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PA-12 Battery Mystery

G

GossSHOP

Registered User
Hello! We are currently working on a project to finish putting together a PA-12 that was untouched in storage for a couple of years. I do not know the full details, but this is an aircraft that was worked on at another location. So far, it has been pretty straightforward. However, we've run into a bit of a hitch with the battery location. The original battery box has been provided, and the intent is to use it. However, the cables for the battery have been routed into the Aux Luggage Compartment. To clarify, it is not the underside, but straight into the Luggage Compartment, through the AFT wall of the compartment. There is no structure or brackets inside of this compartment that would indicate a place for a battery or battery box to sit, and the floor panels for the Luggage Compartment do not show any openings or hardware attachment point either. Looking through the documents that came over with the aircraft, we have not come across any STC or 337 that provides a clue for the battery location or why the cables were routed as such.

Has anyone on this forum come across this before? Or perhaps know of an STC that applies to this change in battery location? I have included these two pictures for referance.

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I'm a wire Nazi, but you need to run new cable. If you are going to leave the battery aft, in the stock location, route the cable low just like the originals did. You will not need an STC or field approval just route or re route electrical wires. If you have reason to worry about chafing, sleeve the cable as needed with some kind of anti chafe sleeve or tape.

In the first pic, I'm assuming the multiple, large gauge wires coming forward from the grommet on the panel are your starter cable and two bus feed wires. Is that correct? If so, what are the large cables directly below them with the blue tape?

For safety reasons, I always recommend installing a master relay on the battery box. This allows you to install a start relay somewhere forward (I like the aft side of the firewall) and also use a short run of 12 gauge for a main bus feed. If you ever have an electrical problem such as a stuck start relay, you can stop it by switching off the master relay instead of sitting there hoping the starter won't catch fire before the battery goes dead.

Web
 
Thank for the reply wireweinie! And gary is correct.

The large cable below in the first picture, the one with the blue tape, is the same wire bundle. When we received the frame, the cables were already through the grommet but not tied together. Just kind of all over the place. So I taped them together for the time being to have some semblance of order and to not have to fight them everytime we had to do work in there.

As for rerouting the wires to the stock location of the battery, there are a few issues with that. The first is that all the wiring was already completed by whomever worked on this aircraft before it went into storage. Minus the battery relay and the battery location, of course. The wires for the battery were routed through a conduit along the belly of the fuselage, all the way towards the back to maybe a foot forward of where the grommet is. It then comes out and is clamped to the airframe structure, travelling up along the right hand side, before being passed through that grommet in the back. Rerouting would be possible, but not ideal as we then run into the second issue.

The airframe is new. It is a PA-12 frame, but it is a new build frame. We have no brackets or structure in place to indicate where the original battery box stock location is, or rather, was. And, having seen the other forum thread that Gary shared, I can say with certainty that the original battery stock location is no longer an option. That area behind the rear seat, which I am to understand was originally the luggage compartment where the battery stock location was, has been modified to be a sleeping area. And, as for the area beneath the rear seat, that space has been taken up by the VLT, electrical buses, and the power supply box for the strobes.

Honestly, the only indication we have of where the battery was intended to go, is where the cables are currently. And, as the airframe has already been fabric covered, we do not have many areas for us to attach a clamp to, let alone weld a bracket or anything of the such.

We'd like to assume there was some sort of plan in place for the battery location, before the airframe went into storage. And that it wasn't just someone going cowboy on this, which is looking more and more like that's what happened. But, benefit of the doubt and all that. There was not STC with the documents sent over with the airframe that shows this battery modification, which is why we are looking to see if there is some STC or such out there that someone knew about :-?
 
Mount an Odyssey battery under the pilots seat, and save a bunch of cable, complexity and some weight. You’ll move the CG forward, but put survival gear in aft baggage
 
If you are not going to install the box in the stock location, your only other choice is to install the box somewhere else. Build a shelf that will support the weight safely and use steel adel clamps to install it. You'll need to work with your IA to make sure he's happy with the structure.

It sounds like your wiring might be in the stock location under the floor. If so, and you have enough length, you can connect those cables/wires to the battery and relay. *BUT* I still stress that the stock wiring system is not that safe and updating it now will save you a LOT of trouble. For example, the stock wire system will have a large cable (2 ga) that connects to the start relay, two 10 ga wires that connect to the stock DPDT master switch, and an 18 gauge wire to operate the start relay. And you are correct if you point out that there is NO master relay in this system.

If you update to a modern system (think PA-28 or Cessna 185) a master relay will mount onto the side of the existing battery box. A single 4 ga cable will route from the master relay to the start relay on the back of the firewall. Then a single 20 gauge wire will route to the master relay to operate it. Use a single 12 ga wire from the hot side of the start relay to power your bus and you're done.

There is a shortcut if you wish to use it: leave one run of the heavy cable in place (if large enough, 4 ga or 2 ga) then all you have to do is remove the rest of the wires and push through a 20 gauge wire for the master relay operation.

Stop being intimidated by wiring. It's just a hydraulic system for electrons.

Web
 
I have a field approval I'd be glad to share with you putting an Oddesey battery under the rear seat, lots of room there and easy enough to do.

I would not move it under the front seat considering most 12s don't need and more forward CG and its crowded there if you have original gear. PM me if you want copies of my 337 field approval data and pictures
 
I moved mine from the stock location to under the rear seat. Made a shelf out of aluminum and affixed a battery box for an Odyssey. Master relay, starter relay and bus bar between. Easy clean install. All new wires. Turned out great.
 
Guys, from his previous message: "And, as for the area beneath the rear seat, that space has been taken up by the VLT, electrical buses, and the power supply box for the strobes."

That said, I'm not sure what a "VLT" is, but seems to me that an Odyssey battery would fit even with other stuff, that's a pretty wide seat.

MTV
 
Thank you for all the replies and suggestions folks!

As has been pointed out, unfortunately the underside of the rear seat is not a viable option as other stuff has been placed there. And, I meant to type "ELT" and not "VLT", small little typo on my end. Also, yeah, the front area is pretty clustered as is, so that is not really a good choice for this.

For the time being, the option to build a new shelf in the aux luggage may end up being what we go with.

But again, thank you all for the suggestions and replies!
 
If you are not already aware keep in mind that you can use a small light battery in the baggage area if you wanted to. The 12 type certificate only says "12 volt" for the battery. Doesn't list any other specific .
 
GossSHOP said:
Thank you for all the replies and suggestions folks!

As has been pointed out, unfortunately the underside of the rear seat is not a viable option as other stuff has been placed there. And, I meant to type "ELT" and not "VLT", small little typo on my end. Also, yeah, the front area is pretty clustered as is, so that is not really a good choice for this.

For the time being, the option to build a new shelf in the aux luggage may end up being what we go with.

But again, thank you all for the suggestions and replies!
Click to expand...

Are you familiar with the Odyysey batteries, and other compact batteries? If not, their size may surprise you.

MTV
 
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