Alt. Charge light

[H. Miller]

Not sure this is a Monaco or Cummins 8.3 question but here goes:
Upon start yesterday (first start in a month & 16 deg) the Alt. Charge didn't go out. The voltage guage read 12.5 volts and wouldn't increase much at all with a little more rpm's.
Pulled the MH from barn to house and restarted an hour later - no light and volts @ 14.... Drove a couple of hours with no problem. At destination the engine was shut down but needed to restart for slight repositioning. Yep, Alt. Charge light was on and 12'ish volts. By now it's 50 deg.
Any observations?

[GWCowgill]

Hal,
I would start by checking the belt, you didn't say if there was any noise when the charge light was on, also alternators generally use a exciter voltage to start the alternator charging which may a simple 2 wire pug on the alternator to a screw post on the back of the alternator which needs to be checked. You dinot say the type of alternator so I am not sure what setup you have. There could be other problems such as a bad charge relay on some systems. Good Luck in finding the problem.

[GWCowgill]

I forgot to mention that your symptom sounds more like a slipping belt because of the heavl load at startup.

[Mike Canter]

When alternators or generators are stored for a period of time it is possible that the brushes in the brush block get a little corroded and stick so no output. Usually if the belt is slipping the alternator light will fade in an out and the voltage will move up and down when the motor is revved up a little. The best thing to do is check that the belt is tight and if it is then either you or somebody take the alternator off and take it in to a good alternator/starter rebuild shop and have them check or replace the brush block. As a warning here...if removing the alternator then first disconnect the chassis battery's negative cable and then be real careful when taking off the heavy red cable off the alternator that you do not turn the whole screw that goes into the alternator because that will screw it up the inside of the alternator for sure. Also the same thing when putting that heavy wire back on to the alternator. Do not overtighten and turn the whole screw but it has to be tight because of the high current draw. On most alternators you can use a special thin wrench to slip in under the wire to hold the backup nut. If you don't have one then buy one from Sears or somewhere.

[H. Miller]

This AM was preparing to leave the RV park. Had to start twice for a short time - Alt charge light both times with volts at 12.5. The third time (to leave) no warning light and 14+ volts!!! The serpentine belt is not slipping. Not sure it could be exciter volts missing as there is 12.5 volts with the Alt light on.
Appears to be something that will not allow volts to go from 12.5 to 14.5.
With engine running, where does volt meter get it's reading? If alternator is zero would it read battery volts?
It worked the entire 3 hour trip home!
Hal

[Mike Canter]

Hal, my guess is the brushes where stuck in the block or there was corrosion on the comutator. I say that since it worked for three hours and you saw 14.5 volts it may have fixed itself. The other option is like I said to take the alternator into a alternator/starter rebuild shop and get just the brush block replaced. The rest of the alternator is low mileage and should be OK. If you are mechanical or have a friend that is maybe you can swap out the brush block yourself.

[tinman1]

I may have overlooked this, however, were you connected to power source when you started engine and received the alternator light.
I had similar experience and have since noticed that when I start engine (while not connected to power source) the alternator light does not turn "on".
It might be worth a try.

[Poltax]

One other item to check would be the connections on your alternator. Double check to make sure they are not corroded or loose.

[H. Miller]

Originally Posted by Mike Canter

If you are mechanical maybe you can swap out the brush block yourself.

Does building an aircraft out of a box of parts count?

Later yesterday went out to put it in the barn - got alt. light and 12 volts! The motor was still @ 120 degrees and 75 deg. outside.
All starts have been while unplugged from any power source. Will get out the creeper today and check wiring.

[raptor9]

I also had my alt light come on after I did an oil change and was connected to power. Once I disconnected from power the light went off. I am not sure why it did this. But no problems since.

[H. Miller]

Problem solved!!!!!
Put 12 ton (each) jack stands under rear - get out creeper and find that alternator is 3 miles up into engine bay
Into MH and took out the closet floor - there it was, the alternator. All wires tight, nothing looks amiss. What's this? Hmmmm. Black plastic "box" about the size of a cigarette pack except only 1/2" thick and has wires (4) coming from it. It's tied to the wires coming out of the alternator and looks like it comes apart. It does come apart!!!!! And there are two 5 amp fuses inside - AND - one is blown. Send DW to auto parts store (it's her 41st wedding anniversary but she might as well be working if I am) and upon return and insertion of the new fuse - as stated above - PROBLEM SOLVED!
As Monaco electrical diagrams were of no help, I'm gonna guess the 2 fuses were for the "field" voltages. One field will put out 14+ volts but only 1/2 the 160 amps. Coach system would not come on line as the "cold starts" had done a number on the batteries and they were calling for more amps than the alternator was putting out.
BTW - The 12.5 volt reading when alt. charge light was illuminated was battery voltage.
Moral of the story: When Monaco says in their owners manuals that the alternator is not to be considered a battery charger - believe it!

[Mike Canter]

Thats a little confusing because a blown fuse is a blown fuse and not an Intermittent fault. So how come it would work sometimes and not others. Well as long as its fixed who cares. Great job on fixing it. Carry some spare fuses.

[H. Miller]

Originally Posted by Mike Canter

Thats a little confusing because a blown fuse is a blown fuse and not an Intermittent fault. So how come it would work sometimes and not others. Well as long as its fixed who cares. Great job on fixing it. Carry some spare fuses.

I can only think that possibly there is an overload protector that will not allow the alternator to come "on line" if the load is more than output. It seemed to be temp. sensitive which it may well have been. As the batteries warmed (nights were 20's - days were 70's) they became less of a load to converter/charger and allowed the system to come on line all of which could account for an intermittent condition.
As to fuses - I have box upon box of fuses BUT these would have to be classed as sub-sub miniature in size no more than 1/2X1/2" blade type.

[GWCowgill]

Had the same thing happen on my Dodge with the Cummins. Glad you found it and got it fixed.