What should my alternator be putting out?
 

I've having some problems with my battery draining over night. The battery is an AGM version from oreilly's and it was purchased last november. The battery tester at oreilly's is showing good battery and the alternator output was 48A on the first test. I tested it again at another oreilley's and it was 63A. The alternator does hum a little when it's under load, if that means anything. As long as the battery is showing 'good' on their tester, I feel like they're not going to help me. Can someone confirm if that's the proper range for an alternator in a 2005 f series?

i believe it should push about 110a that is what a stock one should run.and a tow package should have 130a. and if it drains overnight i would check your grounds? good luck

that is on the 5.4s dont know if its the same for 4.6.

I always thought that rating was for maximum output depending on load.

yes that is at about 6000 rpms!!! and at 2000 rpms it should be around 70a.

but that shouldnt drain your battery unless you are driving. that is why i said a ground possibly.

If its RPM related, its going to be something that changes speed as RPMs do. Therefore it is going to be something connected to the engine. Pulleys and accessory bearings fit the bill as they are driven by the crank pulley!!

A bad ground wouldn't cause it to die overnight, something else is draining it overnight whether it be something not turning off or a short somewhere.

The 2004 + MY F150s, the charging output is controlled by the PCM.

The set point voltage is sent from the PCM to the regulator, and a second circuit communicates the alternator load and error conditions back to the PCM.

The charge voltage is set by the PCM, higher voltage for a cold battery, lower voltage when the battery is warm ( PCM uses the IAT as the temp gauge ).

The PCM can also increase the idle speed if the battery is drained.

Not sure what the method was used by oreilley's to test the alternator or if the regulator was included in this test ( doubt it ).

Might want to start with asking them what they tested before calling the alternator bad and when they tested the battery, how long did they have it ?
A true load test, they need to charge the battery back to full capacity before doing a load test, else if they just slapped the tester on it, you could have done a better test at home overnight with a charger and meter.

they just used a handheld tester. It was made by Autometer, and looks something like this, though I don't know if this is the exact model.

http://test.autometer.com/productDet...tID=58&isKit=0

I think I might have found the source, but I'm not entirely sure. A few months ago, I bought a dual USB accessory charger that I installed in the cigarette lighter port. I know that port is always on whereas the 12v power point is switched, but I assumed that as long as I didn't have an accessory plugged into the port, there was no load, and therefore should be no drain.

After the trip to Oreilly's today, I pulled the USB plug and went into work. Usually, by the time I get out of work, you can tell the battery is getting weak and the engine is a little harder to turn over. It fired right up today. If it's not the USB plug, it should be near dead tomorrow morning, and I'll let you know.

The only other aftermarket electrical item I have is an electric fan with a FK25 controller from DC controls, but I know that is also wired to a switched 12v wire.

So it looks like it was the USB plug. Unbelievable. Truck has had no issues starting after sitting awhile since I removed it. I'm not sure, but the plug must have a tiny step down transformer to convert 12v to 5v. That must have been the drain.


Edited for language

^lol

Yea those things eventually wear out and never "switch" off, my mom had a battery that kept dieing in her old car and it ended up being from her worn out off brand cell phone charger.

I'm still having some trouble with drain or losing charge. It hasn't been low enough that it won't start, but when it turns over, you can tell it's having a hard time.

Something strange is going on with the gauges and/or door switch. Sometimes if I get out of the truck while it's running, the door open chime will go off again randomly. I've heard the door switch can cause problems with batteries, but since the lights shut off after the truck has been shut off for awhile, I don't know. Also, after my truck has been shut off and the gauges rest, they'll float a little before resting again. Any ideas?

I didn't see any problem with drain. I used a multimeter to measure current draw with the truck off and nothing even registered on the meter.

Hey SSCULLY, just wanted to give some more information if interested. The PCM determines battery temperature on IAT (as you mentioned), but also ect. We measure actual battery temperatures thru various wind tunnel/soak tests along with the above parameters. We model the parameters in an algorithm until they are within a reasonable range of the actual battery temp.

good to know. The Description and Operation from the 2006 service manual does not make mention of the ECT used with this.

they might do that, as not to make the operation description too verbose.

thanks again for a bit of insight I cannot get from the EVTM and service manual.