Help Alternator Issue
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New User
Joined: Sep 2009
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Help Alternator Issue
After replacing alternator and battery, the alternator still will not put out enough volts to charge battery. It's only reading 1 amp output no matter what. Any one have any ideas what else it could be
Post Fiend
Joined: Mar 2007
Posts: 26,966
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From: Texas
Welcome to FTE. Sometimes new parts doesn't mean they work, especially in the case of a rebuild. Are you measureing the voltage output with a meter to get the 1 amp? How about volts? Usually we check alternator output while running in terms of volts.
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I ment it's only putting out one volt no matter what. I took it to a part store that can check the alternator when it's on the vehicle. Plus it's the third alternator since the problem started. So I know it's not the alternator.
Post Fiend
Joined: May 2006
Posts: 10,007
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From: Central Florida
There are a couple of wires going into the pigtail. I think on 2 wire systems, they both should have battery voltage (12+). On a three wire, it needs the same as the 2 wire plus a ground. Then there are usually a couple of fuseable links on the charge wire (the big gauge). Confirm you have battery voltage at the wires on the plug with the key on, then with the engine running check the voltage on the alternator stud using the case as the ground.
1v output sounds to me like the field isn't being energized. I went through that problem when they sent me an alt with the wrong regulator installed. They don't cross over well, so double check it's right for your application.
How did you see only one volt when the battery should have brought the wire up to 12v or so?
1v output sounds to me like the field isn't being energized. I went through that problem when they sent me an alt with the wrong regulator installed. They don't cross over well, so double check it's right for your application.
How did you see only one volt when the battery should have brought the wire up to 12v or so?
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They tester at the part store hooks up to the battery and it can tell what the alternator is putting out also I tested all three alternators with a volt meter with out the power cable connected to the alternator and it always shows 1 volt. I also have replaced the plug that plugs intot he alternator. This problem started with the factory alternator so I know that I wasn't given a wrong style for the truck. I'm trying to figure out what else can cause the alternator not to increase the output when it needs to. Even when you disconnect the battery while running the truck shuts off do to no power. It should run off the alternator. So for some reason something is not telling it to increase it's output. I'm trying to figure it out before I take it to the dealership
Post Fiend
Joined: May 2006
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From: Central Florida
I'm not 100% on alternators, but the simple guest is. A stator is spun inside an energized coil. The magnetic field created by the coil, then drug across to a second coil by the stator, creates ~30v AC. The AC is then rectified into DC voltage and regulated down to ~13v. If you don't have an energized field, it's not capable of creating the high voltage AC to be rectified into you're charge current.
I suppose it could be throttled by varying the voltage into the field, but it seems wasteful to create and collapse the field on demand. Not to mention the voltage spikes it would create. Now with the dual alt diesels there was some bit of circuitry that activated the second the alt, perhaps your truck has something similar.
I suppose it could be throttled by varying the voltage into the field, but it seems wasteful to create and collapse the field on demand. Not to mention the voltage spikes it would create. Now with the dual alt diesels there was some bit of circuitry that activated the second the alt, perhaps your truck has something similar.
Posting Guru
Joined: Mar 2005
Posts: 2,060
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From: Burnsville, MN
The coil in the alternator has to be engergized. Perhaps something is interfering with providing current to the coil.... Maybe there's a separate fuse that blew when the original problem ocurred?
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Elder User
Joined: Nov 2008
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From: Northfield, MI
Why? What was wrong with it?
Why do you keep throwing alternators at it without diagnosing the problem?
Circuit faults.
That's a good way to fry modules due to voltage spikes.
No, it shouldn't.
Then as ReAX stated, you need to start with the basics as he alluded to. With the key on, use an incandescent test light to check the regulator circuits at the connector. There should be two terminals on most Super Duties and both should have power with the key on. If they both don't have power, then you need to trace the circuits and find out why.
This test is step one at this point. Check it then come back and tell us what you find. If one of the wires doesn't have power, note the color code of the wire and let us know.
This problem started with the factory alternator so I know that I wasn't given a wrong style for the truck.
I'm trying to figure out what else can cause the alternator not to increase the output when it needs to.
Even when you disconnect the battery while running the truck shuts off do to no power.
It should run off the alternator.
So for some reason something is not telling it to increase it's output. I'm trying to figure it out before I take it to the dealership.
This test is step one at this point. Check it then come back and tell us what you find. If one of the wires doesn't have power, note the color code of the wire and let us know.
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