Hey everybody, hope all is well!

I just went out and started my truck to let it warm up before i headed off to the city and noticed my lights were dim and there was a new noise under the hood, it sounded like the secondary fuel pump starving for fuel, so i shut it off, cycled the key and made sure the fuel wasnt gelled and the pump wasnt starving for fuel, which it wasnt. i live in new york and we've had temperatures in the negatives for a solid month now so checking my fuel is an everyday thing right now. Anyway, i pulled up the battery volt meter gauge on my H&S and sure enough it was only reading 11 volts. So, i have the dual alternator set up on my truck and i thought if one went down, the other one would carry the load of the truck but apparently not?? is there a fuse or anything i can check just in case? i believe the driver side alternator is toast, as i smelled a burning smell as the truck was running and checked under my hood and sure enough, smoke was rolling out of the alternator. I unplugged that alternator to see if the other one would start charging the system but it didnt. and when i came back inside to look through my book for a charging fuse, the truck was totally dead in five minutes time or so i went back out to check things. i also took the batterys out of my cummins and swapped them to make sure i didnt have a bad battery too. Sooo, just a few questions, is the 6.7s charging system not set up so one alternator can take over? Is there a charging fuse i can check? Is there any way i can check to make sure atleast one alternator is actually good? Or should i assume both alternators are bad?? This has me puzzled for sure.

 

Baed upon what you have said, Replace the one alternator and if you want you can test the other, but unless you have forscan or IDS you would have to bench test that alternator for current output.

the other piece of the puzzle, why no charging or pickup up the load is good question. I think the issue is you opened the circuit when you unplugged the bad alternator.

 

Well i hooked my matco maximus up to the truck today, it was dead last night, and read generator 1 and 2 data, generator 1s load percentage was sitting steady at 65%, commanded voltage was at 14.78 volts but actual was only 11.8 volts. it had a readout for a hertz, which read something like 162,000 which i have no idea what that means but it seemed high to me. Generator 2s data showed its load percenage being pulsed at 58%, its hertz reading was much lower. So i think on dual alternator systems on our 6.7s they act as one big one rather then two seperate ones and if one goes down, the other one is not strong enough to keep up. Actually the other alternator probably is more then capable of keeping up, it just looks like the PCMs programming wont allow it to. As even with the computer detecting a fault in one alternator, its still not telling the other alternator to operate at 100 percent capacity. Rather 58%. Also i put my volt meter right on both alternator live power wires and they both read 11.8 volts. And the driver side alternator is squealing, and has a smell coming from it. Id say that smell is whats left of the rectifier.

 

2020 dual alternator

 

Thank you very much for the wiring diagram, i believe that diagram is for a 2020 powerstroke though as it says it is at the bottom of the diagram and i checked and unfortunately the fuse box numbers dont match mine. looks like the newer trucks go up to atleast 203 where as mine stops at 108 lol. Id really like to check the fusible links and fuses for corrosion or an open short as i pulled both batteries last night and charged them up so i could pull it in my garage this afternoon. I put the batteries back in the truck this morning, started it up and shut it off, let it sit and now 6 hours later, both batteries are completely dead. So then i pulled my cummins up to to jump it, hooked it up, went back inside and fed the fire to let the truck charge for ten minutes or so. came out and my 6 gauge jumper cables that have been with me through hell and back and have never had an issue, have gotten so hot they melted a hole right through the coatings. I've never seen anything like this. Is it really possible for a bad alternator to dump that much juice? its more probable there is an open wire playing welder somewhere or just straight dropping the juice right??? im afraid im gonna bolt this new alternator on and the draw is going to smoke this new alternator so i'm trying to be thorough. ive had 7.3s all my life and have had dead batteries and alternator issues and have never had this type of issue. ive always atleast been able to charge the truck enough to drive it inside to change the alternator...

 

I was just reading my past posts and i totally forgot to even say what the truck was, my truck is a weight reducted 2011 ford f350 6.7 lariat obviouisly with the dual alt setup. I sincerely apologise for the lack of info i provided earlier, ive had my head up my butt trying to figure this thing out and this is the first actual problem ive had with the truck aside from wheel bearings and brakes. So it also caught me way off guard. Thanks for the replies and the info so far though, i really do appreciate it!

 

Yeah the diagram is for a 2020. I don’t have anything for older trucks.

 

Well i appreciate the diagram anyway, and i definitely checked to see if there was some type of resemblance between the two but they must of revamped the wiring. i can clearly see a white scorch mark inside the alternator where something has gotten hot and there is resistance as you rotate the alternator pulley, so i'll know tomorrow night or tuesday night whether it was just the alternator or not. Its kind of unfortunate though. all this time ive had this truck and i always had a sense of security travelling and having two alternators, thinking i could lose and alternator and make it home on one. luckily this happened in my driveway for once. Thanks again everybody, i appreciate it.

 

Disconnected, I had 10v on my pax battery while my drivers batter showed 12.5v

replaced both batteries and volts are in sync.

2019 6.7 with 10k miles at the time.

there was corrosion on pax side battery terminals

 

From what I've read, the typical execution is that one alternator is on while the other is off to cool down. They are controlled by the truck - they do not function independently. It's like a drone that has some smarts but not enough to function autonomously.

 

Just curious. Would that have been covered under warranty? Seems low miles for batteries to be replaced.

 

In smart mode, they are controlled by the pcm

initially 1 alternator delivers smart voltage of 14.5

when the main alternator approaches a predetermined %, the secon alternator produces smart voltage of 14.5

typocally, both alternators are not the same size and interesting the smaller one is usually the initial one.

 

Well honestly, i used to work at ford and those batteries would of been covered under the 12m/12,000 warranty. no questions asked new batteries installed for free. Thats the way it should of been addressed anyway. Both my batteries are downstairs being maintained by my snap on charger and theyre both load testing good. And thats correct, the alternator that cooked was the 200amp alternator, which nobody had in stock so it'll be in tomorrow. My other alternator on the passenger side is a 157 amp alternator. When i checked the readings the computer was commanding the 200amp alternator at 65 percent and was commanding the 157 amp alternator to 58 percent. and even though the check engine light was on and you could read that the generator 1 as they call it, had a low voltage fault, it was still being commanded. The computers programming did not up the command percentage to the 2nd alternator at all. but i think the open short was sucking the juice faster then the 2nd alternator could keep up with anyway. Im going to check the readings on the alternators tomororow night after i get it up and going again and watch its commands. Long ways from a one wire alternator on a 350 modified hehehe

 

Speakerfritz, when you say smart charging, what do you mean? When i was watching the percentages on the alternators, the 2nd ones reading was flashing, like it was being pulsed. Initially i thought it was my scan tool having an issue with the reading but maybe thats an example of that smart charging mode?

 

Great thread guys I have a 2023 Renegade with a lithium upgrade. My F 550 has two alternators and two batteries. The batteries are in parallel. Looking at the wiring diagram it appears each alternator goes to separate batteries. But why if they are in Parallel.

It appears as if 12 volt power comes from one or both of the batteries to a BIM battery isolator then feeds around 70 amps to the lithium batteries.

Am I to assume that each alternator will always see a battery in line? The reason I ask is you never want to disconnect a battery from a running alternator.

Thanks in advance - Mike