Hi all,
I acquired a 2002 F150. It had the electric fan modification (not working) and still had the mechanical fan too. I ran it like that for 2 years or so and never had any trouble until the mechanical fan stared hitting the electric fan mounting bolts. Long short is I decided to fix the electric fan rather than try to hunt down a mechanical fan shroud.

Fast forward some months and I started seeing my battery gauge on the dash wobbling and then had some serious issues driving. Limped it to the parts store, got a new battery, and that fixed it right up.
Fast forward some more months and tonight I saw the gauge wobbling again when I was idling at a fast food restaurant for a long time (10 minutes at least).

I'm wondering if my alternator wasn't producing enough amps at idle to run the fans causing the battery to discharge. Once I got going, the voltage stabilized. I repeated the test when I got home. AC on (e-fans on), and voltage wobbled. AC off (e-fans off [I think they were off]) and no voltage wobble.

I can't find any decent resource to tell me how much current I should expect from my alternator except from this random manufacturer that suggests there is an exponential decay of amperage below 1000 rpm. https://balmar.net/balmar-technology...output-curves/ Could be as low as 20 amps or less, which is less than my fans draw (I think).

So... does anybody have any experience with these electric fans causing issues at long idle? Should I look into getting a high-output alternator or is this more likely that my alternator is just going bad?

Thanks,
Matt

 

There's all types of videos available on how to test your alternator. Or, take it in for testing.

As far as your fan, maybe use a clamp meter to see what amperage it is drawing.

 

Have the alternator correctly tested.

 

Roger that. I’ll see what kind of testing I can do myself. I read some tales of auto parts failing or passing alternators based marketing instead of amperage/voltage.

In the mean time, does anybody know how much current I should EXPECT at idle? I also noticed my idle rpm doesn’t increase when my AC is on, which based on a different forum I stumbled across, it should.

I also have a couple hundred more rpm if I have it in park rather than in drive, but stopped with foot in brake. Is that normal too?

 

Normal to have higher idle in park. Is one fan running or both at same time ? Both fans may be too much for alt. at idle. The AC on should raise idle thru IAC valve, but no idea how to make it happen. I got a mechanical fan on mine and am very happy with it (happier now). Good luck

 

Both fans run at the same time. I am suspecting the fans are drawing too much current, but would love some confirmation. I guess I need to go buy a clamp on current meter, stick it on the battery. Current into the battery says it’s fine. Current out of the battery says the alt is underrated or going bad.

 

A properly functioning of alternator would not let the battery discharge in normal driving.

Maybe.... Maybe it doesn't put out enough at idle.... But how much time do you spend at idle?

They working alternator should easily put out the amps needed under normal driving. And the battery can easily provide it for short periods of time idling if they alternator doesn't

I absolutely love my clamp on DC amps reading multimeter. Well worth the money . Sooooo easy . Heck it paid for itself the first time I used it to figure out why a compressor on RV AC wouldn't start ... Turned out to be a bad connection. The inrush amps were too low and the capacitors were good.... So something else was limiting the current.

So easy to find parasitic drains too..... And low output from alternators when batteries aren't fully charged....