Can anyone share a picture of their installed Alternator wiring?

[Vance Harral]

Trying to debug an alternator problem and would appreciate some pics.

Aircraft is a 1976 M20F with a Hartzell ALY-8520 alternator.  Alternator was removed during our recent annual and sent to a repair shop for IRAN, due to significant electrical noise that did not seem to be caused by loose connections.  The alternator shop reported they "found a broken wire" internally, and that the alternator was full of grime (mostly oil leaked from the motor).  Broken wire was supposedly fixed and everything cleaned, but I do not know if the re-assembled alternator was actually bench tested.  In this time of social distancing, I also was not able to participate in or observe the alternator being re-installed in the aircraft.  The mechanic that did the work completed the annual taxied the airplane back to our hangar a couple of days ago, and unfortunately reports that the re-installed alternator does not appear to be working at all: he saw a discharge on the ammeter and a flashing voltage light from the voltage warning system.  He has offered to work with us to resolve the problem, but the airplane is no longer in his shop, it's back in our hangar.

One possibility is that the IRAN shop botched the job and broke our alternator, but I'm hoping it's just a simple wiring error committed on the re-installation.  I'm headed to our hangar tomorrow with flashlights, mirrors, and a voltmeter to take a look.  I don't actually have an installation manual for the ALY-8520, but based on manuals for similar alternators, the schematics for my airplane, and a rudimentary understanding of principles, I expect to check the following:

• ground terminal securely connected to airframe ground
• output terminal securely connected to large-gauge wire that goes to bus bar/ammeter shunt/regulator/voltage warning
• F1 field terminal securely connected to airframe ground
• F2 field terminal securely connected via small-gauge shielded wire through master switch to regulator
• AUX terminal not connected to anything

One thing that would be helpful is if I had a photo of the same or similar alternator, in a working Mooney of similar vintage.  Space is tight and even with mirrors and flashlights, I'm not sure I'm going to be able to tell which terminal is which.  Thanks in advance to anyone who can share a relevant photo.

[RLCarter]

F1 & F2 are are for the "Field" coil, I'm pretty sure neither should go to ground 

[N201MKTurbo]

The field wiring depends on the installed regulator. Some, including mine do have one of the field terminals grounded.

[Vance Harral]

The factory schematics for my aircraft show the F1 terminal grounded, see attached screenshot.  Current needs to pass from F1 to F2 for the alternator to work, but there is nothing wrong with one of those terminals being grounded.  I'd bet that installations which connect both F1 and F2 to the regulator likely have one of the connections internally grounded inside the regulator.

 

[RLCarter]

4 minutes ago, Vance Harral said:

The factory schematics for my aircraft show the F1 terminal grounded, see attached screenshot.  Current needs to pass from F1 to F2 for the alternator to work, but there is nothing wrong with one of those terminals being grounded.  I'd bet that installations which connect both F1 and F2 to the regulator likely have one of the connections internally grounded inside the regulator.

 

way to small for me to see and distorts too bad when enlarged but i think your seeing the shield going to ground

[Vance Harral]

The bottom of the circle that represents the alternator has a terminal dot labeled "1", which I take to mean "F1" of the Hartzell ALY-8520.  See slightly higher-res picture below.

The shields from the "+" and "2" wires do connect to the "1" terminal, but it seems clear to me that terminal "1" is itself grounded, and the shields are just conveniently connected there.  One thing that makes this obvious is terminal "1" obviously can't be left floating.  If it's not supposed to be connected to ground, what else would it be connected to?  The only leads emanating from that terminal are the wire shields and the ground connection.

 

[Guest]

This schematic is from a 1974, but should be similar enough.  F1 and F2 should be the field windings, they aren’t polarity sensitive.  Field power from the regulator should have 12 volts when the master and alternator field switches are on.  The output cable should also have 12 volts when the master switch is on.

Field power should be connected to either F1 or F2 the other should be to ground.  The ground wire typically goes to the ground stud on the alternator, there is a large ground cable that goes from the ground stud to the engine case.  The shielding wires from the field wire and the power output cable also go to the ground stud.  I have also seen the field ground wire grounded to one of the screws that hold the brush block to the alternator.

Once you verify the wiring is correct, turn on the master and alternator field switches the pulley shaft at the front of the alternator should become magnetic.

Clarence

Edited April 16, 2020 by M20Doc

[Vance Harral]

Actually headed out to the hangar later today.  Appreciate all the schematics.  Anyone happen to have pictures of an actual installation?

[Marauder]

2 hours ago, Vance Harral said:

Actually headed out to the hangar later today.  Appreciate all the schematics.  Anyone happen to have pictures of an actual installation?

I took pictures of my old ALY-8520 alternator before I removed it for a Plane Power unit. Will PM you the pictures. Not sure they will help.

[Vance Harral]

Marauder, your pictures are very helpful.  Thanks for taking the time to respond!

[gsxrpilot]

1 hour ago, Marauder said:

I took pictures of my old ALY-8520 alternator before I removed it for a Plane Power unit. Will PM you the pictures. Not sure they will help.

Would you mind sending me the pictures as well? My #1 alternator has gone off line and @Denver98 has discovered a broken wire at the alternator. Now trying to figure out where it goes.

[Vance Harral]

OK folks, here's a picture of the back of my alternator, with connections labeled.  I found several things of interest:

1. There is no large terminal on the back of the alternator actually labeled GROUND(-), which is surprising to me.
2. The large terminal the bottom of the picture labeled AUX has been wired to the engine case.  If this was not supposed to be grounded, I can forgive my mechanic for an honest mistake, because with no terminal actually labeled GROUND (-), the AUX terminal sure seems like the one to connect to ground.
3. The nut holding the ring terminal of the grounding wire to the AUX terminal of the alternator was loose.  So even though the mechanic intended to ground this terminal, it was probably making a marginal ground contact at best.

I don't have a manual for the ALY-8250, but I found another Hartzell alternator manual online that covers several models, and the diagrams for all of them have a really big, obvious GROUND terminal separate from the AUX terminal.  The ALY-8520 does not.  What deepens the mystery is that in the pics Maurader sent me of his ALY-8520, one of the small brass screws that holds the black plastic cooling shroud on the back of the alternator has a ring terminal attached to it.  Not sure what that would be for, except maybe to ground the case of the alternator to the airframe or engine (perhaps that's the missing ground connection in my installation!).  But if the GROUND connection on a Hartzell ALY-8520 is just the case of the alternator itself, I'd think the mounting bolts would provide sufficiently good ground.

Comments?

 

[Vance Harral]

The plot thickens...

Below are two photos of good installations: one from Marauder that I don't think he'll mind if I share, and another I took when I was trying to chase an oil leak a couple years ago.  Both photos show the AUX terminal not connected to anything.  Both photos show the brass cooling shroud screw between the F1/F2 terminals and the AUX terminal being connected to a ground wire, which in our case I think goes to the negative terminal of the landing light.

I don't actually think the purpose of the wire connected to the cooling shroud screw is to ground the alternator frame.  I think it's just a convenient place to tie something to ground.  My guess is the "main" ground of the alternator frame is the mounting bolt.  That said, in Maurader's photo, one of the things connected to the cooling shroud screw is clearly a grounding strap, and in my photo the cooling shroud screw is clearly connected to the oil pan.

 

[N201MKTurbo]

The aux terminal is usually another set of diodes in a 1/2 wave rectifier. It is usually used for alternator failure lights.

If you ground the AUX terminal, you will probably blow the aux diodes. But we don’t use them for anything, so no problem.

[Vance Harral]

The schematic below is from a different set of Hartzell alternators, not the ALY-8250.  But if the ALY-8250 is wired the same way, I don't think grounding the AUX output can actually damage any diodes.  The center of the stator wye varies between output and ground voltage during normal operation (averaging about half the output voltage), regulated by the two diodes between it and the output/ground terminals; so it appears to be "normal" for it to be at ground potential at least part of the time.  I think all grounding the aux terminal does is reduce the EMF that can be generated in any of the stator coils.  In that configuration, I think the alternator could still produce rated output if the field current was high enough.  But my guess is the max field current the voltage regulator can produce is insufficient to produce rated output  when the aux terminal is shorted to ground (as opposed to connected through a charge warning lamp or other nonzero load).

Of course, I could be wrong.  Electrical machines were never my forte, I'm a digital guy at heart.

[chriscalandro]

Use the schematic from the devices you have. 
 

do not use pictures of random alternators on the internet to troubleshoot your wiring.  That’s how fires start.  
 

all the information you need should be on the manufacturer page. 
 

based on the conversation here this is NOT something I believe you should be messing with yourself and you should consult a professional or someone who knows how to read the drawings. 

Edited April 18, 2020 by chriscalandro

[Vance Harral]

8 minutes ago, chriscalandro said:

all the information you need should be on the manufacturer page

Should be, but isn't.  If anyone actually has a manual for the Hartzell/Prestolite ALY-8520, let me know.  Absent that, other Hartzell alternator manuals are the only reasonable source.

10 minutes ago, chriscalandro said:

you should consult a professional or someone who knows how to read the drawings

I am a professional electrical engineer, working directly with a professional A&P.  Short of trucking the entire airplane with the alternator in situ to the Hartzell/Prestolite/Kelly Aerospace/Whoever-owns-the-rights-this-year factory, this is as good as it gets.

[chriscalandro]

On 4/15/2020 at 7:37 PM, Vance Harral said:

I don't actually have an installation manual for the ALY-8520, but based on manuals for similar alternators, the schematics for my airplane, and a rudimentary understanding of principles, I expect to check the following:

The sentence above and your last comment don’t quite match up so you can see where I may have been confused. 
 

it looks very much like the mounting bolt at one time had a ring connected to it. 
 

you’re right. I couldn’t easily find a drawing but it should be in your maint manual. 

[Vance Harral]

12 hours ago, chriscalandro said:

it looks very much like the mounting bolt at one time had a ring connected to it. 

That's a good point about the witness marks around the mounting bolt.  But it would be unusual to put an electrical ring terminal around a truly structural mounting bolt.  And while it's tough to tell from the UV blacklight photo I posted above, I don't think I see any wiring going to the mounting bolt.

My plan today is to head out to the airport, disconnect the wire from the AUX terminal, and try a ground run.  If that resolves the problem, I'll have the A&P come take a look too.

[Vance Harral]

To close up the thread: got out to the hangar today as planned.  Disconnected the ground wire from the AUX terminal, and alternator is now working as designed.  The ground wire that was connected to the AUX terminal shares a ground connection with the shielding cable for the primary lead.  So the wire needs to be grounded, but not the aux terminal of the alternator.

Thanks to all who offered help in this thread, I appreciate it.

[chriscalandro]

Huh?

in order for there to be a Complete circuit there must be.... a circuit. 
 

What exactly are both sides of the alternator circuit connected to?

Edited April 18, 2020 by chriscalandro

[Guest]

On 4/17/2020 at 6:19 PM, Vance Harral said:

OK folks, here's a picture of the back of my alternator, with connections labeled.  I found several things of interest:

1. There is no large terminal on the back of the alternator actually labeled GROUND(-), which is surprising to me.
2. The large terminal the bottom of the picture labeled AUX has been wired to the engine case.  If this was not supposed to be grounded, I can forgive my mechanic for an honest mistake, because with no terminal actually labeled GROUND (-), the AUX terminal sure seems like the one to connect to ground.
3. The nut holding the ring terminal of the grounding wire to the AUX terminal of the alternator was loose.  So even though the mechanic intended to ground this terminal, it was probably making a marginal ground contact at best.

I don't have a manual for the ALY-8250, but I found another Hartzell alternator manual online that covers several models, and the diagrams for all of them have a really big, obvious GROUND terminal separate from the AUX terminal.  The ALY-8520 does not.  What deepens the mystery is that in the pics Maurader sent me of his ALY-8520, one of the small brass screws that holds the black plastic cooling shroud on the back of the alternator has a ring terminal attached to it.  Not sure what that would be for, except maybe to ground the case of the alternator to the airframe or engine (perhaps that's the missing ground connection in my installation!).  But if the GROUND connection on a Hartzell ALY-8520 is just the case of the alternator itself, I'd think the mounting bolts would provide sufficiently good ground.

Comments?

 

If this picture is of your installation I’d suggest a few things.  Both of the field wire terminals could stand replacing with new ring terminals, the output terminal could stand the same thing.  Both of these terminals should have insulating protective boots installed, MS25171-1S for the smaller and -2S for the larger.

Clarence

[Vance Harral]

29 minutes ago, chriscalandro said:

in order for there to be a Complete circuit there must be.... a circuit. 
What exactly are both sides of the alternator circuit connected to?

The lack of a separate ground terminal indicates the (-) node of the circuit is internally connected to the metal alternator case.  Because the case is mounted to the airframe, the mounting bolts effectively serve as the ground connection.  Most automotive alternators work this way.  Here's a typical image, note the ground connection being shown as the case:

[chriscalandro]

Ok, I see what you’re saying. I thought you said the shielding of the wire you put as a ground somewhere.  Which raised all sorts of flags in my mind. 

[Vance Harral]

11 minutes ago, M20Doc said:

Both of the field wire terminals could stand replacing with new ring terminals, the output terminal could stand the same thing.

The field wire to F1 should just be replaced entirely, it's obviously quite old.  The other's don't look too bad to me in person, but I appreciate the caution.

15 minutes ago, M20Doc said:

Both of these terminals should have insulating protective boots installed, MS25171-1S for the smaller and -2S for the larger.

The output terminal does have a boot, it's just pushed out of the way for the photo.  You can see part of it at the upper right of the picture.

Putting a boot on F1 makes sense, that's the output to the field terminal from the regulator.  I'll take that into consideration when the associated wire is replaced.  The wire on F2 just goes to ground, I don't think it needs a boot.