Ford 8000 alternator 55 amp vs 72 amp

[benterryfarm]

I have aftermarket A/C on my ford 8000 cab tractor. With the tractor running the alternator shows 14.2 volts, tested at the alternator. The battery also shows 14.2 volts. Once the switch for the A/C is engaged the battery voltage drops to 12.2 volts, and eventually after many hours of use the battery gets drained to the point that the next time I turn the key to start it it won't start.

I'm not 100% certain but I think the alternator on my tractor is a 55 amp, as it is a 1969 8000. My question is whether or not the 72 amp alternator used on later models will be a direct replacement for my 55 amp. I feel the additional output will solve my issue. The A/C compressor is belt driven, the fans and controls require juice from the alternator.

My second question is, even if f the 72 amp is a direct fit are the current wires on the tractor of a suitable gauge to be able to handle the additional amperage?

 

[Ozlander]

Tighten the alternator belt. If that doesn't help, get a new belt.

 

[Hobo,NC]

I have aftermarket A/C on my ford 8000 cab tractor. With the tractor running the alternator shows 14.2 volts, tested at the alternator. The battery also shows 14.2 volts. Once the switch for the A/C is engaged the battery voltage drops to 12.2 volts, and eventually after many hours of use the battery gets drained to the point that the next time I turn the key to start it it won't start.

I'm not 100% certain but I think the alternator on my tractor is a 55 amp, as it is a 1969 8000. My question is whether or not the 72 amp alternator used on later models will be a direct replacement for my 55 amp. I feel the additional output will solve my issue. The A/C compressor is belt driven, the fans and controls require juice from the alternator.

My second question is, even if f the 72 amp is a direct fit are the current wires on the tractor of a suitable gauge to be able to handle the additional amperage?

The drive system for the alt is in question and the easiest to address.

I don't know the drive aspect of your tractor on the automotive side the best I remember its 3 to 1. Using the automotive aspect the alternator is designed out put max amperage at 3000 RPM. When testing amperage to confirm the alt is producing proper max output if its with end 10% of rated output its good. If its a 55 amp alt it would be good to go at 49 amps. Its hard to see where your AC is pulling more than 30 amps then add in 5 amps to run everything else that leaves 14 amps to charge the battery back up. Anything under 1000 RPM your are going to be below break even point.

If you use the same aspect ration a 72 am alt will get you about 10 more %. On the automotive side as the higher amp alt's became the norm the aspect ratio increased. The reason being to bring the max charging rate RPM down closer to 1500 RPM.

If I had it in front of me I would fully charge the battery and load test it. Once I confirmed the bat was good to go pull out a amp clamp and test the alt for max output. There is some in between checking that's the basic test if it passes with flying colors its not the bat are alt. You always remember that one that gotcha the pulley was not tight on the alt : (. Maybe some of this rambling will help ya get closer to your issue.