Hot alternator?

[will1874]

Hello all, 

I took the family on their very first cross-country adventure today. Left KBDR for KFCI. That leg was uneventful and everyone loved it. Got out at KFCI, fueled up, ate at the restaurant, and got back at it. Next leg was KFCI to KHXD. 

It was hot. Probably close to 90 on the ramp. Took off and headed south. Climbed up to 8000' I kept noticing a very faint whine...almost alternating like the gear warning but not nearly that loud. I thought it must be some sort of feedback from a headset or radio or something.  Once we leveled off and reduced RPM for cruise I started trying to troubleshoot. Then I saw it. Very faintly the HIGH LOW VOLTAGE warning light was flickering. Not flashing like when you're not producing any electricity. I reset the alternator field CB. Whine immediately went away when I pulled it. Came back when I reset the CB. I decided to divert to KRDU. Eventually the flickering stopped. Seemed like the faint whine did too. But it was tough to tell while we were getting the stuffing beat out of us on the way down into RDU. 

Like I said it was hot. The hottest cylinder head temps I've seen. Still in the green, but near the top of the gauge. (I do not have an engine monitor). 
 

is it possible the alternator overheated? 

[carusoam]

Alternators are known to create whines….. usually when one of its diodes has taken leave…

Best regards,

-a-

[PT20J]

Sounds like a failing diode.

[N201MKTurbo]

The diodes rarely fail, but the diode connections do fail from vibration. Doesn’t make much difference unless you are prone to fixing things. Ive been able to resolder  the diodes a few times and fix that problem.

[will1874]

18 minutes ago, N201MKTurbo said:

The diodes rarely fail, but the diode connections do fail from vibration. Doesn’t make much difference unless you are prone to fixing things. Ive been able to resolder  the diodes a few times and fix that problem.

Do you mean I just need a new alternator unless I'm good at fixing things? (I'm not prone to fixing anything). 

[N201MKTurbo]

12 minutes ago, will1874 said:

Do you mean I just need a new alternator unless I'm good at fixing things? (I'm not prone to fixing anything). 

Probably. If you lost one diode you will lose 1/6 of your capacity, so you can live with that until the whine drives you crazy.

[kortopates]

Do you mean I just need a new alternator unless I'm good at fixing things? (I'm not prone to fixing anything). 

Don’t need to replace it, unless you’re in a hurry and have bags of cash. Much less expensive to have your mechanic send it out to an electrical repair station. they’ll advise what it needs and you can elect to just fix or overhaul it once they give you an assessment.
Aero Accessories in Van Nuys, CA turns them around in usually a day.



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[N201MKTurbo]

14 minutes ago, will1874 said:

Do you mean I just need a new alternator unless I'm good at fixing things? (I'm not prone to fixing anything). 

Probably. If you lost one diode you will lose 1/6 of your capacity, so you can live with that until the whine drives you crazy.

[philiplane]

Losing a diode means you now have some AC in your DC system. You need to repair or replace the alternator ASAP.

The purpose of the six diodes is to clip off the high and low AC pulses, to help rectify the AC to DC.

[BaldEagle]

44 minutes ago, kortopates said:

Don’t need to replace it, unless you’re in a hurry and have bags of cash. Much less expensive to have your mechanic send it out to an electrical repair station. they’ll advise what it needs and you can elect to just fix or overhaul it once they give you an assessment.
Aero Accessories in Van Nuys, CA turns them around in usually a day.



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That’s where mine was sent to a couple of weeks ago.  Aero Accessories are awesome, highly recommended.  They turned it around in 24 hours and for a very reasonable price.

[takair]

Will,  Sounds like you are on the road with this problem.  Does the plane have a voltmeter?  If so, you can get a sense of what’s going on by reading that.  Typically you want to be near 14….but can manage on less, as long as it’s charging somewhat (something greater than 12….under reasonable load).  If you don’t have one, you might temporarily get by with a cigarette lighter style that you can pick up locally.  That way you can at least do a local flight to see what the problem looks like after things cool down.  It might be your ticket home….VFR of course.  You might also play with electrical load to see if you can get it lower and still get home….

[N201MKTurbo]

An alternator with a missing 1/2 phase should still make its normal voltage. The regulator will just give more field current to get the required voltage. The alternator will just have less current capacity. Your alternator rarely uses its full capability, so you will probably not notice any problems except the whine. If the alternator will not maintain normal voltage after the battery is charged, you have problems beyond a single diode failure.

[will1874]

9 hours ago, takair said:

Will,  Sounds like you are on the road with this problem.  Does the plane have a voltmeter?  If so, you can get a sense of what’s going on by reading that.  Typically you want to be near 14….but can manage on less, as long as it’s charging somewhat (something greater than 12….under reasonable load).  If you don’t have one, you might temporarily get by with a cigarette lighter style that you can pick up locally.  That way you can at least do a local flight to see what the problem looks like after things cool down.  It might be your ticket home….VFR of course.  You might also play with electrical load to see if you can get it lower and still get home….

I do have the simple cigarette lighter voltmeter. And we were bouncing between  14 and 13.8. I'll probably just bring it to a good shop on the way home. 

[will1874]

10 hours ago, takair said:

Will,  Sounds like you are on the road with this problem.  Does the plane have a voltmeter?  If so, you can get a sense of what’s going on by reading that.  Typically you want to be near 14….but can manage on less, as long as it’s charging somewhat (something greater than 12….under reasonable load).  If you don’t have one, you might temporarily get by with a cigarette lighter style that you can pick up locally.  That way you can at least do a local flight to see what the problem looks like after things cool down.  It might be your ticket home….VFR of course.  You might also play with electrical load to see if you can get it lower and still get home….

I do have the simple cigarette lighter voltmeter. And we were bouncing between  14 and 13.8. I'll probably just bring it to a good shop on the way home. 

[takair]

4 hours ago, will1874 said:

I do have the simple cigarette lighter voltmeter. And we were bouncing between  14 and 13.8. I'll probably just bring it to a good shop on the way home. 

Sounds like you are in fairly good shape. For what it’s worth, some planes just have a slight whine even with a good alternator. The ground path can cause this. I’ve also seen some pick up noise from things like the display on certain radios. This can be especially prone on bright days when the display is pushed to the limit. Could also be the voltage regulator cycling at the 14 v limit. Hope you can make your destination too and enjoy the trip. Still looking forward to meeting you. Must keep passing each other at the airport.