M923a2 Alternator confusion

[clint1]

Two weeks ago I noticed my the side maker lights became much brighter when I started the truck, I looked at the voltmeter on the dash and the needle was in the far right red. I shut the truck off to go get my DVOM to confirm my over charging fears, at 39 volts It did.
The next night I researched the tms to find not much about diagnosing the overcharging regulator.(TM 9-2320-272-23-1 WP0091)I unplugged the alternator wire 568 (ignition wire behind alternator)to stop charging while I brought the truck closer to the house to work on it.
I read on steel soldiers about adjusting the regulator, so I pursued that task of trying that I couldn't find the allen plug to remove to adjust the voltage so I took the regulator off to see what is was going on and to look for fried components. With the regulator off and grounded to the alternator with a jumper wire. I was able to adjust the regulator back to the proper voltage (28.5) with 568 plugged in. It seemed to stay there while during testing in the driveway but when I went to park it the voltmeter was back in the red and as everyone knows how sensitive the ABS ECU is the light was on with a blown 15a fuse. I tried clipping the protection diode to hear that magical sound of a self test with no luck.

I broke down and bought a voltage regulator and an ABS ECU. I put the new regulator on and adjusted it to 28.5v and everything seemed happy. I drove the truck to work the next day (15 miles) and took it to lunch (8 miles) with a sharp eye on the voltmeter. On the way home The voltmeter was back in the red, I pulled over with fear of killing my new ABS ECU and unplugged 568 and went home. I tried adjusting the voltage regulator (with 568 plugged in and ABS fuses pulled) and it was unable to make any voltage adjustments regardless of where the potentiometer was.

I have battery voltage on the harness side of 568 and low voltage drop(<50mv i think)on the ground side. Before I put the new regulator I isolated the batteries and checked for dead cells and found nothing. I think the new regulator is dead but I am afraid of throwing more parts at it. I think there is a broken wire somewhere that I am missing because the problem seems to randomly reappear.

Sorry for being so long winded but I wanted to tell the whole story with the hopes of someone having a problem like this so I can get to the bottom of this.

I attached a photo of my original regulator so other people that would be like me that couldn't find the allen plug on the bottom of the alternator can see where the philips head voltage adjustment pot is without taking the voltage regulator off.


Thanks

 

[dmetalmiki]

( Before going/spending further) That would seem to call for a proper test with the correct equiptment set up at a decent auto electricians shop. ( As I recall alternators rely on those "electrical gizmos" to regulate <bemf> which if not controled (stable) the output "runs away" without regulation. I have a really good "old school" re-builder with all the old and new equiptment testers only 3 miles from where I sit now..perhaps you know of someone similar?. Good luck keep us posted with the diagnosis and remedy.
Take both units to the ( chosen) facility. Perhaps an auto electrician among our members can clarrify further. (better)

 

[74M35A2]

It is not alternator confusion. These factory alternators just flat out suck. This forum has numerous active threads on it even right now of alternator problems, just on page one! Ugh. I do have a stock one working on my truck, but it seems they are so picky about any disturbances in the system. Even dead or discharged batteries can execute a stock alternator at extended idle. That is the most difficult situation because RPM is low, so cooling airflow through the single alternator fan is also low, and load is high. Maybe that was the best they had back then, but we're a lot better now.

A step up is to buy the Cummins J-180 short upper alternator bracket. Part number in another thread, and about $90 new, $10 used. That will enable one to properly fit easily obtainable civilian alternators on their engine. You can fit a J-180 short alternator onto a J-180 long bracket, but it is kind of a shade tree configuration. It can work though.

The J-180 short alternator is widely available in 24v for US off-road applications. Most rebuild shops will have them or can build one up for you. Request a name brand one if available. A member here just had one built up with warranty for $130. China is flooding the market right now with new $100 Delco clone alternators. Some work, some work only briefly, and some don't work at all.

To answer above, the alternator regulator is a very simplistic electronic device. It is just a single switch, which is a FET (transistor), and it quickly turns current on and off to the alternator rotor, based upon if the measured voltage is above or below the preset value in the regulator. This is the power that goes through the brushes, and creates a rotating magnetic field that cuts through the outer windings of the stator. The FET constantly switching on and off creates heat, and eventual destruction of the regulator itself in low cost alternators. This FET can fail in the on or off position. It takes high temp electronics with good heat sinks and good airflow to make a robust alternator.

The real power is developed in the stator windings as AC current. There is a diode pack on the rear of the alternator that is known as the rectifier. This essentially blocks half of the AC wave and allows only DC power to leave the alternator.

I am working on a path to offer brand new 130 amp 24v alternators. They are name brand and not Chinese. They are compact, J-180 short, internally regulated with temperature compensated voltage regulation (higher charging voltage in winter), twin internal fan, with pulley, and 3 year warranty. They will not commit suicide from charging low batteries.

 

[clint1]

It would seem to me that alternator is still working because of the output, just the regulator died again. What killed it seems to be the mystery though. Can the FET transistor be tested to prove that is the problem? Now that you mention the diode pack I will go check the ripple voltage to make sure those are tight.

Another idea I had was to use an external regulator to control the voltage.

74M35a2 is do you have a link for the alternator you speak of handy? If that could be an option I would be willing to try it.
Is the top bracket the only thing that needs to change for the 21si alternator or does the bottom need to change also ?

I just discovered I have a new CAT reman 26SI on the shelf that is 50a, tomorrow I will do some measuring.

 

[joesco]

IMHO, the stock regulator / generator caused my truck numerous electrical issues. I've since upgraded to a one-wire alternator sold by one of the SS vendors. The kit included brackets and was a snap to install. I now have nice clean charging power and about 20% more amps than the OEM unit.