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Alternator Question

Geeman

Well Known Member
I am starting my annual and the last few flights I noticed my amp meter oscillating. Thought I may need a new alternator and or a regulator. This is the alternator I have. Anyone recognize it? Also a picture on my firewall. Thought this may be a regulator..not sure. Any help appreciated.

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looks like

the regulator (Ford and a good model) is not hooked up. The alternator is a common one and you can easily take the brushes out and replace. They last forever in a car and only 2 or 3 years in a plane. A good alternator shop can replace the brushes in 30 minutes or less for $30. That alternator was made with internal regulator which often fails after the brushes get worn down. I personally think the many guys that say those alternators rarely fail, fly low and slow. The higher and the longer your flight legs the faster the little alternators fail, imho.
 
Your saying that is a regulator on the firewall?

Yes, that is a regulator common with mid-70's Ford cars/trucks and often used by those of us flying with the small Nippon Denso externally regulated alternators.

Your plane probably had one of those alternators but was later changed to the internally regulated unit and the field lead was disconnected from the regulator. It is now dead weight. The lead attached to the 'A' terminal should be 12vdc coming from the aircraft bus (via a breaker)....but it may have been disconnected at the panel as well.
 
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If the bearings in the alternator are good and it's not making noise on your electrical system, chances are good that replacing the brushes as Dale suggested will bring it back to 100%.

It's a simple and inexpensive thing to try, anyway.
 
I personally think the many guys that say those alternators rarely fail, fly low and slow. The higher and the longer your flight legs the faster the little alternators fail, imho.

Well Dale, you are entitled to your opinion of course, but I fly long, high, fast legs, criss-crossing the country many times, and have gotten very long life out of the stock ND internally-regulated alternators. The key I have found (empirically) is to keep the reg cool with a blast tube and make sure you get a good alignment on the alternator - and it will last a very long time (defined as 1000+ hours....far better than I ever got on a certified alternator in a certified airplane).

Paul
 
More help.

Forgive my ignorance but I am not familiar with wiring up regulators. But if I have an alternator with an internal regulator and I only have one big wire going to it, is the internal regulator regulating? Anyone have a simple wiring diagram of how this is suppose to be wired? Do I need that firewall mounted regulator. Maybe something is not wired correctly causing it to oscillate.
 
The regulator on your firewall is a Ford-type regulator that you can get at any auto parts store. It would be wired like this:

Ford Regulator Wiring Link

Since the "F" field wire does not go to the alternator, the regulator on the firewall cannot possibly be controlling the alternator. So the conclusion is you probably have an internally-regulated alternator, and the previous owner who did the alternator swap simply left the unused wiring and regulator in place.

It is possible, though not necessarily optimal, to wire a self-exciting, internally regulated alternator with simply one big wire to the battery. This sounds like the setup you currently have.

Read About 1-Wire Installation Here

If you've had good operation from the alternator in the past and it recently started acting up, a simple brush replacement would be the first thing I'd try. When the brushes get worn they stop making perfect contact with the rotor, and the regulator can't do its job properly.
 
Anyone recognize this alternator

No part numbers on it that I can find. Thinking about just buying a new one.
 
No part numbers on it that I can find. Thinking about just buying a new one.

Most don't have part numbers on them. Look for an alternator/starter repair shop in your local area. They'll test the alternator for you and determine whether the internal regulator is going haywire or if a brush replacement is in order.

If it's brushes, they will be very familiar with the process and likely have parts on hand for your alternator. Watch them do it and then also buy a couple spare brush sets from them at the same time. It's easy and cheap.
 
It looks like a typical Denso Mini alternator. If it is, then everything is serviced from the back cover. You can take the brushes out thru the back with out splitting the alternator case.
I have one that failed to make voltage after a few hours in service. The plastic boxes that hold the brushes were too tight, the brushes wore a bit and lost contact with the slip rings. The Rebuilder (his actual buisness name) sold me new brush boxes for $6.
Gotta love that Mini Denso...
About alternator service life: The high RPM caused by the pulley ratio shortens the brush & bearing life. I think full alternator output is @ 6000 RPM.
I measured a Denso alternator pulley a few days ago, if I recall correctly, it was about 2.75". Used with a 9.75" Lycoming pulley:
9.75 / 2.75 = 3.54:1
3.54 x 2700 = 9572 Alternator RPM
Canton Racing makes a 3.25" pulley for the 15MM shaft Denso and other metric alternators.
https://www.cantonracingproducts.co...DIA-V-BELT-ALTERNATOR-PULLEY-WITH-15MM-SHAFT/
Lycoming flywheels are made with 9 3/4" or 7 1/2" pulleys.
9.75 / 3.25 = 3:1
3 x 2700 = 8100 Alternator RPM
7.5 / 3.25= 2.3:1
2.3:1 x 2700 = 6230 Alternator RPM
I have 7 1/2" on my O-360. I feel inclined to try the Canton pulley, the alternator RPM would be right in the sweet spot for flight, although output might be low during ground operations.
 
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Bad overhaul broken at Osh.

Well I sent this to a local alternator shop and they must have muffed it. On the way to Osh the amp meter started over amping bad and got the smell of burning wire. Tuned off the alternator master and killed the smell and over amping. Landed at next airport, pulled the cowl to make sure there was not a wire rubbing , arcing, etc. everything looked fine. All I can figure is the shop screwed it up. Now I'm at Osh needing an alternator. Going to plane power booth in morning, if they have one to see if I can get a new one. If anyone has the style shown in picture I would gladly pay for one to get me home. Or any suggestions to getting one on at Oshkosh.

Thanks
Kyle Gee 281-455-6784
 
If you just want to fix what you have, a trip to an automotive store will get you parts. There is an Auto Zone and Advance Auto in town.
 
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