Broken Alternator Shroud

DanH · #1 11-20-2011, 08:20 PM

Has anyone seen this before? Plane Power alternator....works fine but the cooling shroud appears to have vibrated to death.

I'll check the ring gear sheave for out-of-round. Beyond that thought I am at this moment clueless.

AlexPeterson · #2 11-20-2011, 08:35 PM

Wow, not sure what I'm looking at. Can you outline where the chunk is missing? The shroud looks stout enough where it would be tough to get into resonance.

chaskuss · #3 11-20-2011, 08:36 PM

Dan,
Check your alternator mounts. Make sure they are secure. I would suggest you attempt to stiffen the mounting of your alternator. The PP unit is based on the "small" ND [30 to 60 amp] alternator. The pivot point on these units only extends a bit more than 50% of the alternator's depth. The large ND units extend 100% of their depth. In automotive use, the slotted adjustment bracket is always triangulated [3 mounting points, including the alternator]. Vans bracket does not give you the same stiff mount that the original automotive applications do.
Charlie
PS The pivot mount on the small ND units only attaches to the forward section of the alternator housing. The larger ND units [60 to 95 amps] have the pivot mount cast into both the forward and rear ward sections of the case.

jclark · #4 11-21-2011, 12:06 AM

Yes,

I have seen this on MY Plane Power (well almost). I caught it before it broke off and safety wired it. Those shrouds seem to be made of VERY thin metal and with a little shaking, it cracks.

I had planned to call Plane Power about it but since you have one that has BROKEN OFF, I think you have a better "case" to find out what is happening.

If you get an answer, please post.

Thanks,

chaskuss · #5 11-21-2011, 06:30 AM

Dan,
Check your private messages
Charlie

DanH · #6 11-21-2011, 06:42 AM

Quote:

Originally Posted by AlexPeterson

Wow, not sure what I'm looking at. Can you outline where the chunk is missing? The shroud looks stout enough where it would be tough to get into resonance.

Yeah, that surprises me too. As Mr. Clark says, the shroud material is quite thin, but shape and three mount points make resonance seem like a remote possibility. However, clearly it does resonate.

First point of failure was probably in the corner behind the B terminal, next to the case. The crack would proceed up the bend between the B and the plug, after which the rest would be short work.

A dot of silicone between the rectifier base and the shroud would kill the vibes.

This was hung on PP-supplied bolt-on mounts. The bracket and tension arm are both in good shape.

James, did yours break near the B post?

jclark · #7 11-21-2011, 06:56 AM

I noticed a crack in mine so I safety wired it to keep it from coming off.

Next time I have cowl off, I will make a note of where the cracking started and report back.

James

DanH · #8 11-21-2011, 07:36 AM

I previously said three mount points should discourage resonant vibration, but that's wrong. In the picture below you can see how the regulator side (on the right) lacks a mount screw or other support and is thus free to vibrate. The original failure was probably where marked, at a small-radius formed bend near the base of the B-terminal (some material is missing in this photo; I've drawn it in for illustration). The rest follows quickly.

Material appears to be 0.030" 1100 aluminum.

rocketbob · #9 11-21-2011, 07:53 AM

Score another one for the supposedly superior "designed for aircraft" alternators.

DanH · #10 11-21-2011, 08:37 AM

Just got off the phone with a nice lady at Plane Power. When I mentioned a broken shroud, she immediately asked "Aluminum or steel?", and then volunteered to send a new steel shroud at no charge. Good service.

Current production alternators get steel shrouds. If you have an aluminum shroud inspect it carefully at the next opportunity.