[prairieschooner]

Have you put any penetrating oil on the screw to loosen it up? Looks to me like that is the adjustment screw, but God and elaine know I have been wrong before. In my more impatient days I would have just started turning the screw until it stripped out, or sheared off....

Not so sure that Penetrating Oil would be good on an Electrical Component like that Regulator.


Tom, follow this link;
http://www.prestolite.com/pgs_support/tr...hoot_1.php

and this one;
http://www.autoshop101.com/forms/h8.pdf

[encantotom]

the screw was not hard to get out. i was at first thinking the cap was the adjustment screw and i thought it was hard to adjust. it came right out once i realized it was just a cap.

tom

[Fulltiming]

If you weren't having problems with your batteries running down it isn't likely an issue but you might try checking for bad diodes by checking for AC output on the alternator output lines. You may have also built up resistance in the grounds and battery contacts.

[rheavn]

I just got done dealing with a low voltage issue with my alternator that had just been rebuilt last December. I was only showing 9.9 volts at the center post on the battery isolator. My starting batteries were 8 years old so I replaced them even though they started the coach. Then I cleaned all the ground connections from the batteries to the alternator. I was still getting low voltage. Took the alternator back to the rebuilder. He said the positive brush looked brand new, but the negative brush was burnt down to 1/4". He said the only thing that would cause that brush to burn was either a shorted battery and/or dirty ground circuit. I'm guessing one of my starting batteries was shorted. Put the alternator back on & I am now getting 14.4 volts at the battery isolator.

[RussWhite]

I guess we are all entitled to our opinions here, so this is mine....

Field current is supplied to an alternator through brushes riding on slip rings. The more current that is supplied, the more voltage the alternator produces at the same rpm. It is the job of the voltage regulator to determine how much current to send through the field to produce the appropriate voltage.
The field circuit is a series circuit. In other words, the current that goes into the field coil is the same current that comes out the field coil. That current goes in through one brush and returns through the other brush. Much like a battery, the current that leave one pole returns through the other. You open a battery on either positive or negative side, all current stops. Same with the field current. You have one bad brush not making contact, all current to the field is stopped and the alternator will not produce.
So my opinion is, when the one brush became worn to the point of no contact, your alternator stopped producing the correct voltage. This happened because one brush was not replaced when the alternator was rebuilt. The story was fabricated by the builder to cover his mistake. Brushes wear at the same rate as they have the same current going through each all the time. That's my theory. In any event, you should be fine now with good brushes on both poles.

[encantotom]

ok russ, what say ye about my situation?

tom

[rheavn]

Russ,
Thank you for your reply. I never take your opinions lightly on electrical issues and will put it in my mental file. I will tell you my rebuilder is a pretty reputable shop that has been in business for 35 years. The rebuild was done by the owner who I have gotten to know. My receipt did show that all brushes & bearings were replaced back in December.

[RussWhite]

I would be concerned given what you have told us. On the surface it sounds as if you had to make a large adjustment. I would want to understand why before I could just move on and forget about my alternator.
I'll ramble on a bit since you asked. Your regulator is not integrated, but it is functionally the same. It gets a battery voltage signal from somewhere and then uses another battery voltage circuit to supply field current. The "sense" terminal normally draws very little current so the voltage drop on that circuit is low so the regulator is able to "sense" the actual voltage at the battery. That is the voltage the alternator needs to get exactly correct. My alternator with its integrated regulator has a "sense" wire, a D+ which supplies the field current, and then the huge output wire that actually charges the battery as well as makes up for usage while you travel.
So the question becomes, why was your voltage too low? If it were me I would at least check the actual voltage across my battery at the poles against what the VMSpc is showing. I suspect they will be very close, but I would want to be sure from the start I am using a voltage signal for the adjustment that is right on. That's why I keep a 4 1/2 digit fluke that has been tested on a calibration source regularly.
Now you have to ask yourself, is this a new situation, or did you inherit it with the coach? If it's been there a long time maybe it is something just as simple as the regulator was never adjusted properly as the PO just wasn't watching that closely. But, if it has changed in the time you have had it, then an answer for why is needed.
The voltage at the batteries ( and we will assume for now shown on the VMSpc ) may not be what your would measure at the output of the alternator. That would be one of the first things I would check. Any significant voltage difference could be a reason for your having to adjust the regulator. The difference would likely be caused by unusually high resistance in either or both of the circuits between the alternator and the starting batteries - ie. ground connections, terminal corrosion, terminal tightness, physical damage to any wires, etc.
The other main area I would suspect is that for some reason the same field current that once produced the correct charging voltage is now requiring more current to produce the same voltage. The normal culprit there is a failed diode, or even more than one. The rms value of the voltage will decrease with any diode failure. This will also produce a higher ripple voltage that you may be able to measure using the AC setting on a DVM. A scope or scope meter would allow you to look at the actual pattern of the waveform. Sorry I don't know exactly what AC voltage would be alarming. I think I will take some reading on my "new" alternator and just store them for future reference should something like this arise in the future. I have heard folks say that a failed diode will increase the RF noise generated by the alternator and will sometimes causing buzzing in the radio or CB. Hope I have give you some things to think about and check. Russ

[encantotom]

thanks russ, i will contemplate it.

it has been essentially like this since i got it i believe.

once i put the vmspc on it has varied between 12.9 and 13.1 from the time i got it.

my batteries are new. i replaced a few of the cables in there due to corrosion and cleaned up the rest.

i will check some more, but it seems like they are ok.

the gauge on the dash is pretty close to what the vmspc reads and has read.

tom

[encantotom]

ok, being the curious soul i am. i went out and ran it for 15 minutes or so again at high idle with the lights on bright and the dash fans on.

it started out at 13.8v just like before, but after a while crept back down to 13.2 volts or so. even dipping once down to 12.9.

this is measured at the vmps pc gauge, so i was not on the batteries. i will do that next time.

something still isnt right.

tom