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Hints for Homebuilders: Alternate Power Supply - safety question/suggestion

Posted By:
Josh Berman
#1 Posted: 6/24/2011 07:10:46

I enjoyed Jack's Hints for Homebuilders video on the Alternate Power Supply (http://www.eaavideo.org/video.aspx?v=1009394733001 ). It seems like a good idea to have an accessible way to recharge your plane's battery.

However I'm concerned that while his method of repurposing a standard extension cord for this is quick and inexpensive, it allows the possibility that either the end wired to the plane battery OR the free end used to attach to the "charging" battery could inadvertently be connected to live 120VAC, with potentially dire consequences.

To protect against this happening, I'm wondering if it would it work to instead use the "ground" and "neutral" pins/wires with the following cable modifications?

  1. On the cable to be attached to the "charging" battery, snip-off the "hot" (ie: smaller) blade flush with the end of the plug, then cover the snipped-off blade with a permanent, insulating material, so that only the "ground" (round) and "neutral" (larger) blades remain.
  2. Paint the plug-end a contrasting color, and/or label it as "AIRCRAFT USE ONLY"
  3. On the cable attached to the airplane battery, block the "hot" (ie: smaller") blade slot by filling it with epoxy, hot-melt glue or some other permanent, insulating material.

In this way, if someone attempts to plug a normal extension cord into the airplane, it physically won't fit, so 120VAC can't be connected to the 12VDC aircraft battery.

Also if someone tries to plug the "charging" cable stub (with exposed battery clips) into a 120VAC outlet, hopefully the contrasting color/label AND missing "hot" blade will discourage them from actually plugging it in. But if they do plug the cable into an 120VAC outlet, you're only dealing with exposed "neutral" and "ground" attached to the outlet, not "neutral" and "hot".

You could take this one step further and physically modify the plug-ends by adding material (epoxy, etc...) to the male plug around the snipped-off "hot" blade (and making a matching relief on the aircraft-attached "female" plug) so that the male plug physically won't fit into a 120VAC outlet, but I think that's quite a bit more work.

OR, simply get a "battery tender" type cable (such as:  http://www.amazon.com/Battery-Tender-081-0069-6-Terminal-Disconnect/dp/B000NCOKZQ/  or see attached picture)  to connect to your aircraft battery, and make (or buy) another battery-tender plug cable with alligator-clips that you can keep in your plane JIC it needs a charge while you're away from home. The upside of this method is that not only do you eliminate the chance of 120VAC meeting 12VDC in a spectacular or dangerous way, but you can also use a battery tender to keep your battery topped-off while your plane's in the hangar.


 - Josh

Files Attachment(s):
battery tender plug.jpg (34687 bytes)
Don Norman
Homebuilder or Craftsman
#2 Posted: 7/1/2011 08:15:15

I used a very simple method that works great.  I have an  Odyssey battery on my RV6-A and an Odyssey battery tender .The battery is inside the cabin. The battery tender came with wires to a two post plug as the main connection to the battery.   I lengthened these wires, permanently  connected them to the battery and placed the plug under the instrument panel near the passenger side knee area. I simply ran it up a control cable and taped it into position. There it is easy to access from the wing.  I obtained a similar plug from an auto supply store, cut off and taped over the wires on the matching plug and used it to cover the otherwise exposed live plug plug post while the tender is not being used.  To use, I simply put the tender on the wing walk area plug in both the battery and the AC and turn it on.  Two minutes, no sweat.

Don Norman