pulsing ammeter

dale kahler

New User
I recently replaced the generator for an alternator. Its a delco internally regulated 2-wire setup using a 2 1/2" pulley to keep the rpm in a proper range. The battery is charging at 14.6 volts, the ammeter is discharging when lights are turned on, engine on or off-normal. I have eliminated the internal regulator as usual and made sure the ground is solid. The ammeter pulses at any rpm above 800, as well as the lights slightly as expected. I know plenty of people who are familiar with this problem but no solution yet. I even tried running a temporary ground directly form the battery to the alternator to make sure the ground was solid, no difference. The alternator is a 37 amp and the ammeter is a 60 amp on a D17 allis chalmers. Any light you could shed on this would be greatly appreciated. Many thanks!!
 
I'm confused: "The battery is charging at 14.6 volts, the ammeter is discharging when lights are turned on, engine on or off-normal."

If ammeter is discharging when lights are on and engine is on, then alternator has an issue.

The first thing I would do is remove alternator and take it to Napa or Auto Zone and have it checked out.

Second, I would also take battery to town and have it checked out too.

Third is where the fun begins. Someplace you have either a bad connection, or the lights are drawing too many amps, short. I once had ground strap with a lose connection.

My alternators don't start charging until the RPM's are above 1200. When alternator wakes up I can slow engine down a little and it still works.

I would also put a voltmeter on battery. Ammeter pulses, the voltmeter should pulse a little.

Good luck. Let us know what you find.
George
 
A slipping belt can also cause rhythmic pulsations in alternator output. Before getting in too deep with other stuff make sure the belt is tight, clean and seats properly the in the alternator sheave groove.
 
Good point Robert, how may times have you seen slick looking glazed cupped/dished out Alternator belts and dished out pulleys !!! Often times an alternator belt needs to be tighter then Dicks Hat Band to work properly, and that seems such an awful load on the bearings to me. Its amazing how much better the new multi grooved serpentine belts work and not as tight either. My truck AC compressor was locking up and the belt worked so good it could actually killed the engine, you wouldn't see that happen with a v belt, it would just slip and burn up. Also on my old 460 powered Ford RV's there were like 4 freaking belts to worry with and keep tight and adjust grrrrrrrrrr PS and AC and Fan and Smog Pump (or something like that, I forget) each had their own belts and the one that broke was ALWAYS the one in the rear so you had to loosen or remove alllllllllll the others to get to it grrrrrrrr Now my 454 Chevy has but ONE serpentine belt yayyyyyyyyyyy

Merry Christmas Bob

John T
 
Well one thing is 2 wire?? If you only how 2 wires hooked up instead of the correct 3 then that could cause some of your problem. But like Bob said a fan belt slipping will cause that also
 
What difference does it make if he has a one, two, or three wire system? I'm running some two and one wires and have not had any pulsing problems.
 
Very simple if the #2 wire is not there it will not sense the state of the battery and can in turn, turn on and off the alternator which would cause just such a problem
 
ASSUMING the belt is not slipping,do you have it wired correctly with the #2 "Voltage Sense" terminal connected to the large output stud, or, even better, to a point nearer the battery, such as the starter solenoid's battery cable terminal and the #1 "excite" terminal connected to an idiot light or fed from "ignition power" through a resistor or diode?
 
The belt is new and the pulley is the correct pitch and width and is also new. I actually bought a new 2 1/2" pulley with a 5/8" bore, then did some lathe work boring it to the required .670" bore and machining off the extra step. The belt is tightened enough so the belt can be depressed the same ammount as its width, this isn't my first rodeo. Yes the voltage sense terminal is connected to the output stud. The excite wire is run through a diode also. The alternator plug-in is new, the alternator has been rebuilt, but that doesn't mean everything is working properly. Obviously I am missing something and have considered alternator internal issues even though I rebuilt it. I have had the battery tested, it also is new. Ignition switch has also been replaced as it was long over due, this problem existed before the switch was replaced also. Thanks to everyone and their comments, we'll see what happens and I'll let you know what I find out.
 
Sounds like time to pull the alternator off and take it to an auto parts tore and have it checked on there test machine. All it takes is one small thing getting ad to make one not work as well as it should
 
I suspect your pulley is slipping on the alternator shaft. The pulley on the generator may be a little larger in diameter but the bore is the same and should fit right on your alternator. I've switched many pulleys from the generators to alternators so you can use the same belt.
 
dale, stick a small metal probe/screwdriver/awl/whatever into the alt "D" hole to bypass the VR & force full output & observe ammeter under those conditions.
 
probably wired alternator to wrong place and the amp meter is on the wrong side. Or charge wire is too small or mostly burned up...somehow high resistance or even open.
 
A swap from P ground to N ground will make an ammeter read backwards.
Does the pulsing occur at all rpms and all alternator loads ?
 
ok set your volt meter to AC VOLTAGE and see what it reads at the stud ,if you got a good meter you can tell it to hold that reading if any voltage over about 1 volt you will need new diodes in the alt
 
What does the voltage do with the lights on? If it drops below 13.2 then do as JMOR stated and full field the alternator, but only do so at fast idle and for no more than 10 seconds. Let us know what the readings are. All this assumes proper wiring. Gerard
 
In clarification about the ammeter discharging when the lights were on and the tractor running that was stated wrong. In reply to the pulsing issue I knew that the belt, pulley, wiring etc. were not the issue and liked to think a rebuilt alternator could be ruled out, but knew it couldn"t, but it was all that was left. I did take the alternator in and have it tested, to my delight it also pulsed the ammeter on the bench test. As it happens all too often new parts are faulty and this was the end result here on the rebuild. All the alternators I have built through the years and never an issue, there"s always a first! I bought a new 10SI delco alternator 2-wire, 3-wire whatever people want to call it, and this ended the pulsing as expected. Thanks again to all who commented in the forum and happy problem solving! Merry Christmas!
 
I know one thing, I can't measure a thing with a digital meter, takes an analog meter to measure mine when it is running. Digital won't settle, it just keeps wandering. ohfred
 

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