals and secure it somewhere underneath the oil door. When you want ground power, open the oil door and plug in the ground power directly to the battery. Avoid that risk of wires shorting through the firewall.
 
Why plug the power supply inside the cockpit? Wire a plug to the battery terminals and secure it somewhere underneath the oil door. When you want ground power, open the oil door and plug in the ground power directly to the battery. Avoid that risk of wires shorting through the firewall.

This is the way I've seen it done. I used to have this myself, but removed it since my battery is very accessible with alligator clips via the oil door.
 
With a 30a breaker between the +12v battery and the quick disconnect plug on the sub panel I should be protected against unwanted grounding (sparks) in the cabin, right?

View attachment 23531

only if the breaker or fuse is close to the battery. Otherwise, the wires from the battery to the CB is unprotected from a short, and in this case shutting off the master won't stop the smoke. It is inevitable that you will have some length of unprotected wire from the Batt or alternator to the CB's, but the goal is to minimize this and to keep it out of the cabin when possible. For your application, get an inline ATC fuse holder and put that where this circuit joins the battery. Can also make a small fusible link (4 AWG sizes down from the supply wire size).

Larry
 
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only if the breaker or fuse is close to the battery. Otherwise, the wires from the battery to the CB is unprotected from a short, and in this case shutting off the master won't stop the smoke. It is inevitable that you will have some length of unprotected wire from the Batt or alternator to the CB's, but the goal is to minimize this and to keep it out of the cabin when possible. For your application, get an inline ATC fuse holder and put that where this circuit joins the battery. Can also make a small fusible link (4 AWG sizes down from the supply wire size).

Larry

Excellent explanation. Thanks. After thinking about this based on all the feedback, the way I had it fabbed could have been problematic. An in-line fuse next to battery is the solution. Here’s what I intend to use:

https://bandc.com/product/bolt-down-fuse-base-with-cover/

https://bandc.com/product/midi-bolt-down-fuse-23a-through-70a/


Small, robust, neat.

I will mount it on the battery box so no added holes in firewall.
 
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Bad or incorrect power supply fried panel

Interesting and costly story. Make sure you test your power supply before first plug in on your panel.

I built the full size mock up for the B 2 bomber for the movie Broken Arrow. It had to be built in 3 parts to transport from Long Beach airport to the studio. Another company did all the avionics. One day, the panel was switched on for the first time. Lots of smoke and bad words. Somehow the transformer or power supply was broken or incorrectly set, but everything plugged in on the cockpit was toast. I was really glad my part was just the underside with stairs going into the cockpit and the structure of the cockpit and rough supports for the panel and switches.

I had built boats before and we did the plane just like a boat. Ribs and strips of plywood so we could get the compound angles correct. We were using cement trowels to spread bondo after we glassed everything. Lucky weight wasnt a problem. I bet it weighed more than the real plane. It was an interesting project. I only got the job because a friend was one of the helicopter pilots and they were desperate!
 
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