Alternator trouble shooting

[BruceMe]

I'm fixing a damaged aircraft. I can't get the alternator to work and I have never seen it working, it may just be broken. To pull the engine I had to pull the leads and I don't know that I've rewired correctly. This is the model;

http://www.autopartoo.com/oem/denso/0210006851bmq.html

It has a plug with three leads

E _
F| | N

E is Negative
F is Field
N is Stator

There is a small metal box on the alternator. It's already has a hard wired ground, and one red line in that goes hot when the alt switch is on and one green and a yellow line going out that I know went to two of the pins above. Which is which?!

I've tried wiring this in several configurations, but none appear to make current.

Where do I start diagnosing this? What is the little metal box doing?

[BillL]

A picture would help. That link shows as an externally mounted regulator.

Look at this diagram on the B&C website. http://www.bandc.aero/pdfs/lr2.pdf

This might be a start.

[BruceMe]

The red wire is definitely coming from the alt switch. Neither the yellow or green line go high when that red line goes high.

[BruceMe]

I suspect the steel box is the regulator. It's probably a cheap automotive thing. As the output doesn't run through any other boxes; clearly it can't directly rectify or regulate the output, rather it uses the stator/field feedback to directly manage the field output voltage to match the system + 1 ~ 2v. There must be a bridge rectifier in the alternator. I know just enough electronics and induction to get myself in trouble here.

[BruceMe]

So after even more research... I think I have an "external regulator". It's job is to supply a current from the field to the stator. That energizes the main coils and supplies the working current. It is likely the alternator is internally regulated. The red line is the "on", by common standards, the yellow line should be "stator" and green is "field".

I'll wire it as such and test and let you all know tomorrow.

Thanks!

[BillL]

Originally Posted by BruceMe

So after even more research... I think I have an "external regulator". It's job is to supply a current from the field to the stator. That energizes the main coils and supplies the working current. It is likely the alternator is internally regulated. The red line is the "on", by common standards, the yellow line should be "stator" and green is "field".

I'll wire it as such and test and let you all know tomorrow.

Thanks!

Bruce, it is definitely externally regulated. The small box is likely a transpo brand regulator. This is a very early Denso alternator and even the alt repair guys sell an adapter for that plug. The red wire is the voltage supply to the regulator. The only question it seems is the location of the green/yellow connections to the alternator. Is that right? If so, you might consult a local alternator shop. They are rare, but contact the local truck repair shop, they will send truck alternators/starters for repair often. They shop guys should be able to help if they have some gray hairs, and experience with the older hardware.

Good luck, let us know how it works.

[lr172]

That little regulator will need 12VDC (from somewhere other than the alternator - the B lead should work, but should be coming from a Field switch in your plane) a ground and then an output to the Alt field (F spade). Nothing connects to the N spade). Assuming the alternator is properly grounded, it can pick up the ground from the E spade. Don't know enough about the guts of that VR to be able to tell you whether the yellow or the green is field vs ground. A betting man would go with green=ground as that is a pretty standard electrical color convention, at least in the AC world. I am not a EE, so cannot give you a test procedure to determine which is which. However, I would speculate that the ground would have 0 - .5 ohm resistance to case and the field would be either a higher resistance or open.

EDIT: re-read your post. I am guessing that the hard ground is bridged to one of the two wires and is designed to bring the ground to the Alt via the E spade. A VOM should tell you which one it is.

It also looks like you have a Capacitor on the 12VDC feed. THese are used for noise reduction. You should test this to be sure it hasn't failed.
Larry

[BruceMe]

I don't have an amp meter that can read 30A, but I wired it up as I said, and I _THINK_ it's working. At 1700 RPM I flipped the AMP switch and the voltage rose above the voltage before I started.

I'll do more tests and a solid flight will tell me for sure.

Thanks All!