A couple of weeks ago my battery light came on briefly while driving to the airport at 4am. It went off after about 10 miles and didn't come back on the rest of the drive (I live 80 miles from the airport in Roanoke). It sat in the airport parking lot for 9 days before I got back. Started right up but since then the light has been coming on periodically.
I have been keeping my scanner hooked up while driving it the last few days. Voltage at the ECU is always in the 13.7-13.9 range unless the light comes on then it starts dropping. Went as low as 11.4 this morning. When it did the headlights shut off. I had them in auto at the time and immediately switched them on manually as I was going down the road at the time. Once I had switched the lights on the battery light went back off and the voltage came back up to 13.8 immediately.
I am thinking the excitation voltage for the alternator is dropping out periodically. Where is this signal generated in the system?
Anyone have an idea?
Also the batteries are 18 month old interstates and I have never had an issue starting this truck even in 0 degree weather since they were installed.

Thanks for any input you may have.

 

Need some more information to help.
What year?
How many miles?
Have you ever replaced the Alternator?

 

Ok lets try this again (3rd time)

06 F250 131k miles. Original alternator.

 

Symptoms sound like a failing alternator. How old are the batteries and have you had them tested?

 

If it is your alternator you might want to take a look at DC Power. bismic replaced his with a 190A. I trust his judgement on what to use.

www.dcpowerinc.com

Might want to have your batteries load tested to see if they are functioning correctly even though they are only 18 months old.

 

Was thinking alternator. Didn't want to go there right now but what else can you do. Is there a source for new internal regulator and brush kits like on the older trucks. My 93' is still running the original alternator at 260k I've just replaced the brushes or regulator depending on what fails. I will load test the batteries as a precaution. Might as well take advantage of the warranty if need be.

 

So does anyone know where the voltage to signal the alternator to start charging is sent from? ECU perhaps? If so what is the source of input to determine it's time to start charging?

Also an update. Today while going down the road battery light came on. Scanner said 13.7 volts at ecu the whole time. Later on a different short trip it came on almost immediately after starting. ECU voltage read 12.1 and slowly climbed to 13.0 as I drove to the main road. When I pulled out into traffic voltage went down to 11.6 and stayed there. After about 10 minutes the light went off and voltage immediately jumped to 13.5. It stayed there and within about 2 minutes the light came back on but the voltage never dropped and the light went off again in another couple of minutes.

I really wish it were possible to just replace the regulator inside the alternator as it doesn't seem to be having any problems charging when it chooses to it's just sporadic.

Anyhow I'll stop rambling now.

 

I had simillar problems with my 06 6.0 cc fx4 king ranch single alt system. pulled the alt and took it to a repair shop. $75 bucks got me a new "diode plate". batteries load tested good. everything went well for a couple of weeks and then, intermitten battery light again. pulled the alt and took it back to the shop where they said it failed after 10-15 min running on the bench. another diode plate (no charge) and this time my passenger side battery failed load test. New batteries no problems for a few weeks now.
The guys at the alternator shop told me this is a common problem and that the diode plate is the rectifier AND the voltage regulator. the work on all our city vehicles and have defaulted to a philosophy of keep changing it 'till it stays fixed. Sounds kinda like a scam I know, but they repaired my the second time for free.

BTW- Nice looking truck Dirtleg!

 

Wow! thats cool, 170amps at 1800 RPM. I wonder how many amps (or KW) of AC power you could make using a solidstate inverter. Anybody know how to do the math on that?

 

The voltage regulator and brush assembly are an integral unit and must be replaced together--no separate brushes available. The diodes are part of the rectifier assembly. The voltage is controlled by the hybrid gauge cluster not the PCM unless you have a dual alternator setup in which case only the second alternator is controlled by the PCM.

To the OP: You're better off going with a high quality replacement alternator like the DC vs. a rebuilt/reman/lifetime replacement unless you're pretty handy with tools and don't mine changing it often.

 

Basically Watts = Volts * Amps * an efficiency fraction

170 Amps at 13.8V equals apprx 2350 Watts, but you have to derate it due to all the "system losses".

Here is a good site on inverters:

http://www.donrowe.com/inverters/inverter_faq.html

 

Partsman I agree with your philosophy on replacement parts. Plus it is really just a scam on the lifetime part. All they end up doing is changing their part number and voila no more lifetime replacement as that part is no longer available. AZ and Advance both do it for sure. Happened to me.

Really the issue is I just like fixing what I've got if possible rather than replace it.

Thanks for the replies and it appears as I'll be going the DC power route when the time comes.

And it saddens me that ford depends so much on the unreliable instrument cluster.

 

Realistically your issue is probably in the brush/regulator assembly. It's not that hard to change but you have to be careful with the plastic (don't remember the exact term) piece that centers the rear bearing when you disassemble and reassemble as it breaks really easily. There is a plastic lip around it that can be trimmed with a knife to prevent it from breaking with just a little "shave". An alternator shop can repair them fairly cheaply with brushes being about $40 plus labor. Not one of motorcraft's better parts.

 

Thanks for that info. Any chance you know the part number for the brush/regulator assembly. I am willing to give it a go if I can get the parts.

 

I do not know the part number, I just know there are two different ones.

Check the F600 and F601 on this page: National Quick Start Sales, High output alternator, Alternator & Starter Parts - FORD

It should be the F600 type. The F601 is for PCM controlled alternators which the Superduty's only have on the second alternator of a dual alternator setup.