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Old 12-29-2016, 08:20 PM   #1
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Charging System Issue on 84 Chieftain

I am really stumped and could use some help.
My son recently purchased an 85 Winnebago Chieftain, with a GM 454. It is not charging the batteries.
With the engine running, I'm showing only about 12 volts at the batteries, same with engine shut off. So obviously not charging.

I then checked for voltage right at the alternator. Same 12 voltes at the larger lug with #10 wire going to it. I checked the plug connector going into the body of the alternator. With key off, no power to either side of the plug. With ignition on, 12v to both sides on the plug.

So......since this alternator appears to be one with a built in regulator (this could be my mistake) I am left with assuming the problem is the alternator.

But, when I physically remove the alternator and take it in to be tested, they say it's fine, putting out over 14v.

Take it back, install and same problem.

All I can think of is that there really is an external voltage regulator, or that somehow there is a problem in an isolator somewhere.

Anyone have any experience of thoughts? I'm just scratching my head at this point.

Thanks

toni
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Old 12-29-2016, 08:43 PM   #2
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You may have an old fashion dual battery isolator , that won't pass power to the batteries.
The internal regulator in the alternator , controls output by looking at resistance to charge in the batteries , if the isolator has high resistance then the regulator thinks the batteries are fully charged and cuts output.
You could test this in the vehicle by connecting a HEAVY gauge wire or jumper cables from the alternator stud to the chassis battery directly to see if the charge rate goes up.
Your vintage isolator may look like the blue box in the picture below.
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Old 12-29-2016, 10:15 PM   #3
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You may have an old fashion dual battery isolator , that won't pass power to the batteries.
The internal regulator in the alternator , controls output by looking at resistance to charge in the batteries , if the isolator has high resistance then the regulator thinks the batteries are fully charged and cuts output.
You could test this in the vehicle by connecting a HEAVY gauge wire or jumper cables from the alternator stud to the chassis battery directly to see if the charge rate goes up.
Your vintage isolator may look like the blue box in the picture below.
thanks so much skip. I'll check on it tomorrow. Really appreciate the help.
toni
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Old 12-29-2016, 10:52 PM   #4
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Does the alternator have a spade lug, 1/4", with an F stamped near it? Is there a wire there, or is it missing? If there's a wire there, does it have 12 volt on it when the key is on?

Many RVs of that era, had a Field voltage (aka 'excitation voltage') that came from the dash. There was a diode in series with that wire. If any of the connections to that F terminal are corroded or missing, or if that diode is bad, you'll get that symptom of having a good alternator but it not putting out anything over 12V.
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Old 12-30-2016, 01:47 AM   #5
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See if you can tell what model alternator it is. A few pictures could also help.

If you have battery voltage at the large terminal, it wouldnt have a diode isoator. They block the current from comming back that way.
It could be there but someone messed with the wiring. Have you checked if the house batteries are charging while running ?

Did you check voltage at the large terminal while running the engine ? Maybe it's working but a connection down the line is opening under load.

Some of the old alternators need a rev up, on the engine, to kick in. Usually the single wire ones, but worth a try.
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Old 12-30-2016, 08:25 AM   #6
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Typically a GM 4 wire alternator will have the heavy 12V lead, an excitation, and sensor wire. The sensor wire should be hooked to the distribution point and should be hot all the time. The excitation would be only with key on. Your sentence below makes me think the wiring has been messed with. And your alternator is almost certainly internally regulated.
" I checked the plug connector going into the body of the alternator. With key off, no power to either side of the plug. With ignition on, 12v to both sides on the plug."
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Old 12-30-2016, 07:09 PM   #7
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Typically a GM 4 wire alternator will have the heavy 12V lead, an excitation, and sensor wire. The sensor wire should be hooked to the distribution point and should be hot all the time. The excitation would be only with key on. Your sentence below makes me think the wiring has been messed with. And your alternator is almost certainly internally regulated.
" I checked the plug connector going into the body of the alternator. With key off, no power to either side of the plug. With ignition on, 12v to both sides on the plug."
I got worried about no power to either the #1 or #2 (sensor?) wire. So I wired it direct to 12v, on all the time. The exiter wire is switch controlled and shows power. So as it sits now, I have 12v continuously to the #2 plug and switched 12v to the #1 plug. The 12v lead is obviously, 12 volt and measure the same as the battery, running or not. The alternator is a pretty much standard delco 12 SI. I will try and snap some pictures tomorrow. Thanks again.
toni
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Old 12-30-2016, 07:14 PM   #8
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See if you can tell what model alternator it is. A few pictures could also help.

If you have battery voltage at the large terminal, it wouldnt have a diode isoator. They block the current from comming back that way.
It could be there but someone messed with the wiring. Have you checked if the house batteries are charging while running ?

Did you check voltage at the large terminal while running the engine ? Maybe it's working but a connection down the line is opening under load.

Some of the old alternators need a rev up, on the engine, to kick in. Usually the single wire ones, but worth a try.
OK, its a 12 SI pretty much standard mid 80's alternator. I do have battery voltage at the large terminal and it does not change with engine running or not. I will double check, but do NOT believe the house batteries are charging when running. My house batteries are sitting with higher voltage, approx 12.8 but I'll double check when I start it up. I've run it in so many configurations now that I'm confusing myself. Tried revving it up...no love there. I do like the idea of a down stream connection being open. that's the difference with the darn motorhome, there is so much extra junk to account for.

thanks
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Old 12-30-2016, 07:19 PM   #9
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Does the alternator have a spade lug, 1/4", with an F stamped near it? Is there a wire there, or is it missing? If there's a wire there, does it have 12 volt on it when the key is on?

Many RVs of that era, had a Field voltage (aka 'excitation voltage') that came from the dash. There was a diode in series with that wire. If any of the connections to that F terminal are corroded or missing, or if that diode is bad, you'll get that symptom of having a good alternator but it not putting out anything over 12V.
Jim
I'm not sure about an F terminal. What I have is a 1/4" terminal that has about a #10 wire coming off, that shows battery voltage no matter what. In fact, there is a stamped "Bat" next to it. There is a smaller hole that has no lug or anything that has an R stamped it. Then there are the field and armature connectors, marked 1 and 2. Thats all I've got.

toni

thanks
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Old 12-30-2016, 07:20 PM   #10
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If it wasn't a MH, the alt wire would go to the + battery terminal on the starter motor. Simple.

Back then, they sometimes moved the output to something to split the output.
Some use solenoids and some used diode isolators. You need to follow the wires.

Here is some info on Delco alts.

http://www.madelectrical.com/electri...elcoremy.shtml
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Old 12-30-2016, 11:10 PM   #11
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Jim
I'm not sure about an F terminal. What I have is a 1/4" terminal that has about a #10 wire coming off, that shows battery voltage no matter what. In fact, there is a stamped "Bat" next to it. There is a smaller hole that has no lug or anything that has an R stamped it. Then there are the field and armature connectors, marked 1 and 2. Thats all I've got.

toni

thanks
It's the Field terminal that we're interested in. Check if there's a 1/4" terminal, female, hanging in the air somewhere near the alternator that's suppose to be connected there. If you follow that wire, and it's likely just a 16 ga wire, a couple feet from the alternator there will be a bump covered by heat shrink. That's the diode. Check the alternator side of that wire, it should have battery voltage (chassis battery level) on it when the key is on. If not, it's likely a bad diode. Fairly common failure. That voltage comes from the chassis battery, through the key switch, through one of the dash idiot lights, then back to the alternators 'F' terminal. That's the field voltage. With no, or low, field voltage, the spinning alternator will not output much. A burnt out idiot light bulb (alternator warning light) can cause the problem too.
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Old 01-29-2017, 05:27 PM   #12
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Here's an update. Still no love as far as the system working. But I've eliminated the alternator. Here is what happens.

If I completely isolate the charging system from the bus, the alternator charges. In other words, I've fun a jumper from a separate battery to the two terminals on the alternator, so those are not being energized through the wiring harness. Fire up the engine and the alternator puts out 14+ at the battery terminal on the back of the alternator. So, alternator works. But then, if I hook up the chassis wiring system in place of my jumper, voltage goes away...i.e. alternator not charging. Check the voltage on the field lead and its got 12+ volts. Something happens when I plug the system together that prevents the alternator from working.
So then, if I go back to my jumper wire instead of the wiring system, and then hook up the chassis lead to the battery terminal on the back of the alternator, again, no alternator output.

So it works if it is completely isolated, but if either there battery terminal or the field wire is hooked up as designed, it stops generating.
So, its something in the wiring harness of the bus. Haven't been able to chase it down yet.
This is frustrating with a capital F.
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Old 01-30-2017, 06:57 AM   #13
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Disconnect the 2 small leads at the alternator. Run a jumper from the alternator output to the sensor lead.
See if it charges.
Oh yeah, do you have a dash idiot light?
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