Selecting The Right Alternator For Your Tbird

(1) Electrical systems are always figured the same, even in your house. Simply put, the first statement about this in the National Electrical Code is that the supply MUST meet the demand. Then they de-rate ampacities to give a 20% safety factor in each branch circuit. Your car is no different except that car wiring is not hidden in walls, the environment vibrates and wiring is exposed to extreme heat, cold and harsh chemicals.

Start by adding all your accessories. (Everyone's car is different.) Consider battery losses when cold and 'sitting for days or weeks', electric fuel pumps, trailer hauling, inverters, stereo systems, headlight upgrades, iPad's, Cellphones, etc. Now look to the future and always consider this question, 'what do modern cars use?' If your system becomes inadequate by adding something like EFI or an electric fan you will be buying a bigger alternator very soon.

Are you planning on an electric fan? If so, get an alternator with at least 130-amp output because at idle speeds your charging system needs to sustain 25 amps or more, depending on the size of your fan, so it doesn't drain your battery. You see, it's not the total output that is important, it's idle speed output. Small alternators, like the 75-amp that came in my '90 Mustang, don't put out enough to run an electric fan when the car is just sitting. There is nothing worse than a system that drains the battery while the engine is running. With a 75-amp alt, there isn't enough idle-speed amps but there is with a larger alt.

Never depend on the battery to deliver power that the alt should have produced. I tried running a 75-amp alt with an electric fan. During the Woodward Dream Cruise our cars are in a big parking lot for miles, all day long. It ends up where the electric fan cools the engine but the alt is too small to charge the battery AND run the fan at idle. So, the battery drains and I'm looking to get off Woodward so I can run the car at 40-mph to shed heat and charge the battery. Now, I have a 130-amp alt and all is very well. Maximum amps mean very little. The most important question is, how many amps does it put out at idle speed?

Your modern car can live in stop and go rush hour traffic all day long (with the A/C on) without draining the battery. The alt you buy for your Squarebird needs to have the same capability or you might end up buying this system twice.

Squarebirds are notorious for over heating. An electric fan will shed a lot more heat than the mechanical fan but it needs an adequate alt.

I don't like one-wire alt's because they don't produce power until the engine revs up to around 1,500-rpm's. High rpms is how the alt senses your engine is running because there is no key switch 'sense' wire. Bottom line: Go get a regular 3 wire alternator that produces at least 130-amps. One of those 3 wires is a ‘sense’ wire that comes from your "Gen" light. This tells the alt that the key is on under normal operating conditions. If your alternator has quit working, or has thrown a belt the GEN light shines brightly so that idiot light does far more than you think. When your car was original, it showed the Key Switch was turned on, the engine was not running, the light bulb was ok AND it tickled the armature in your generator (which establishes proper polarity for the voltage regulator). You simply see it as a 'warning' or a test light.

One-wire alternators were popularized by hot rodders. They were never original equipment in new cars. I won't go into, 'why' because that is discussed all over the ‘net.

OEM alternators use a 'sense' wire for proper regulation. If you now have an alternator, you could change the dash light word 'GEN' to 'ALT’. The GEN wire IS a sense wire. It tells the alternator your Key Switch is turned on and it reports 'dashboard voltage' to the alt. With this voltage the alt can determine if the engine is running (or you threw a belt) and the bulb is good.

A one-wire alt may stop charging at idle speed until you hit the gas again. It compares battery voltage to charging voltage. So when current stops charging the battery it shuts off. Most importantly, when idling at low rpm, your 3-wire alt will still charge in a parade or serious cruise. As to whether you get a Ford or a GM alternator, I don't care what brand it is. Ford and GM alternators use the same shaft as the old generators. If you already have a double-belt pulley on your old generator, it's easy to swap on an alt.

If your original generator fails, consider changing to a modern alternator. Original low-output generators or early alternators and external regulators may cost more than a modern alternator (with an internal regulator). Alternator rebuild shops have hundreds of pulleys on the shelf, and our bone yards discard alternators daily, so they are inexpensive compared to hard-to-find original 35-amp generators. An early Ford 1G alternator requires an external voltage regulator. A 3G alternator is internally regulated. Keep in mind that some alternator mounting brackets, like the ones by C.R.A.P., only take Ford alternators. Also keep in mind that some alternator mounting brackets are said to be too flimsy to handle the torque of a high-amp alternator and can cause clearance problems or twisting of the mounting bracket under load.

Also consider the history and output progression of automotive charging: 1955 T-birds had a 30-amp 6-volt gen that output 180 watts. (30 amps times 6 volts = 180 watts.) 1956 T-birds had a 30-amp 12-volt gen that output 360 watts. (output doubled from one year before) Alternators became popular because they produced much more power at idle and low engine speeds. 1980's produced 75-amp alternators as more accessories were added. 1990's Ford cars came with 100 amp alt’s. Then 130-140 amps became common. In 2015, many alternators output 200 amps (200-a X 12-v = 2,400 watts; a far cry from the original 180 watts).

I've never heard anyone say, 'Dang, I wish I had bought a smaller alternator.'

Also consider the horsepower a modern alternator draws from the belt... 746 watts = 1 hp. 2,400 divided by 746 = 3.2 HP. <--this needs enough belt surface area or it will slip and squeal. That's why new cars come with a wide serpentine belt with so many ribs. You can do the same with a double-groove or a slightly larger diameter single groove pulley. All the old pulleys (Ford and GM are interchangeable) fit new alternators if you use the spacer behind the pulley (it looks like a ring) then tighten the nut and lock washer on the sheave of your choice. - Dave

(1) List of Ford Alternators to consider for mounting reference:

Ford Alternators

List of Alternator Mounting Brackets available: I understand this company's mounting bracket will also work on the 352 FE engine.

CVF Alternator Mounting Brackets

C.R.A.P. Alternator Mounting Brackets

March Performance Alternator Mounting Brackets

(1) Wiring a 130amp Alternator: #10AWG original wire is good for 30-amps, safely. A 130-amp alternator will burn up a #10 wire. Back in the day, #10 was ok because that is all generators produced.

This is a different ball game. Your wire needs to be at least three times larger than #10, which brings us to #2 AWG. I suggest you use WELDING WIRE because it is super flexible wire with hundreds of copper strands.

Alternators are solid state devices because they have diodes and SCR's. When they fail, they may short to ground. That means your alt wire will try to unload everything your battery has, dumping it to ground as fast as possible. The solution is a fuse. Don’t let the wire become your fuse.

A 150-amp fuse will work very nicely. If the alternator fails and blows the fuse, your battery will still have enough power to run your car for many miles. Mount the fuse on your fender apron and fuse the wire between the battery connection and your alternator. Remember to mount this heavy wire to something solid on both ends. Don't allow the lugs to be subjected to vibrations. You can strap one end to the alt bracket, leave extra wire between the engine and the fender apron, then secure the wire to steel a few inches before it terminates at the fuse. Those insulated steel strap loops work well.

150Amp Fuse Holder

(2) It can be bolted to the battery post of the solenoid and then to the alternator wire.

150Amp Fuse Holder

Legend: (1) Dave Dare ~ simplyconnected ~ Webmaster
(2) John Pizzi - jopizz ~Administrator


Created 7 June, 21015

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