What should battery voltage be?
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Elder User
Joined: May 2008
Posts: 550
Likes: 0
From: Sioux City, IA
What should battery voltage be?
I am getting the following using ScangaugeII:
Voltage w/ keyoff: 12.5
Voltage w/ key on after glow plug light turns off: 10.9-11.1
Voltage after about 30 sec of running: 13.9-14.0
I'm a little worried about 10.9-11.1. Seems low. Think my batteries are shot?
Voltage w/ keyoff: 12.5
Voltage w/ key on after glow plug light turns off: 10.9-11.1
Voltage after about 30 sec of running: 13.9-14.0
I'm a little worried about 10.9-11.1. Seems low. Think my batteries are shot?
Hotshot
Joined: Aug 2006
Posts: 17,398
Likes: 317
From: Whittier, CA
Sounds good.
Sounds a bit low. I've never seen mine drop into the 10's. Your reserve amps might be on the low side. How old are these batts? Not the originals, I hope. Right here is where your FICM is most vulnerable, with glow plugs on, voltage low, and you hit the starter. I would get those batts load tested.
Your alternator is working good.
Sounds a bit low. I've never seen mine drop into the 10's. Your reserve amps might be on the low side. How old are these batts? Not the originals, I hope. Right here is where your FICM is most vulnerable, with glow plugs on, voltage low, and you hit the starter. I would get those batts load tested.
Your alternator is working good.
FTE Legend
Joined: Jul 2005
Posts: 65,938
Likes: 1,432
From: Millersville, MD
Check fluid level in the battery (s). 12.5 is starting to get low too....Mine (fairly new) is running 12.7 -no load. Agreed - the alternator is doing it's job.
Maybe get it (them) load-tested.
Maybe get it (them) load-tested.
Freshman User
Joined: Dec 2008
Posts: 47
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From: Fort McMurray/Alberta
That sounds good to me, I believe just because the glowplug light is off, it doesn't mean the glowplugs are off, so you still have a 180 amp draw till they turn off.
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Fleet Mechanic
Joined: Jun 2006
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You disconnected the alternator output and ran it through a ampmeter to verify no alternator output?
If true, I'll have to get my electrical diagram out and see how Ford cuts off the alternator. I assume they interrupt the exciter field voltage.
DSMMH
Lead Driver
Joined: Sep 2007
Posts: 8,180
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From: Scio, OR
This is a question I had for a long time and I finally tested it with a clamp ammeter.
The voltage regulator in the alternator is turned on by the I circuit. In a single alternator setup, that circuit goes to the instrument cluster and is part of what controls the battery warning light.
The instrument cluster does not apply voltage to the I circuit, thus not turning on the alternator, until the glow plugs have shut off.
The test I did was to put the clamp ammeter on the B+ wire coming out of the alternator. I then started the truck cold and observed little voltage (less than 5 volts) for about 90 seconds. Then I observed it go up to about 90 amps.
The voltage regulator in the alternator is turned on by the I circuit. In a single alternator setup, that circuit goes to the instrument cluster and is part of what controls the battery warning light.
The instrument cluster does not apply voltage to the I circuit, thus not turning on the alternator, until the glow plugs have shut off.
The test I did was to put the clamp ammeter on the B+ wire coming out of the alternator. I then started the truck cold and observed little voltage (less than 5 volts) for about 90 seconds. Then I observed it go up to about 90 amps.
Fleet Mechanic
Joined: Jun 2006
Posts: 1,589
Likes: 20
This is a question I had for a long time and I finally tested it with a clamp ammeter.
The voltage regulator in the alternator is turned on by the I circuit. In a single alternator setup, that circuit goes to the instrument cluster and is part of what controls the battery warning light.
The instrument cluster does not apply voltage to the I circuit, thus not turning on the alternator, until the glow plugs have shut off.
The test I did was to put the clamp ammeter on the B+ wire coming out of the alternator. I then started the truck cold and observed little voltage (less than 5 volts) for about 90 seconds. Then I observed it go up to about 90 amps.
The voltage regulator in the alternator is turned on by the I circuit. In a single alternator setup, that circuit goes to the instrument cluster and is part of what controls the battery warning light.
The instrument cluster does not apply voltage to the I circuit, thus not turning on the alternator, until the glow plugs have shut off.
The test I did was to put the clamp ammeter on the B+ wire coming out of the alternator. I then started the truck cold and observed little voltage (less than 5 volts) for about 90 seconds. Then I observed it go up to about 90 amps.
DSMMH
Senior User
Joined: Feb 2004
Posts: 417
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From: Southdakota
Thanks for jumping in there guys!
I had to work today :0(
I noticed this when I replaced my alternator a couple days ago and had to dig in to it a little to figure out why also. Not sure I still know WHY Ford does it this was but i now know what i am seeing is correct.
Gould it be that the GP's draw more then the single alternator can handle so they just decided to keep the alternator off until they cycle off?
I had to work today :0(
I noticed this when I replaced my alternator a couple days ago and had to dig in to it a little to figure out why also. Not sure I still know WHY Ford does it this was but i now know what i am seeing is correct.
Gould it be that the GP's draw more then the single alternator can handle so they just decided to keep the alternator off until they cycle off?