Alternator voltage output
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Alternator voltage output
The batteries in my car hauler haven't been charging. So i traced it back to a blown 30 amp fuse. Replaced that. When i fired the truck up (2008 6.4 F-450) i notice that the voltage at the truck batteries was 13.15. And the voltage at the trailer batteries was 12.88. I always thought the alternator was suppose to charge 12 volt batteries at 14.2. Granted the truck was at idle. Does the voltage increase with rpm. I just found this a little odd.
Whats your take.
Thank you in advance,
Steve Tucholsky
Cleveland, Ohio
Whats your take.
Thank you in advance,
Steve Tucholsky
Cleveland, Ohio
Token Redneck
Joined: Jun 2007
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From: Breckenridge, TX
A SD killing an alternator wouldn't be a first. The 6.0 came with a 110A alternator that can't even run the glow plugs, my larger 140A unit just died at 95k miles.. I know the 6.7 has an optional 200A unit, so I'd guess the 6.4L alt is somewhere in that range most likely 110A to 140A, but IMO the alts that come stock are small and just waiting to burn out. Each battery puts a 7-10A load on the alternator, so multiple batteries on the trailer plus two in the truck and body electric might have been too much for the original unit to handle.
Mine started like yours, voltage at the batteries started falling slowly and once it hit 13.0-13.2V at idle regularly it's like the alt just flat died and started bottoming out to 12V at idle once the truck got hot.
Upgraded 6.4l alts:
http://www.ficmrepair.com/index.cfm/...=cat/cat84.htm
Call the number on that website, ask for Ed and he'll spend time with you on the phone to answer your questions about alternators. I just ordered from him last week after spending 20 minutes on the phone with him.
Mine started like yours, voltage at the batteries started falling slowly and once it hit 13.0-13.2V at idle regularly it's like the alt just flat died and started bottoming out to 12V at idle once the truck got hot.
Upgraded 6.4l alts:
http://www.ficmrepair.com/index.cfm/...=cat/cat84.htm
Call the number on that website, ask for Ed and he'll spend time with you on the phone to answer your questions about alternators. I just ordered from him last week after spending 20 minutes on the phone with him.
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From: Stephensville WI
Measure your voltage at the alternator at idle and at around 200 RPM.
Measuring at the trailer battery alone isn't a very good measurement by itself, you're seeing a voltage drop across the wiring harness and through the trailer connection, but unless you know what the starting voltage is the drop is "unknown".
Measuring at the trailer battery alone isn't a very good measurement by itself, you're seeing a voltage drop across the wiring harness and through the trailer connection, but unless you know what the starting voltage is the drop is "unknown".
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Measure your voltage at the alternator at idle and at around 200 RPM.
Does the voltage increase with rpm
The trailer batteries at 12.88 is low, but at idle with loads and a lot of distance (wire resistance) at idle that could be normal. The key is that the battery voltage at the trailer should be above 13V at increased idle with or without other loads on the alternator.
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Oh okay (David) now that makes a little more sense. I just figured that the voltage should still be at 14.2 at idle. What if your in traffic idling for a long time. You still need the batteries recharging. But then again if they are topped off, they might not need as much.
(Red-ford). Yes, thats what i was thinking at first. There is a drop all the way back to the trailer. I kind of expected a little. Im assuming its like a trickle charger with such a small wire running to it. And most likely your going to be driving hours so it gets a good chance to recharge. But it was after seeing the lower voltage at the trailer that made me look under the hood. And see that it was only at 13.10.
But the truck is at Valley ford as we speak. So we'll find out if im just over reacting or not. I hope its normal operation. I do long trips on the weekends racing. Just dont want to be coming home Sunday night and have it fail. Ill keep you all posted.
Thank you again for all your reply's
Steve Tucholsky
(Red-ford). Yes, thats what i was thinking at first. There is a drop all the way back to the trailer. I kind of expected a little. Im assuming its like a trickle charger with such a small wire running to it. And most likely your going to be driving hours so it gets a good chance to recharge. But it was after seeing the lower voltage at the trailer that made me look under the hood. And see that it was only at 13.10.
But the truck is at Valley ford as we speak. So we'll find out if im just over reacting or not. I hope its normal operation. I do long trips on the weekends racing. Just dont want to be coming home Sunday night and have it fail. Ill keep you all posted.
Thank you again for all your reply's
Steve Tucholsky
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Okay. Here it is. Just got the call from Valley Ford. DavidB was right. The alternator is controlled completely by the PCM. The more demand put on the system. The more voltage output from the alternator I just figured the voltage would stay constant. But then again the voltage and current output are proportional. Cant have more of one, and not the other.
Thanks again for the comments. It was worth looking into.
Steve
Thanks again for the comments. It was worth looking into.
Steve
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