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My new custom AC unit is killing the battery. I saw the batt go from 13.1V to 11.5V as I turned on the headlights and AC unit. I'm also in the process of installing some light bars on the rack. Thinking a 120A alternator should do. Single belt. Any recommendations?
Last edited by Rafael Suarez; Dec 10, 2024 at 09:38 AM.
Reason: typo
Where the reading at idle or was the RPM up to 2500+ when you took the volt reading?
Reading should be taken at RPM as the old system did not put out a lot at idle.
You know I have never seen what the volts are with AC and head lights on? I can tell you if I first start the truck I do see the lights dim at idle but after the battery recovers from starting no more dining lights.
Now if you want to do a ALT upgrade to the 3g there are posts in here that can walk you through it.
Note you will have to replace wiring and un-wire the AMP gauge or get it rebuilt to read volts by Rocket Man.
Good luck
Don't get too upset if you put your high output alternator on the truck, and then you end up with chronic belt squealing. Some people have this problem, some don't. But a single v-belt only will support so much load. You will notice when Ford went to a 130 amp alternator, they also went to a wide serpentine belt.
added thought going off of Franklins post above.
I thought I read somewhere on here, that a v-belt is good up to about 100 amps and after that you need serpentine.
Don't get too upset if you put your high output alternator on the truck, and then you end up with chronic belt squealing. Some people have this problem, some don't. But a single v-belt only will support so much load. You will notice when Ford went to a 130 amp alternator, they also went to a wide serpentine belt.
Where the reading at idle or was the RPM up to 2500+ when you took the volt reading?
Reading should be taken at RPM as the old system did not put out a lot at idle.
Good luck
Thanks, I don't own a tachometer.The furthest I got was the OBDII. I already don't have any space for the hardware tools. 🤷♂️ gotta see if someone around here does ol' timey electrical.
I'm about to do a 3G on mine. I did it on a 79 I had and didn't have any squealing issues, I didn't have AC though but had a MkVIII fan that probably didn't draw as much. LMC sells some upgraded single wires. My 80 has dealer AC, the alternator is single V but the AC is double V. There are also serpentine belt conversion kits, There might also be double V kits out there too.
I would just do a 3G swap and see how it goes, then worry about squeal IF it happens.
Thanks, I don't own a tachometer.The furthest I got was the OBDII. I already don't have any space for the hardware tools. 🤷♂️ gotta see if someone around here does ol' timey electrical.
You dont really need a tach just know when checking old car & truck charging systems for voltage you need to bring the RPM up off of idle as they dont put out much at idle.
So if you have everything turned on and at idle got 11 volts if you were to bring the RPM up if the system is working you should see 13.5 to 14.5 volts and your head lights get brighter and maybe the blower fan faster. This is normal. This is why back in the day if people did not drive their car long enough at speed the batteries would go weak. They get a jump bring to garage they charge battery and check the system & battery and all is good for a week or so and it is back.
Come to find out they only drive about 5 miles with head lights and heater on and they stop at a store for coffee and shut it off, so they never recharge the battery on the drive to or from work.
Originally Posted by GOVTMOD
I'm about to do a 3G on mine. I did it on a 79 I had and didn't have any squealing issues, I didn't have AC though but had a MkVIII fan that probably didn't draw as much. LMC sells some upgraded single wires. My 80 has dealer AC, the alternator is single V but the AC is double V. There are also serpentine belt conversion kits, There might also be double V kits out there too.
I would just do a 3G swap and see how it goes, then worry about squeal IF it happens.
Some install a soft start regulator in the 3G ALT it brings the ALT on slowly so the belt is not under a "shock" load.
As for the 1 wire ALT I am not a big fan of them. I seen to many posts in a old car forum I am a member of were the person installed a 1 wire ALT and the battery dies in short order and when checking find the ALT is not putting out?? They get a replacement and the same thing happens
Come to find out the 1 wire gets it feed back to charge for the "B" post on the ALT and not from the battery like the factory dose.
The ALT sees it is putting out the right 12.6 volts but it really needs to be 13.5 - 14.5 to put power back in the battery.
If you check where the factory sensor wire is, it is on the main feed wire into the car so the battery gets charged.
You also have to watch some of them 1 wire ALT as the RPM has to get over 3000 RPM before it will kick in the need to start charging.
Dave ----
I would just do a 3G swap and see how it goes, then worry about squeal IF it happens.[/QUOTE]
Originally Posted by GOVTMOD
I'm about to do a 3G on mine. I did it on a 79 I had and didn't have any squealing issues, I didn't have AC though but had a MkVIII fan that probably didn't draw as much. LMC sells some upgraded single wires. My 80 has dealer AC, the alternator is single V but the AC is double V. There are also serpentine belt conversion kits, There might also be double V kits out there too.
I would just do a 3G swap and see how it goes, then worry about squeal IF it happens.
Thanks,
Funny, after all the years I've been on this site and over there, I found that link today. I should really spend more time under that "documentation" link...
The other funny thing about that, I was actually trying to find something else for another thread I was reading on here.
