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Alternator inspection - How to do

LarryT

Well Known Member
I previously posted about the unbearable noise in my intercom system. One responder suggested that I may "lost a rectifier" in the alternator.

I now have the alternator out of the aircraft. There is no identification on the alternator at all. There is a "B" lead and one other wire connection to the alternator, which I assume is a field wire. The field wire goes into a plug that originally had three leads, but two have been removed. Does that mean there is an external voltage regulator somewhere? I bought this aircraft flying, so I am not familiar with every detail of its construction.

Would one of you electrical geniuses please tell me how to inspect this alternator for a blown rectifier (diode).

I took a picture of the alternator and the three prong connection. If you need photos to help out, please PM and I will e-mail them to you.

Thanks

Larry Tompkins
544WB -6A
W52 Battle Ground WA
 
I previously posted about the unbearable noise in my intercom system. One responder suggested that I may "lost a rectifier" in the alternator.

I now have the alternator out of the aircraft. There is no identification on the alternator at all. There is a "B" lead and one other wire connection to the alternator, which I assume is a field wire. The field wire goes into a plug that originally had three leads, but two have been removed. Does that mean there is an external voltage regulator somewhere? I bought this aircraft flying, so I am not familiar with every detail of its construction.

Would one of you electrical geniuses please tell me how to inspect this alternator for a blown rectifier (diode).

I took a picture of the alternator and the three prong connection. If you need photos to help out, please PM and I will e-mail them to you.

Thanks

Larry Tompkins
544WB -6A
W52 Battle Ground WA

Local automotive shops will be able to test it and determine if everything is ok.
 
with it running, hook up your DVOM and select AC, one lead on B+ and other on alt case. if you see AC voltage you have a leaking diode.
 
Alternator update

I took the alternator in to the Auto Parts store and they checked it out has good. Passed all three tests including diode check 14.82 V; Ripple 0.49

This testing was done to see if I had a blown diode that was screwing up my Flightcom 403 intercom.

If this test eliminates the alternator as a noise source, please look at mu Flightcom 403 doorstop thread to see if you can offer any suggestions.

Thanks,

Larry
 
If this an externally regulated alternator, then another source of noise can be due to poor connections to the regulator.

I have an externally regulated alternator on my RV-9A. I used to have quite a bit of noise in the system that got worse as electrical loads were added. The fix was to directly connect the regulator to the battery with a relay controlled by the field switch. Search the threads for more information.
 
Does the aircraft in question here have an SL30?

This is s long shot but if so Check the NAV button on the SL30. I have seen a similar issue with the NAV button being on ID or VOICE and forgetting to switch it back to out. If that does not help, tune to a different VOR. Have seen a couple of VORs that was transmitting static or at least my NAV picked up static when I was tuned to it. When you ID a VOR, you need to press the NAV button TWICE to get back so that there is no noise on the NAV radio audio output.

If using any other nav/com check that the ID tone has been turned down or silenced.

Also check the squelch setting if only a stand alone com radio.

Lastly, several years ago I had to install a noise suppressor in the power line just before the com radio to silence an issue similar to what you describe.

Good Luck.
 
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Replies to posts 5,6,& 7

#5 Vern, I think it must have an external regulator. There is plug with three spade connections that plugs into the back of the alternator. However 2 of the 3 wires and connectors have been removed.

Can you confirm that means what is left is the field wire and it necessarily has to pass through an external regulator in order for field current to be turned on and off.

#6 Please remember that I am an electrical dummy. What capacitor?

#7 Not an SL 30. there is one radio and it is an Icom. Did you install the noise suppressor to address a problem that got worse over time?

FWIW. When I am in the ISO position, I get a clear side tone and 5x5 when I ask for a radio check. There is some background static receiving transmissions in ISO. In the ICS switch position background static increases significantly and the unbearable whistle comes in. That static and whistle was not present when I operated the radio in my hangar with the engine off.

I thought the radio and intercom worked quite well when I bought the plane four years ago. This is an issue that reared its ugly head after the plane had sat for some time without flying due to my own economic issues.

Hope this helps some of you who know something. I freely admit that I know nothing about electricity. I had to take 2 EE courses to get my mechanical engineering degree. I believe that I flunked the second one but was given a passing grade because the professor never wanted to see me again.

Larry
 
Replies to posts 5,6,& 7

#5 Vern, I think it must have an external regulator. There is plug with three spade connections that plugs into the back of the alternator. However 2 of the 3 wires and connectors have been removed.

Can you confirm that means what is left is the field wire and it necessarily has to pass through an external regulator in order for field current to be turned on and off.

#6 Please remember that I am an electrical dummy. What capacitor?

#7 Not an SL 30. there is one radio and it is an Icom. Did you install the noise suppressor to address a problem that got worse over time?

FWIW. When I am in the ISO position, I get a clear side tone and 5x5 when I ask for a radio check. There is some background static receiving transmissions in ISO. In the ICS switch position background static increases significantly and the unbearable whistle comes in. That static and whistle was not present when I operated the radio in my hangar with the engine off.

I thought the radio and intercom worked quite well when I bought the plane four years ago. This is an issue that reared its ugly head after the plane had sat for some time without flying due to my own economic issues.

Hope this helps some of you who know something. I freely admit that I know nothing about electricity. I had to take 2 EE courses to get my mechanical engineering degree. I believe that I flunked the second one but was given a passing grade because the professor never wanted to see me again.

Larry
 
Hi Larry. At this point, it's time to have someone with avionics experience go through your aircraft. Since you didn't build it, you don't know how it was put together.

The fact that in ISO mode, it works fine is a good sign. In ISO mode, your headset and mic are directly connected to your comm, and the intercom is offline.

This means that the intercom or its associated wiring is at fault. My bet is the wiring is at fault. This can be determined by swapping the intercom with a known good unit.

Get professional help!
 
#5 Vern, I think it must have an external regulator. There is plug with three spade connections that plugs into the back of the alternator. However 2 of the 3 wires and connectors have been removed.

Can you confirm that means what is left is the field wire and it necessarily has to pass through an external regulator in order for field current to be turned on and off.
This probably is internally regulated. There is likely a Field breaker and maybe going through an Alt switch, but no external regulator.
FWIW. When I am in the ISO position, I get a clear side tone and 5x5 when I ask for a radio check. There is some background static receiving transmissions in ISO. In the ICS switch position background static increases significantly and the unbearable whistle comes in. That static and whistle was not present when I operated the radio in my hangar with the engine off.

I thought the radio and intercom worked quite well when I bought the plane four years ago. This is an issue that reared its ugly head after the plane had sat for some time without flying due to my own economic issues.

Hope this helps some of you who know something. I freely admit that I know nothing about electricity. I had to take 2 EE courses to get my mechanical engineering degree. I believe that I flunked the second one but was given a passing grade because the professor never wanted to see me again.

Larry
It sounds like you may have a bad passenger/copilot jack or possibly a short in the jack (part touching ground that shouldn't be). Try pulling those jacks out of the panel and let them hang without touching each other and see if that changes anything.
 
I thought the radio and intercom worked quite well when I bought the plane four years ago. This is an issue that reared its ugly head after the plane had sat for some time without flying due to my own economic issues.

Check all the ground(s) but especially those to your intercom and radios. If it worked OK before and now it doesn't after sitting around for some time you could have some corrosion at the ground point or a loose connection causing the problem.

Long shot, but worth the try before spending any $$$ on equipment.

:cool:
 
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