Alternator output

Charging, starting, lighting, gauges, HVAC

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RandyP63
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Alternator output

Postby RandyP63 » Sun Jul 09, 2017 5:12 pm

I installed a new battery on my F-100, the truck would not start after a couple of trips, when I tried the volt meter on the new DieHard battery, it read 12.6 volts. I looked at the alternator and the previous owner put a Transpo 7078 one wire setup on it. There was a lot of heat damage to the BAT terminal on the Alternator. I had the alternator rebuilt, and returned the system to stock with a new voltage regulator from NPD.

On initial startup I had 14.2 volts, yesterday I drove the truck for about 100 miles, today though the output voltage from the alternator reads 12.9 , and when I turned the lights on it dropped to 12.6.

I have done a parasitic load test and it was normal, no draw. Any ideas? The truck runs great, but the battery dies after 3-4 starts. My next test is to load test the battery. Thanks.

Busboy
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Re: Alternator output

Postby Busboy » Sun Jul 09, 2017 5:58 pm

The latest episode of " I tried to reinvent the wheel". Leave your trucks stock people! :cuss:
1969 F-250 Camper Special, custom cab.
1967 F-100 4x4 custom cab.
2016 F-150 Eco-Boost 3.7 liter. (It will smoke the tires!)

RandyP63
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Re: Alternator output

Postby RandyP63 » Sun Jul 09, 2017 8:31 pm

Uh, I returned it to stock, but thanks for the insight, that is something I will use.

MadMike
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Re: Alternator output

Postby MadMike » Sun Jul 16, 2017 5:39 pm

FWIW, having a similar issue with neighbors '70 F250.

Ditched all the homemade 'house' wiring and extra battery/diode from P.O. Wiring is back to stock-ish. Has a 460 swapped in(from P.O.) place of the original 360.
Truck is an F250 w/ammeter which makes the F-350 diagrams more accurate for this truck.
'I' terminal is not used, it would be if there was a dash 'ALT' light.
Connector to Volt regulator is greem. IIRC this indicates the ALT is a 63 Amp unit.

Battery is at 12.6 Volts resting, less than a year old. Can spin the 460 no problem. Even when it has been drained it can still crank. Running, voltage is only 12.8, doesn't matter if there is a load or no load.

'I' terminal not used.
'A' terminal is constant Batt voltage. Yellow wire. Has a factory shared splice that goes to a capacitor mounted on the bolt for the regulator mount, firewall side.
'S' terminal is switched Hot. Turn ignition switch to 'ON' 11 Volts, jiggle key it can jump up to 11.8Volts, worn ign switch contacts. Green w/red wire. Has been spliced into for electric choke for Holley(Why they just didn't ring terminal it to the ALT *shrug*). I believe this should be with-in .5V of battery voltage.
'F' terminal goes to ALT. Orange.
A ground wire from the engine harness is attached to the opposite volt reg mounting bolt.

I haven't pulled the alternator but the wiring on the back looks pretty thrashed, it's intact, but ugly. Not sure if there was a proper Alt to ground cable installed.

Only Negative battery connection is main terminal to engine block. Pretty sure a ground to the body and to the Alt ground terminal is probably needed.

I would check to see what your switched hot is doing, and if the voltage is low, jiggle the key while watching the voltmeter. ~50year old truck that switch is probably in need of some TLC.

Also not sure if there Alt is the factory unit from the 360 or for the 460(which I think is from a 76/77 vehicle). 460 cruises about 2500rpm on the freeway and has been revved north of 4K quite a bit. Found literature that the 360 ALT has a max(engine) rpm of 2200, not sure how accurate that is as the door label max rpm for the 360 was 3000rpm.

I'm still in the process of diagnostics as time is limited to work on, and the truck is a cluster of splices and wire hackage.

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MadJoe
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Re: Alternator output

Postby MadJoe » Mon Jul 17, 2017 7:35 am

MadMike wrote:
Also not sure if there Alt is the factory unit from the 360 or for the 460(which I think is from a 76/77 vehicle). 460 cruises about 2500rpm on the freeway and has been revved north of 4K quite a bit. Found literature that the 360 ALT has a max(engine) rpm of 2200, not sure how accurate that is as the door label max rpm for the 360 was 3000rpm.


That can't be true (not about the alt, I'm sure it quits being effective past 2200), but a 360 generates max HP at 4000 and can rev to 4500 - it isn't pretty, and it isn't getting you anything but more wear and less fuel, but it will do it - so that plate must have been for something else.

Or am I misunderstanding? Are you saying the Alt is maxed out at 3000? That could absolutely be true.

-Joe
1971 F-350 DRW SWB with OEM disc brakes & power steering, C6 transmission, and original cab corners.


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