I have always noticed that my lights would be dim at idle. I just had the ALT rebuilt and was doing some testing and I installed a digital volt gauge.
With engine at idle it charges to 12.2-12.4 volts with head lights on.
If I run the heater on high,with lights on, it steadly drops voltage till it gets to 11 volts. turn off heater or lights and it will go back up to 12.2 volts.
Specs on truck:
81 f-250 S-cab,4x4 trailer special.
ps,pb,cc,ac
300-6(modded), t-19 originally 351m/c-6

my question: What is the factory AMP rating for the altenator?
It has a 38amp on it now(seems small to me)
I have a junk 81 f-150 that has a 40amp on it.
A 69 f-100 with a 60amp on it.
Those 3 are small rear termainal altenators.
My brothers 83 f-100 has a 101amp side termainal altenator on it, we havent run it yet.
Thought I scored a 101amp ALT side termainal off a 79 lincoln but after getting it off(cutting off, frozen 7/16 bolt) it is a 70 amp.
Is it worth trying the 60amp?
Fitting the bigger side amp ALT, and getting a 101amp for it?

I will be using a 9k winch to winch car on trailer this race season as i'ved switched to a low base pressure/CW clutch and cant drive it on.

Thanks for the help....................Ron

 

I think there were at least two available (60 & 70) it depended on options installed + the
model & configuration of truck.

I've heard of a 40-amp but don't think I've ever seen one installed.

I haven't attached at volt meter to an idling engine in a long time but that sounds low to me....

 

The voltage will vary significantly depending on where you tied your volt meter in. If it is tied into the wiring in the dash you are reading the voltage after a lot of 30 year old wiring, fuses, and connectors. All of that has resistance, and when you bring the blower motor on you pull more current. E=IR. Translated that means the voltage, in this case the voltage drop from battery voltage, equals the current (I) times the resistance (R). Therefore, the voltage you read will be lower than battery voltage, and it isn't unusual at all to see 11 volts inside an old vehicle when running significant current - and both the headlights and the heater motor pull significant current - and the engine at idle.

But, no reasonably sized alternator will give you enough current at idle to run the winch without pulling power from the battery. The alternator needs to be spinning faster in order to provide maximum output. One trick would be to install a relay such that bringing the winch on would energize the idle speed solenoid that many of the trucks have if they are equipped with AC. That would give you more RPM and more juice.

 

If you get a gigantic alternator to run all that as I plan to then plan to upgrade wiring from alternator to battery.

 

Is your idle speed up to spec? I would run it around 800 rpm since you have a manual tranny.

 

I would get rid of the external regulated alternators all together and just do a 3g swap. Do a forum search, there are a couple of really good post on it. Regardless you will have to do a wiring upgrade.

 

Truck belonged to a pulp wooder so it wasnt very well maintained. Fixed it just good enough to keep it going.

 

I'm sure it had a bunch of mixed up parts on it.

 

Yes it had some ALt wiring issues in the past and I replaced most of it around the ALT and REG. Will look at the other wiring and connections and possiably do a relay system to headlights.

 

Yes with the 268 H cam it needs idle around 800 or so, but you know how them hollys change with the weather.lol

 

I read the post on this upgrade after I posted and this maybe the way I go when I send my mustang to the paint shop. I've got some other stuff to do but may find time to get to this. Fortunately it will be getting warmer here in SC soon so I wont need the heater, but will still need it for the winch. I can idle it with the manual choke cable. thanks

 

My neighbor has a TJ Jeep we've done a lot of work on, inc installing an 8K Warn winch. He's a Tulsa police officer and they paid him gas and mileage all last week to use it as his patrol car. Says he's pulled "hundred's" of cars out of the snow with the winch and never had a problem with not enough power.

I'm sure the Jeep has a bigger alternator than yours, but it only has one battery - albeit a new one although rather small. He says if he keeps the engine running there is no problem.

As for the volt meter, if what you really want to know is the state of your battery you should run a wire from the meter to the battery, although stopping at the solenoid would be almost as good. But make sure you put a small fuse, something like 1 amp would be fine, in the line as soon as you come off the solenoid.

 

Standard altenator was 40 amps.

Optional was 60, 70, and 90 amps.

The highest optional altenator for 1980-1983 was 70 amps.

 

Thanks for that! Maybe I'll remember it for next time.

 

I just put a new one in yesterday, it's 65amps. My choices at the parts store were 60, 65, or 70.