Alternator not charging for a bit at startup. - Ford Powerstroke Diesel Forum
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Old 11-07-2012, 04:28 PM
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Alternator not charging for a bit at startup.

I have an 00 Excursion. Recently noticed that the battery voltmeter on my Edge programmer was showing 11.7 volts when the truck is first started. After 30 seconds to a minute, the volts jump up to 14.3 and stay steady there.

Measuring at the batteries, I was getting about 12.5 volts (after the truck sat for a few days) before starting. When I started it, the volts measured about 12.0 for 30 sec to a minute. Then jumped up to 13.6-14.5.

I replaced the alternator tonight. No change in output.

Coincidentally, I noticed all of this about a day after I jump started my lawn tractor battery with the truck.

I just disconnected the battery cables. My plan is to check for a voltage drop in the batteries overnight. Also in the morning am going to load test each battery. I believe the (Motorcraft) batteries are about 2 years old.

Any ideas or directions.

Steve H.
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Old 11-07-2012, 04:36 PM
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Sorry to say this but you just wasted your time and money. What is happening is normal. When you turn the key to run the glow plugs come on for up to two minutes and draw a considerable amount of current. When they switch off the alternator catches up and the voltage goes up. The voltages you listed are 100% normal.
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Old 11-07-2012, 04:57 PM
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If this is normal I am just wondering why I just noticed it. I have had the truck for over a year, and know my cars/trucks well. I would consider anything under 12.6 a discharge.

If anything now I have a spare good alternator.

Steve
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Old 11-07-2012, 06:03 PM
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Batteries generally run 2v per cell optimal so 12.6v for the string is just the surface charge. A load test should bring it down to 12-12.2v. Now if your measuring the 12.6v while the truck is running, it would be a lack of charge current either because the alternator wasn't working or the load exceeded it's output. It's hard to say why you just noticed it, perhaps you were subconsciously looking for electrical issues after working on the lawn tractor or perhaps you have a loose connection or a bad GPR and it just started working again. Either way a normally functioning truck will draw 100+ a just from the glow plugs when you turn the key to run. A stock alternator outputs about 130a but not at idle. If you want to do a experiment, turn the key to run, wait up to two min for the glow plugs to shut off and see if the voltage is where you expect it. Alternatively you could temporary disconnect the GPR to see if the voltage is like the other vehicles you have worked on.
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Old 11-09-2012, 02:46 PM
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Thanks for the ideas about troubleshooting the system. Today I did load test the batteries, and they both dropped to the lowest point of the "GOOD" area. Then I noticed that the pass side battery was stained on top. I pulled the vent caps, and found one cell very low on acid. I filled the cell, then put the battery on the charger for the afternoon.

Will be checking into it more tomorrow.

steve
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