Front Alternator Inoperative
 

A few weeks ago, I flew my "new" 1973 T337G, pressurized, SN P3370063, N3CU, home to NH from IA, where I purchased it. A great flight.

Recently, upon starting the front engine, the alternator inoperative light either did not extinguish or came back on soon after engine start. The mechanic examined the connections and seemed to have solved the problem.

Thirty minutes into the next flight, the front engine alternator inoperative light came on again, with no overvoltage light.

In advance of asking the mechanic to tackle the problem again, I've been going through the various postings on the 337 websites relative to alternator problems. There are several references in those postings to comprehensive articles on the 337 electrical system written by GMAS, evidently a few years ago. I cannot now find the articles, so they must have been deleted.

Does anyone have the articles archived, or does anyone know of a comprehensive trouble-shooting guide I can provide the mechanic?

I realize that alternator problems are a rite of initiation, so I'm trying to take it all in good humor, but I would like to get to the bottom of the matter as soon as possible so I can get back to flying this wonderful machine. I need it for Sun 'n Fun and for the OKC 337 Fly-In.

Best,

GJ Humphrey

I went to Peter's website and looked in the archives, but the Airframe section is gone/lost and the Engine section doesn't have anything on alternators. So I went to this forum, clicked Search near the top of the page (between FAQ and Site Info), entered "alternator" and got lots of message threads dealing with the electrical system and the alternators. Didn't look at all, but the one I did open (Alternators....Regulators... and here we go again... ) had a long analysis by GMAs. That message and others found by the Search feature may prove valuable. I notice that you also posted your inquiry in Peter's message board, so GMAs will probably give you an answer -- if he doesn't get upset about you posting on both boards (no offense, GMAs, would love to have you back!)

Ernie

Front Alternator Inoperative
 

Thanks, Ernie.

Great minds think alike. I too had conducted a search of the SOAP site, using the word "alternator", and there's some great stuff in there, but I'm not sure I want to pay a mechanic to wade through all those many postings. That's why I am looking for a comprehensive article.

If anyone has GMAs' article on the electrical system archived, he/she would do us all a great favor by making it available by email upon request.

In the posting you cite, Alternators....Regulators... and here we go again..., GMAs says: some times the alternators have whine or ripple associated with them... how do we know.. we measure it with a AC volt meter... It can mess up your regulators ... regulation... yep... can make one seem out of adjustment.... when its not...

That reminded me, about the time the front alternator inoperative light came on, I heard a rippling whine in the headset. Is this what GMAs meant in his posting? If so, what is the cause and wht is the remedy? Does anyone know?

Best,

GJ Humphrey

Alternator problem-

1 With a voltmeter measure 28 volts at the BAT terminal on the ALternator.
2. Measure 28 volts on the field terminal of the Alternator.
3. Make sure the 40 amp circuit breaker is not out.
4. With a light look into the side of the alternator (you can seen the cooling fan) and make sure it turns.

If there is no voltage on the BAT terminal the 40 amp circuit breaker is blown.
If there is no field voltage the regulator is U/S.
If it does not turn the drive is sheared.

If all of the above is ok you have a U/S alternator.

Hope this helps

Peter Somers

I'd like to add one other possibility to Pete's excellent summary. On my 73, I have frequently seen alternator inop lights come on intermittantly, or even solid, due to unbalanced voltage regulators and other wiring faults (for example, lose diodes in assembly at top center of forward firewall - alternator warning circuit board). Here is an excellent thread on the subject of alternator problems. Bob Cook provides some good troubleshooting steps.

http://www.337skymaster.com/messages...=&threadid=604

Kevin

Check the coupling
 

Check the coupling! It may not be an electrical problem at all.

One problem that is quite often over looked with the alternator is the drive coupling. Quick check. Leave all switches off. Take front cowl off. Reach into the fan area of the alternator and see if you can turn it. If it can turn, the rubber coupling with a gear attached to it has to be replaced. This is a quick check before you start spending a lot of time and money chasing an electrical ghost.

Jerry
N34EC

I agree with take cowl off and check fins I had this only happen once but maybe it will do it again somewhere else . The woodruff key on the alternator shaft had broken and would spin on the shaft when it was a cold start or run it would catch and work but as the shaft would heat up it would no longer heat up and you will get the alt out lite come on saying not charging....Jack

if it is a p there are no circuit brerakers, the dioades are use for protection. last week on a trip north the all alt lights came on, did all the remidies but no avail. the bat just kept going going down. turned all equip off. called flight service to tell them going to loose all electrical power before clearing customs in yuma, so don't shoot as i do not have a rag on my hear or a big beard. anyway after landing (pumped the gear down) the battery was dead. found out that both dioades were bad, not surprising they are almost 30yr old.

qalternator
 

73p has 60 amp alternators. my digital due hicky says amp/avolts. sometimes my discharge light blinks. chk my meter and it appears to be balance alternator isolated it is working fine . digital meters are sometimes better than idiot lights.

Jch

alternator
 

For what its worth! My bird is a 1975 P337G Riley. Just replaced the alternator driver coupling on rear engine. It was not in use for about five weeks. Started the rear engine and still had alternator light out on. Checked all wire hook ups to the alternator. All okay. Checked Voltage reg. and it tested okay. Checked fuse on firewall. Looked good. I took the fuse out and it was okay however had slight buildup of dirt and crud. Cleaned both ends of the fuse with wire brush and cleaned the saddle the fuse sits in. Yep! Everything works fine now. Message, don't over look the small things.
Jerry
N34EC

alt not working
 

hi, just went through this with a seneca lll. found the fues braker was bad and not letting current through. check the field post at the alt. if you are showing about 1.5v , this may save some time.check the pop out breaker and see if there is 24v on the hot side, then check the lead side and see what you are reading on the volt meter.

thanks
rick

Well, I have a great deal of text saved off on the subject, the bulk of it from GMAS on the other forum, some from others, including good stuff from Bob Cook and one from Bob on this forum (same as the link above). I tried to paste it in here but it wasw 147,000 some odd size and the message limit is 10,000.

So if anyone wants to give me an email address I'll mail the text to them.

Paul, I would very much like to have a copy of your material on alternators/electrical system.

Your profile indicates you don't wish to receive email, so I am responding to your thread.

My email address is : gjhumphrey@comcast.net

Thanks,

Gordon Humphrey

I don't give out my email much - sorry, but you know how that stuff gets to be all the time. Currently about to change it as I've been getting about 200 junk emails every day.

Anyway, I'm sending the text to your email address. It's a pretty good list of things to check, ideas, etc. Hope you find it helpful.

not only did age kill the diodes, but the front alt. coupl. broke, it would charge up to about 22v then blead back down (i'm assuning as it took on loads the coupling would give away(??)). may have been defective for a long time as i was always cycling the alt switches. is there any reason these coupling fail (new alts 150. ago)