Alternator overcharging, bad regulator?

12V conversion on Dad's W-400.

The alternator is putting out 17.5V to the battery any time the tractor is at more than an idle.

That means the regulator is no good in the alternator right?

Alternator is a brand new Delco 3-wire, wired up per a printout of Bob M's diagram.

Assuming the #2 terminal is connected to the Output stud, (and has good conduction) the regulator is probably bad. The testers at the store often do not evaluate high output very well. Jim

If you are reading the output of an alternator with a digital meter, find yourself an old analog meter and try that. The output may not be as much as you think. I have found digitals do not read correctly on the output of some alternators. The output is not a steady DC like it is from a generator, but a 1/2 sine wave.
If you are already reading with an analog, forget what I wrote.

Is the battery over-boiling?

If so, I'd be for checking for a sulfated battery(s). Perhaps the regulator is just trying to do it's job.

'Sides, some of those tractor applications run the regulator at 16.5V anyhow.

Allan

Seems to me that if you're seeing a 1/2 sine wave, that would indicate the regulator and regulation is bad.
But you can't see a 1/2 sine wave with either an analog or digital meter. Need an oscilloscope.

This had been a regular problem with the regulators in the last 10 or 12 years or so. It was extremely rare like 30 years ago. The number two terminal must have a good tight connection or it can cause this problem also. In reality, the number two connectiion should have a wire running all the way back to the first heavy battery cable connection not on the battery. This will give regulator a much better sense how to regulate. Most of us just hook conversions to the large output terminal at the alternator and get by most of the time. All original wiring harness's the sense lead came from right near battery to reduce error causes by voltage drop in output wire to battery during heavy charge periods. I put three regulators in a alternator one day, and then finally replaced alternator to cure problem. Also, put about four in another one along with all different parts, including rotor, except the stator which I did not have a new one or good used one and then I replaced the whole alternator. Fact is, I even isolated the alternator from all other wiring on tractor by running it to a spare battery and just using the tractor to run the alternator. Now this alt has been on for about four years.

I would have the alternator checked at your local
shop that repairs generators, starters and alternators. Probably has a defective regulator. Hal

Suggestions already offered are all good. But here's another quick check before getting in too deep:

Look at the back of the alternator - make sure the regulator shorting tab (the small ear inside the D-shaped opening in the photo) is clear. If it is bent, or there is anything conductive caught on it so the tab is grounding to the case, the regulator is bypassed which causes the alternator output to "run wild".

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To Allan in NE: With due respect, there is NO tractor application (or any application for that matter...) with a design voltage of 16.5 volts. Running a 12 volts system constantly above 15.0 volts will destroy the battery in short order. It also dramatically shortens life of incandescent lamps.

All the above, plus, make sure the #2 "sense" wire in the alternator plug is connected to full battery voltage. If there is no connection or a poor connection between the #2 sense wire and battery voltage the alternator may charge flat out,18+ volts. BOB from ND tells me the original delco SI regular would default to about 1 volt above normal if the #2 sense wire sees no or low voltage, but I have seen aftermarket regulators that will charge "flat out" of they lose the #2 sense connection.

On A tractor where the alternator is exposed to weather, remove the regulator plug and inspect the flat regulator blades for rust. For some reason, most / all regulator blades are unplated steel and will get rusty. Clean those blades shiny and push a bit of electrical grease in the plug terminals to prevent more rusting.

I have had several SI series Delco's on tractors that charged flat out" because the #2"sense" blade became rusty and lost connection to the plug.

Also do not trust the volt reading from a digital meter, as an electrically noisy system will confuse a DVM and make it read high. A battery load tester has a big analog meter that when connected to the battery posts, will give an accurate charging voltage reading.

A missing or broken insulator on one of the regulator mounting screw inside the alternator can also cause the alternator to produce full output all the time. It has the same affect as shorting the test tab to ground.

We're wired up per Bob M's diagram, #2 to the BAT post on the alternator.

Analog meter too, so I know we're getting an accurate reading of voltage. Plus the ammeter is PEGGED...

I'll check the test tab, but we already pulled the alternator off the tractor to take it back.