I run a 3 wire 12 SI alternator that I spin backwards in my hot rod.

Saturday at Gainesville the car began to blow fuses on the ignition circuit in the ARC switch panel. This morning I was able to isolate the problem to a break in the F terminal wire. The rectifier was toast as was the diode trio. The regulator was gone too.

My question is this: will an open field wire cause this damage by feeding the voltage back through the ignition?

Very possible if Dio trio and regulator went south. More likely than not the output exceeded 15.8 volts. What do the stator windings look like ok?

quote:

Originally posted by TD3550:
Very possible if Dio trio and regulator went south. More likely than not the output exceeded 15.8 volts. What do the stator windings look like ok?

The stator winding were good. this was a Powermaster alternator. The stator and case are all that remain of it. The rotor was new a couple of years ago. It went to 18 volts on the test stand after the rectifier and trio were installed. After the regulator was installed it was at 14.8 or 8, I could see that last digit very well.

This was the first time I'd see a failure like this.

It was more common place where as the regulator went out first causing the issue.As you know high voltage relates to heat. Test the battery also if you have a chance.Battery case show any signs of swelling? Back in the day,you would catch a distinct odor when the voltage was excessive.This an ARC 4?

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I have not yet re-tested the field wire for continuity yet. The heat index today is 105-110 here.

Anyway explain ARC 4 to me, please.

My guess is based on what you've posted is that the field wire became open causing the regulator to go to high voltage as it sensed no voltage. I'm sure the electronics are okay but, like you I'm curious about the batteries condition. They took a slow charge but, what will they do being put to the test?

I directing that heat as an overcharge condition
within the battery ETC. Indicators are ballooned cases. (sides). The ARC(4) was at replacing all the fuses on the ARC as a safety condition.

Once a battery electrolyte starts to boil, it damages the internal plates.(plate shred) Battery wants more amperage/voltage. Alt is in overdrive now. 12V batteries must maintain 2.1 volts per cell. The test we normally would do is a load test on the battery (Fully charged) Draw minn 200 amps with a carbon pile tester and watch the voltage drop. Minn average is 9.8 volts and stay stable.

The second test would be a sulfaton test. This test here determines the cell plates ability to maintain it power within the plates. When a battery is sulfated the coating on the plates drops off to the bottom. Sealed batteries are a different animal. You can't test each hole with a hydrometer.

I have a pair of NAPA 8472 batteries. I've used this type for years and just change every five years. I believe they are AGMs.

They came off the charger this morning and had 13.2 volts. We'll see what they have in the morning when I re-install the alternator and replace the "F" terminal wire.

Heat. It's a part of Florida and it's no doubt I abuse this electrical system badly.

There was a problem with the diode/resistor in the field wire, I can replace this with another diode, which I have. Or I can replace it with a light in my dash panel.

I've never completely understood the concept that a light is used in that circuit or a resistor/diode. Can someone explain that to me?

Are you talking about the wire wound resistor? If i can remember it is used in case of of voltage loss to keep the light bright. I could be wrong

AGE = CRS

No this resistor takes the place of the 10 Ohm resistance wire in the factory type harnesses.

Are there no single wire regulators for the 12SI?

The alternator lamp acts as a resistor, and only glows if the current flows one direction or the other (over / under charge). Battery voltage and output voltage should match. It's necessary in the old regulators to excite the circuit.

I get all my HD alternators from https://www.dbelectrical.com/. All HD truck and never had a defect/return.They have just about everything.

12SI single wire..

https://www.dbelectrical.com/p...xciting-turn-on.html

It's been a few weeks. After I rolled the car out of the trailer it started a couple of times after disconnecting the alternator then wouldn't start again. After inspecting the entire wire harness for breaks or shorts and cleaning every ground I could find I was at a loss. I checked the Grid's alert log and found that the last alert was a high battery voltage condition. I borrowed a known good 7720 Grid and 7730 Grid controller combo. Replacing one a time I discovered the Power Grid was no longer outputting voltage to the controller.

I'm not sure if the alternator short caused this or if it was just a coincidence but everything is working now as it should.

Glad you finally got it fixed. Along with excessive output. Heck in my 3500 dodge service truck, The darn bulbs in the dash were going out due to a bad alt.. It's like when you look at the what they call gauge lol. Ya it's in the green. But how green. You get what I'm saying.. Until you put a meter on it. My Snap Off VAT tester with the carbon pile has a Diode bar graph on the right side.The way i understand it the higher the value, the stronger the diode bleed.

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Me, too. It took me a while as I'm dealing with a minor medical issue. Some days I just didn't feel like working on it.