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 (I think 8600, possibly 8700) 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?

 

[Bern]

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 (I think 8600, possibly 8700) 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 72-amp alternator did not arrive until the TW series came out in 1979. Although I have not tried it myself, I do believe it would be a direct bolt on. The regulator might be a different story however. Again, I'm not positive because I've never tried it myself.

The existing wiring would likely be a little undersized. Rather than replace the harness or even the output wire, I'd simply run a 10-gauge wire in parallel with the existing wire between the alternator output terminal and the battery post on the starter.

All that said, the 55-amp version should be able to keep up just fine, unless you're running at night with the lights on, and/or you have some sort of an attachment that is drawing considerable current.

 

[Keith Williams]

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 (I think 8600, possibly 8700) 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 readings you are getting are classic signs of a slipping belt. Is your belt tight and in good condition?
A loose or glazed belt will slip as soon as a load is placed on it. The Alternator will stop charging and you will see the Voltage drop.
BTDT many times.
Keith