Alternator Wire Breakage

[Bob Axsom]

When I had 55.3 hours on our RV-6A the Alternator wire broke between the end of the wire insulation and the heavy terminal. I thought about the configuration and it seemed like the flexing had to be concentrated in that small space. My solution was to bridge the gap with a couple of lengths of black shink fit sleeving. On the 5th of February we were about 20 minutes out of St. Augustine, FL the low voltage light came on. This was at 170 hrs or about 120 hrs after the first failure. The circuit had opened again but this time the tongue of the terminal had broken off at the barrel just forward of the sleeving. It was a bit of a hassle but I pulled the cowling and a maintenance shop by the Galaxy FBO reterminated the wire. Friday we flew to Panama City to visit friends. This morning (2-13-06) we headed for home in Fayetteville, Arkansas. I climbed to 6,500 and was faced with a 35 kt headwind so back down to 2,500 ft where the ground speed came up to 167 to 172 kts. Staying out of the Restricted Areas, etc. in that area requires some zigzaging (time wasting) but as soon as I cleared them to the north I turned toward Meridian, Mississippi and as I crossed that city the Low Voltage warning light came on again. Having a LASAR ignition system I knew if I shut down to refuel with a dead battery I could not restart the engine so I shut down the avionics and really started managing the fuel. I dug the sweetest little machine ever made (Garmin GPS 90) out of the bottom of my flight bag put some new AA batteries in it and after it figured out where it was, I put in the direct to KFYV task. I ran a tip tank dry west of Little Rock about 2 minutes before I planned to give up on it and switch to one of the main tanks (it takes a few seconds to regain power but the LASAR will work for a restart with the prop windmilling at a decent RPM). I declared minimum fuel and landed on the closer but downwind runway. All four red lights were on but three tanks still had fuel. Anyway, don't want to do that again - I'm thinking about a supported service loop and maybe two equivalent wires instead of one, with two terminals of course. Anyone else have the alternator wire breakage problem? What was your solution?

Bob Axsom

[dan]

Just confine the stress/flex/motion on the wire to a stretch between clamps, and don't allow any stress/flex/motion on any wire at the terminal end.

In other words, clamp (adel clamp, what have you) the wire somewhere a few inches from the terminal, clamped to something on the engine. That way there will be no stress imparted on the alternator end of the wire.

Then clamp the other end of the wire, a few inches from the other terminal end, clamped to the engine mount or something stationary relative to the engine.

That way the stress on the wire is confined to the stretch between clamps, and the terminal ends will experience no stress.

My 2 AWG starter wire broke at the contactor terminal because I hadn't properly clamped the wire in two places to eliminate the stress/flex at both ends. Eventually it will get ya. See what happened to mine:



And here's how I fixed it:



The key was clamping that wire in two places.

Hope this helps.

[Bob Axsom]

Thanks for that input. I have mine butterfly clamped off of the oil return lines but it is not imobilized. The butterfly is modified with a small piece of angle in the middle to get the alignment I needed. I have used MS21919DG-something that is compatible with these lines but there is not enough friction to do anything but hold the wire clear of chafe and heat locations. I had thought of using the proper sized uncushioned metal clamp for the line end of the butterfly to solidify the support. I may still do that but I will look for other mounting options as well. I assume that your experience has been good since the change.

Bob Axsom

[dan]

Originally Posted by Bob Axsom

I assume that your experience has been good since the change.

Yep. Haven't had a problem since. I had problems with the Lightspeed ignition coil wires in this same fashion early on -- I didn't do a good enough job with strain relief. Fixed that, fixed the starter wire, and while I was at it I beefed up the way the engine ground strap was double-clamped. Since doing all that, I haven't had any issues. Been keeping a close eye on all of the FWF wiring, so far so good. We'll see what the next few hundred or few thousand hours bring, but I don't expect any issues at this point.

[Bob Axsom]

The Wire is not broken and I have three clamp supports (one is more of a standoff) along the run from the firewall to the alternator. Not believing in coincidence, I suspect some internal damage to the alternator.

Bob Axsom

[L.Adamson]

A year ago, we ran into another variation of loosing the alternator with a RV9A. I don't know if the wiring was pre-made or not.

While in flight, the alternator voltage dropped, we landed at the nearest airport, took off the cowl, and tightened the alternator belt a bit more. Couldn't see anything else wrong.

On the ground, everthing now seemed to work fine, but once airborne, and under higher electrical loads, the voltage dropped again.

This time, we took off the alternator (Van's 60 amp) to have it checked out. I just happened to notice some blackness which looked like electrical arcing on the wire where it crimped to the terminal fitting. Pulling on the fitting, the wire just came right out.

New terminal fitting, and everything works great, including the alternator.

L.Adamson

[Bob Axsom]

When I got down to the terminal today I found that it was covered with black shrink fit sleeving. I cut that off and I found a large blue insulated terminal crimped in place. I cut that off and I found the terminal barrel crimped multiple times with a makeshift crimper; between the wire insulation and the terminal many strands are fractured with fatigued copper showing in the wire behind the crimp; and finally the shielding has strands that extend up to the exposed primary conductor. I pulled on the wire and it does not have that feel that gives you confidence but it did not pull out of the terminal. I already ordered a new wire and terminals to redo the job using my several hundred dollar crimper form Aircraft Spruce (oh how I wrung my hands before buying that one during the build process) with solid clamping support to the engine and good strain relieving service loops. You input gives me some hope that this may solve the problem. I'll try that anyway then press on if it doesn't work.

Thanks for the good input.

Bob Axsom