broken alternator wire. why did it fail?

rbridges

rbridges

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rbridges
I just had my alternator replaced in September. Maybe 20 hours since then. Flying home yesterday, my alternator quit charging. When I landed and removed the cowl, I saw this broken wire. I figure that's the problem, but I'm wondering why it broke. It looks like a clean break. Was it simply overcrimped? I just want to make sure I'm not overlooking a bigger issue. PXL_20220212_210422885.jpg PXL_20220212_210740840.jpg
 
The wire vibrates, the engine vibrates, everything vibrates. Any flex is going to occur right at the edge of the crimp, and eventually it works it enough that it breaks. Not at all unusual.
 
A little hard to tell from the pictures but the terminal looks too big for the wire so there was nothing to help support it. Also looks like a little corrosion. I would cut the wire back until I found corrosion free material, put a proper connector on that will heat shrink to the insulation.
 
how much distance to the where the wire is secured to something? iow - how long a wire run that would vibrate at the crimp?
 
Jim K said:
The wire vibrates, the engine vibrates, everything vibrates. Any flex is going to occur right at the edge of the crimp, and eventually it works it enough that it breaks. Not at all unusual.
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That's what I thought, too, but it just got installed. I'll see if they can do something to help support it better.
 
Didn't help that the insulation was not crimped.
You don't want an abrupt change in stiffness that concentrates the bending in one spot.
As mentioned above, supporting closer to the crimp, some heat shrink...
 
Maybe it’s just the picture, but frankly that whole assembly looks wonky to me. Big ass terminal at the bottom with a washer on top of that that isn’t big enough and then this terminal, which doesn’t like like the bolt is holding it flat even. I think you have more to deal with than the wire. JMO
 
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Now that I look at it closer, that terminal on the bottom is way too big for the bolt holding it. Then the washer on top of it is not big enough and has slid into it partially making it canted so that you aren’t even getting a good grip on the terminal that failed. That whole mess just ain’t right.
 
rbridges said:
but I'm wondering why it broke. It looks like a clean break. Was it simply overcrimped?
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My SWAG is the terminal wasn't changed and was existing (as are the other terminal) and set up for the previous alternator hardware. As why it broke, as mentioned above the environment, the wire stripper jaws cut into the conductor at one time, or the use improper tools to crimp can leave that result. Or the recent work performed aggravated an existing fault in the wire. From what you've posted I don't see any issue other than fixing the broken wire and clean up that entire ground connection to spec.
 
My first question would be "who the hell installed this and why the hell was he/she touching my aircraft?"

Seriously, this connection is so wrong whoever installed it shouldn't go back to working on go carts,

Improper use of crimping tool, or used a non-aviation crimper. The part of the connector that is supposed to grip the insulated part of the wire was never crimped.

Also, no use of strain relief.

Also, there is zero reason for the extra length of looped wire.

Also, the ***hat who did this left a nice sharp edge on the zip tie assuring someone is going to cut themselves sooner or later. Idiot didn't even use a simple flat cutter on it.

I would absolutely go back to the shop with these photos an scream bloody murder if it was me.
 
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Yeah, that crimp looks like it wasn't made with a proper die. Looked at from the end, it looks flattened rather than crimped.
 
Dynamic balancing can reduce the vibration. Do the other stuff first. Then make sure the engine runs very smoothly. -Skip
 
You paid someone to fix it and they didn’t have the part and took a shortcut. That’s what it seems like.
 
Bell206 said:
My SWAG is the terminal wasn't changed and was existing (as are the other terminal) and set up for the previous alternator hardware. As why it broke, as mentioned above the environment, the wire stripper jaws cut into the conductor at one time, or the use improper tools to crimp can leave that result. Or the recent work performed aggravated an existing fault in the wire. From what you've posted I don't see any issue other than fixing the broken wire and clean up that entire ground connection to spec.
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I think you're correct about reusing the terminal and wires. That makes me feel a little better about the wire breaking.
 
Lndwarrior said:
My first question would be "who the hell installed this and why the hell was he/she touching my aircraft?"

I would absolutely go back to the shop with these photos an scream bloody murder if it was me.
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Thanks for all the input! It's ironic because I went to a well respected shop. At this point, it's easier and cheaper to have a local IA fix it versus the cost and aggravation of flying to the other shop.
 
Unfortunately, electrical is not something the majority of mechanics understand so I’m not at all surprised to see an installation job like this. That doesn’t make it right, but it is what it is.

If it were me, I would call the mechanic/shop and have them take a look at it. Perhaps they will fix it free of charge, and you could ask them to clean up the wiring a bit. You had your alternator replaced, there was no conversion or upgrade being done (at least based on the original post) so I would guess that the wiring was just removed and reinstalled on the new alternator with no changes or repairs. So who knows how long it has really looked this way?
 
kyleb said:
Next time, use a piece of shrink wrap as an extended strain relief to keep all of the flex from happening at the crimp. Cover an inch of the wire and the body of the terminal.
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Exactly. In severe cases I have doubled the shrink wrap with the outer one shorter to spread out the stress even further,
 
rbridges said:
Thanks for all the input! It's ironic because I went to a well respected shop. At this point, it's easier and cheaper to have a local IA fix it versus the cost and aggravation of flying to the other shop.
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Please, at least send them the photos so they won't allow the person who did this do it to someone else's aircraft. This is a serious case of incompetence that could have a very bad outcome for someone in IMC with a single alternator.
 
If this is a 4 cyl engine with a front mounted alternator, the whole assembly is exposed to a 2/rev vibration around the vertical axis thru the engine CG due to the dynamics of any opposed engine with 4 cylinders. That's probably what fatigued the connection off. The wire has probably been vibrating in a blur at cruise rpm. Cleaning up and correcting the termination and crimp should help, but keep an eye on it anyway. The fatigue environment at those frequencies (about 80 Hz at 2400 rpm) can do funny things. Prop balancing only removes 40 Hz frequency components.
 
The extra wire looped around adds mass and inertia to the wire. Vibration does the damage. It should have been clamped to the alternator close to the terminal, which can't be expected to deal with strain and vibration.

I've found the terminals themselves broken due to vibration. They're just tinned copper, and copper work-hardens and fails quickly.
 
The end of the crimp on the terminal looks flat like it was crimped with a vise or hammered. I would want to cut away the insulation and see if this crimping method cracked the terminal. Whenever I crimp any wire above 10 gauge, I like to use my hydraulic crimper which works a lot better and you need good quality terminals. I also use heatshrink tube about two inches for additional stress relief. You can get a fairly good hydraulic crimper on Amazon for around $35. The length of wire looked a little short which may have created stress on the terminal.
 
This....the wire needs strain relief. I'd have several layers of heat shrink over the connector and wire.
kyleb said:
Next time, use a piece of shrink wrap as an extended strain relief to keep all of the flex from happening at the crimp. Cover an inch of the wire and the body of the terminal.
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It looks like it was crimped with a cheap crimper, not a ratcheting crimper that will get the correct crush on it and will also crimp the insulator end. The cheap crimpers are no longer acceptable. Been like that for 12 years or more. Refer to AC 43.13-1B for info on that.
 
This has been very educational for me. Anyway, here is another pic. It looks like a boot was left off. I don't know if that would have helped. As far as the wire length, should I have them cut of the excess? I don't see a way to secure the wire. PXL_20220213_190502695.jpg
 
Dunno that there was a boot. But on the bright side, you have more than enough wire to make a repair.
Cut off about half, new connector plus some shrink tube, crimp (including the insulation), shrink, done.
 
rbridges said:
It looks like a boot was left off. I don't know if that would have helped. As far as the wire length, should I have them cut of the excess? I don't see a way to secure the wire.
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FYI: boots are technically not required on ground connections. As to a shorter wire sure, but I'm a big fan of having a "service loop" on all wires, even ground wires. That said with a little reposition of all those wires you could get them better secured. But cleaning/resecuring/sealing that ground connection at the painted mount would be my 1st focus.
 
Bell206 said:
... As to a shorter wire sure, but I'm a big fan of having a "service loop" on all wires, even ground wires.
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as an aside, I believe I understand the reason for "service loop", but since that necessary wire length is so short would a service loop be all that important or useful?
 
The service loop could make it worse....it adds mass and will move more with vibration. Probably not significantly more....but the extra mass doesn't help.
Bob Noel said:
as an aside, I believe I understand the reason for "service loop", but since that necessary wire length is so short would a service loop be all that important or useful?
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That's a brush ground wire, and it only needs to be just long enough to reach between the brush terminal and the ground screw. Two inches max. And crimped with the proper crimper. Boots won't add anything to it except cost. It's at ground potential.

Normally that brush is grounded to the lower brush holder screw a half-inch away. It's hidden by the boot on the wire in that picture.

There is still a problem. The alternator ground cable is clamped under the cooling shroud screw and is angled by the screw depression in the shroud, putting a bending force (and poor contact) on the screw. There should be a dedicated ground stud on that alternator for that.
 
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Shop or not, I think you’ll find that this work was done by a non mechanic type.
 
Bob Noel said:
would a service loop be all that important or useful?
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Checkout_my_Six said:
The service loop could make it worse...
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Having replaced more short wires than long wires, I always go long and take care of the extra length properly by repostioning/rerouting the wires to achieve that. In this case I would have flipped over the small grd wire and had it supported by the larger case ground wire. Just one of a dozen ways to do it. But as Dan noted the larger ground connection is not correct and needs to be done better which could involve a longer version of the wire in question.
 
Thanks to everyone for the help. I had an A&P replace the end. He shortened the wire, made sure to include the insulation. He also shrink wrapped it. I'm sure we could have made a few other adjustments, but this has to be a 100x better. Alternator is back online.
 
rbridges said:
Thanks to everyone for the help. I had an A&P replace the end. He shortened the wire, made sure to include the insulation. He also shrink wrapped it. I'm sure we could have made a few other adjustments, but this has to be a 100x better. Alternator is back online.
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Yay! I was hoping someone would post a photo of the tools and parts needed because that is definitely simple. How much did it run you?

Would be nice if POA has a maintenance and corresponding price to repair section to start to establish some market norms.
 
mandm said:
Would be nice if POA has a maintenance and corresponding price to repair section to start to establish some market norms.
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FYI: there are zero market norms with aircraft maintenance as cost is very subjective to the owner, aircraft, provider, and location. Nor has it ever been.
 
mandm said:
Yay! I was hoping someone would post a photo of the tools and parts needed because that is definitely simple. How much did it run you?

Would be nice if POA has a maintenance and corresponding price to repair section to start to establish some market norms.
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I got lucky. A guy two hangars down who is an A&P repaired it for free. I was just asking his opinion, and he ended up fixing it. Took him 20 minutes.
 
Lots of references on the internet. https://www.fscables.com/sites/admin/plugins/elfinder/files/fscables/other pdf/cablecraft_crimp_guide.pdf
I think splices and terminals that meet mil specifications for aviation use are best. Modern crimpers and dies will have inspection marks or witness points that let an inspector verify proper tools and methods were used. I've seen airline repairs that look like they were done with vise grips.

There is a lot of mechanical design and metallurgy behind well designed vibration tolerant wire connection systems. A lot of things that look simple aren't necessarily.
 
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