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Old 01-06-2019, 10:34 AM   #1
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3rd alternator...why?

looking for some advise and help.

im about to relace my alternator. this makes it number 3 in probably less than 3 thousand road miles.

maybe i have a phantom short and i have chased that some to no avail.

i need to charge my batteries to start my rig, almost every time. the batteries are dated 3/15.

when im driving.... the volt meter goes crazy, flopping all over the place. from 8-13 every second or so. the ammeter shows it pegged to the charging side and it doesnt move.

i've had belt issuses and just changed the belt and water pump and alternator - 2 years ago? only a few thousand miles since that.

im checking connections today, but what anything elseshould i check ? before i pull the alt and get another?

the battery looks like it could start it today, but by tomorrow the volts will be under 12.
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Old 01-06-2019, 11:28 AM   #2
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well I don't think your problem is alternator.

You may have more than one problem. All of your problem could be caused by just one thing.

Diagnose the problem first, then decide how to repair the problem.

First question I would pose, "how is the out put of the alternator wired to the batteries?"

Second question, "What is turning off and on?" I believe that is the source of the 8 to 13 volt. Could be the gauge is wrong. So, wire in a different volt gauge for a temporary volt meter.

run two tests, volt meter/gauge on the out put of alternator and negative terminal of battery. second test voltmeter on positive post of battery and negative post of battery. do the above with engine off and engine running.

this is just the start of the diagnostic procedure.

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Old 01-06-2019, 11:52 AM   #3
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thanks for the help!

1st off, its an all mechanical '93. for day time running all i need is the blinkers and they worked fine yesterday.

i have a second battery meter other than the dashboard gauge. i have a pair of aftermarket battery meters installed on my truck batteries - one for the vehicle side, and one for the house side. the truck side voltmeter confirms the dash readings. its a digital meter and an alarm comes on at around 9 volts. that alarm was ringing yesterday as i drove.

it didnt start out that way. the first 20 miles was fine and normal. the rest of the 50 mile trip the alternator was funny. i didnt dare turn the bus off.

my last issue with with a belt that i think was too tight. i had to replace the water pump then too, as the bearings of it and the alternator were gone. they wobbled. i have loosened the belt and i don't detect any wobble in the alt. i have tried hard enough to check the water pump. its cold outside.

the alternator connections look secure. there is a ground connection, positive post and a smaller control wire.

i'll get it started and try the test. thanks
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Old 01-06-2019, 01:46 PM   #4
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have you checked the voltage regulator? -
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Old 01-06-2019, 03:21 PM   #5
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Couple more suggestions turf,


Yes, the belt could be too tight if it's tearing bearings out of the water pump also.



Do your guages differ if you change rpm?



Check voltage at alternator at 2000rpm as well as on either fast or slow idle.




But first, if the alternator was changed, does its pulley lineup with all other pulleys when replaced? Same for the water pump.
The tightness might be fine but the pulleys aren't lined up even.


Just one off like this will rip it apart too.



A good steel straight edge might tell you how close pulley alignment is.

Very critical to belts and components.



Seems like you know how to test so good luck and keep us updated.




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Old 01-06-2019, 03:54 PM   #6
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hey again.

im trying to recreate the issue, so i'm sitting here waiting on it to happen again.

the middle digit on my digital multimeter is crapping out. the handheld read 1_.0. the fixed bus meter says 13.9.

everything seemed fine until i shifted into drive. then a load shows up on the battery. maybe in half an hour that will have drain the battery. im sitting here watching and waiting.

fwiw there is a belt squeal going on too
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Old 01-06-2019, 04:03 PM   #7
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where is the voltage regulator? i thought it was internal to the alternator.

when in drive, the load on the meter varies from about 5.0a to as large as 11.0a. thats sitting at idle. if i stomp on the fuel, the meter flips over to charging.

maybe the alternator is fine and i have a short from the trans? idk
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Old 01-06-2019, 04:52 PM   #8
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Quote:
Originally Posted by turf View Post
where is the voltage regulator? i thought it was internal to the alternator.

when in drive, the load on the meter varies from about 5.0a to as large as 11.0a. thats sitting at idle. if i stomp on the fuel, the meter flips over to charging.

maybe the alternator is fine and i have a short from the trans? idk



Most regs are internal to the alternator. Don't know about your engine.


Why are you putting it in drive to test? Neutral at low, high idle and at 2000rpm and hold it there.


Sounds like belt is loose, not tight, if squeaking. Wd40 on alternator pulley and into the front bearing area of it. Couple of squirts will help.


Warm your meter up before testing if you are working out in the cold, might help the display read right.


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Old 01-06-2019, 05:07 PM   #9
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The heater grids for starting can cause this. I have had the seleniod for the heater stick on and run the battery down overnight. problem was it only did it sometimes. Also when running if it cycles on and off it will pull down the voltage each time it comes on. It should only do it when the intake is cold. However it may well be intermittantly on when it should not.

On the Dodge trucks the alternator is externally regulated. A small simple regulator for 89 through ? by 96 it is in the vehicle computer.
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Old 01-06-2019, 05:36 PM   #10
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with the engine not running but key on, i detect no faults in the drive selector.

its cold, so maybe the heater grid is coming on. with the engine off, i had to wait for that to shut off to check the voltages so i think its working.

in Park, the Amp draw is 0 - +2A charging
in Drive, the amp draw goes from -5 to -11A discharging

it killed the battery while running. took it down to 11v when i shut off the bus. its recovered some and showing 12.3v now.

the heater grid would explain the variable 5-11a draw. what im missing is why im killing the battery in drive.
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