[FIXED] 2005 f250 charging

I am trying to help a friend out with his f250 6.0 diesel that has been having charging problems. The truck has many modifications (engine and electrical) and some of the electrical loads that I think are playing a role in the problem. It has 4 electric cooling fans that melted a 30 amp relay (story for another time and i didn't do the wiring), aftermarket high performance fuel pump, stereo system, HID head lights.

So the first problem came and the truck wasn't charging. Before i got to it they had put a known good alternator on it and it still wouldn't charge. I found there was a pin fitment problem on the wire that came from the charge indicator light that if memory serves excites the voltage regulator (its been a few weeks). Once a new connector was installed it was charging fine. Fast forward a month and it has two dead batteries. They jumped it off and it would sit there and idle and not die. While it was running for giggles I put my u scope amp clamp on it to see the output and it was about 65 to 70 amps, the voltage was only 12.5. Put in two known good batteries on it since they are the heart of the electrical system and at an idle the output amperage was about 65 amps. Output voltage was low like 12.7. After idling a while and what seemed like long enough to charge the batteries I looked at the voltage again 12.7 and still 65 amps. So I unplug the fans and the voltage jumped to 13.3. When revved to 1800 with all loads the voltage goes to 13.5 ish. So at this time I am thinking that there are too many loads for the stock alternator. Just to be sure I checked for parasitic draws and after 30 minutes the draw was 96 milliamps. At this point I am thinking that he has too many loads or am i missing something?

It depending a bit on temperature (cold weather low voltage hot weather higher voltage) a fully charge battery will show between 12.6 and 12.8 volts. but to actually put even low rate charge into a battery a minnimum of 13.1 volts is required.

A diesel shouldn't need extra cooling fans even if idling for prolonged periods in a hot climate, normally the problem with diesels is them running cool at low speeds. Because they don't have a throttle to restrict he air into the cylinders diesels engines are much more efficient at low loads and rpm than gasoline engines so less heat goes into the coolant.

Contiunual deep discharging of the batteries eventually causes them to lose charge storage capcity (Amp Hours), every time a battery is discharged below 50% noticiable damage is done to a battery.

The electric fans are in place of the engine driven fan, so they are the only method of cooling for the truck. Don't know the reasoning behind it but the guy is absolutely against putting the factory fan back in. So with the new batteries the charge voltage was still 12.7 at idle. Cant get it past there without removing some loads, like the fans momentarily. Am I right in thinking he is going to need a higher output alternator?

A combination of the alternator being too small and the the way the truck is being used. One low cost fix might be to fit a smaller alternator pulley but even then the voltage gain at low RPM will be small. I know from home built car forums that most cheap aftermarket cooling fans chew through a lot of current without moving much air, the more expensive ones are much more efficient.

Experience of dealing with customers over the years has taught me any attempt to get them to change they way the use a vehicle won't go down well, so it looks like a bigger alternator is the only option. Eric at SMA had a similar issue on GM 2500 HD recently a replacement alternator he fitted wasn't charging at anything linked the rated specification.

A higher output alternator fixed the issue