Alternator: 30 Amp Output? - Ford Powerstroke Diesel Forum
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post #1 of 7 Old 02-07-2012, 01:49 PM Thread Starter
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Alternator: 30 Amp Output?

Hopefully a quick question

Noticed in the past month or so that my batteries are slowly being drained, which makes it slower and slower to start. Once I put a charger on the batteries, they charge just fine and the truck starts quickly after that. Both batteries are relatively new Optimas and the truck gets driven every day or every other, but usually just around town.

So I thought I'd stop by Oreillys and have them test my alternator. Guy says it's showing the alternator is only putting out about 30 amps at idle. Seems awfully low to me... no?

However, I have yet to see any light on the dash about the battery/charging system and the little battery idiot-gauge in the dash shows "normal" for charging.

So my question is... how bad/low does the charging of the batteries have to get for the the warning light and/or gauge to show an issue?

Thanks in advance!

2001 F250 Superduty 4x4 Crew Cab Lariat Short Bed 7.3L Powerstroke

1990 F250 Custom RegCab 7.3L IDI
- New to me Feb 2012 (not running yet)
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post #2 of 7 Old 02-07-2012, 01:51 PM
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What voltage are you getting measuring at the batteries.
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post #3 of 7 Old 02-07-2012, 02:16 PM Thread Starter
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With the truck off, both batteries show about 13.4V. With the truck at idle they were both showing 13.8 or 13.9.

With the truck off though, I could watch the indicated volts on my meter slowly climb. Is that normal.... with it off? Maybe I need a new meter

2001 F250 Superduty 4x4 Crew Cab Lariat Short Bed 7.3L Powerstroke

1990 F250 Custom RegCab 7.3L IDI
- New to me Feb 2012 (not running yet)
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post #4 of 7 Old 02-07-2012, 02:36 PM
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Truck running should be higher. Min. 13.3 max 15.5. should be in the 14 to 14.5 volt range charging seams weak. Did they do a cold crank amp test of batteries. Mine has been weak on starts & worse when not plugged in. I have so many cars & trucks between work & home I bought a good tester that tests everything. One was 575 & 115 to 400, the longer it sat the lower the cca would be. 14.75v when truck is running. My money's on the alt. take it to a rebuild shop or buy a new one. Never had good luck with remans, what good is lifetime warrantee if you have to change it every year.

Last edited by letitsno; 02-07-2012 at 02:41 PM.
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post #5 of 7 Old 02-07-2012, 04:07 PM Thread Starter
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Thanks for the info letitsno... I'll order up a new alternator.

But just so I make sure I don't have an issue with my gauge cluster.... can anyone answer my original question? "how bad/low does the charging of the batteries have to get for the the warning light and/or gauge to show an issue?"
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post #6 of 7 Old 02-07-2012, 11:01 PM
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Don't pay any attention to the gauge cluster, it's just a fancy idiot light. Also remember your glow plugs stay on for up to two minutes after you start the truck so the voltage won't come up till they are off. The WTS light does not indicate the glow plugs are off.

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post #7 of 7 Old 02-08-2012, 03:58 AM Thread Starter
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10-4, thanks. I'll order a new alternator and some new battery cables this week and see how it goes.
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