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Understanding Alternators

Click here for our extensive guide, "How does an alternator work?"

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Do I Need a Bigger Battery Wire to the Alternator?

Battery Wire Size and High Output Alternators

When upgrading to a higher output alternator you should always install a larger wire between the alternator and battery . Even with a standard output alternator you will get better performance and life out of your alternator if you upgrade the main battery wiring. The original wire just isn't large enough for proper power transfer. If you are using your alternator to it's maximum output or when you upgrade to a higher output Alternator you must increase the wires size. An alternators ability to send the power it is making to the battery is directly related to the wire size and quality of connection between the alternator and battery. Also, a wire that is to small when used on a high output alternator can cause the power to back up within the alternator making it overheat, burn up and fail.

Another area that little is paid attention to is the ground. You must also improve the ground as well. A poor ground will hinder the alternators ability to send power to the battery and can burn an alternator up just as fast as an inadequate alternator to battery wire. Your ground may be fine when you first install your alternator but over time corrosion and resistance builds up in the ground connections. This is why it is best to run the ground directly from the rear of the alternator to the battery.

Here is another great auto electric tip from National Quick Start Sales on upgrading the wire between the alternator and battery. Randy says, you do not need to rip out your old wiring when upgrading. You can piggy back a second wire between the alternator and battery. The main battery wire connected to the back of the alternator has power to it at all times, even when the vehicle is shut off. You connect this wire like normal then you run a second wire between the alternator and battery. The power coming out of the alternator will treat the two wires as one, power follows the path of least resistance.

On a safety note, when running the second wire you should fuse it near the battery. The fuse is just in case the wire gets pinched or shorted out, the fuse will blow instead of the wire burning up. You should use the largest fuse you can for the wire size, fuses are restrictive to current flow. Typically you want the fuse value to equal 80% of the wires load carrying capacity.

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What is a Self Exciting One-wire Alternator?

The Difference Between One-Wire, Two-Wire, and Three-Wire Self-Exciting Alternators

A self exciting or "One wire" alternator as it some times called, has only one wire running to it., that one wire is the main large battery wire. Don't confuse one wire because the plug going to the alternator only has one wire to it, this is a two wire system. The one wire, self exciting alternator uses a special voltage regulator that doesn't need an ignition wire to activate it.

This type alternator only requires a battery wire hooked to it. The voltage regulator contains circuitry that uses the residual magnetism in the alternators fields to determine when to turn the alternator on , the regulator does this by sensing the RPM the alternator is turning. When the alternator gets to a certain rpm the voltage regulator "turns on". Typically you start the vehicle, rev the motor slightly then the alternator starts charging. This type alternator is commonly used on custom cars, trucks, tractors and other non standard applications when wiring is a factor. In choosing this type alternator you must consider, do you want to rev your motor slightly to get the alternator to turn on. Also, when using the self-exciting alternator on tractors or other slow turning motors does the engine have enough RPM's to start the alternator charging. This can be overcome by using a smaller pulley or by adding an ignition wire. Is another name for the Self-Exciting Alternator mentioned above. You only need connect the battery wire (one-wire).

Two-wire Alternator:

Most standard and all self-exciting regulator alternators will work using the two wire setup. Two wire means that you use the battery wire and an ignition wire to activate the alternator. With this setup the alternator starts charging as soon as the engine is running.

Three-wire Alternator:

This setup uses a battery wire, ignition/warning light wire and voltage sensing wire, Three wires.

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Do I need to change my voltage regulator when using a high output alternator?

Voltage Regulators and High Output Alternators

When you upgrade your existing alternator you shouldn't need to upgrade your voltage regulator. When upgrading to a high output alternator you rarely need to change your voltage regulator. The voltage regulator controls the alternator output by sending power to the rotor (field). The rotor spins inside of the stator, the reaction between the rotor and stator is how power is induced within the stator. The voltage regulator senses the battery voltage, if the battery needs more power the voltage regulator sends power to the rotor coil turning the alternator on. If the regulator senses that the battery or system needs a lot of power it sends maximum voltage to the rotor making it a big electro magnet thus causing the alternator to produce maximum power. If the regulator senses a small need at the battery it will send minimal power to the rotor causing the alternator to produce little power.

Never does the alternators amperage go through the voltage regulator. The area of concern when changing to a high output alternator is the amperage draw of the rotor. The voltage regulator does have a field amperage rating and because it has direct contact with the rotor you must be concerned with the amperage draw of the rotor. If the amperage draw of the rotor is greater than the rating for the voltage regulator the regulator will fail.

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How do I get more power at Idle?

Improving Output at Idle Speed

There are several ways to get more power at lower engine speeds. If you only require a little more power at lower engine speeds you may be able to use a smaller pulley. The smaller pulley turns the alternator faster at lower speeds thus making more power. When using a smaller pulley care should be taken not to over rev the motor. If you over rev the alternator with a smaller pulley the alternator can fail.

The best way by far to obtain more power at lower engine speeds is to install an oversize alternator. The physically larger alternators produce more power at lower engine speeds and are much more reliable at higher outputs. Installing a higher output alternator that is the same size as your original alternator will not give you more power at idle.

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My GM or Ford Alternator Does Not Work, What Now?

Troubleshooting Your GM or Ford Alternator

There are several things you can do to get to the bottom of a non-working alternator The first thing you should look to is the ignition wire that activates the alternator. Both Ford and GM, as well as most Import vehicles, us some sort of ignition wire. This ignition wire is fused so to check for a blown fuse turn the ignition on and check the ignition wire to the alternator. It should have power when the key is on an no power with it off.

• Check battery: You must have a good battery with good connections for an alternator to work properly.
• Check belt: Your belt must be in good condition and properly tensioned.
• Battery Cable: The cable between the alternator and battery must be properly matched for the amperage alternator. If you are running a higher output alternator you must have a larger cable. We have found the even the factory cables are not large enough for standard output alternators. You should also consider running a separate ground cable from the alternator to the battery for better efficiency.

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How Much Engine Horsepower Does an Alternator Take?

Horsepower Requirements for High Output Alternators

How Much Horsepower does an alternator take?

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What Battery Wire Size Do I Use?

Battery Wire Size and High Output Alternators

Battery Wire Size Chart

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How Do I Wire a GM (Delco-Remy) Alternator to Make It Work?

Wiring 10Si, 12Si, 15Si, 17Si, and 27Si Series Alternators

General Motors has only had 4 different series alternators since it first replaced generators with alternators in the 1960's. The very first alternator was the 10DN externally regulated alternator. The first internal regulated alternator was the 10Si series starting in the early 70's and used till the mid 80's. These alternators were quite popular for auto, truck, industrial, marine, farm and adaptive applications. Since the introduction of the 10Si, GM's Delco-Remy line has offered the 12Si, 15Si, 17Si, 27Si then the CS and AD series alternators for cars and light trucks.

This first section will cover wiring information for the SI series only, we will go over the CS and AD series wiring later. Although they may vary in size and output, the wiring is the same for all the Si series. Wiring these alternators is quite simple. All the Si alternators can be considered both 2 and 3 wire systems. To activate these alternators you are only required to supply the main battery wire to the (BAT) terminal which must have power on and an ignition wire to the #1 terminal. Most all the Si series alternators should have two spade terminals, but some that have three terminals, the third is for a tachiometer connection and senses the alternator RPM.

Near the spade terminals, the rear housing should be marked #1 and #2. Some aftermarket housings are not marked and others may be worn off. So if your alternator housing is unmarked, look from the rear of the alternator: the #1 terminal is on the left and the #2 on the right. You only need an ignition wire to the #1 terminal to make an Si series alternator work. The #2 terminal is for voltage sensing, and is optional. The #2 voltage sensing terminal allows the voltage regulator to sense the battery voltage so it knows when to turn the alternator on and off. The #2 terminal, if it is not used, causes the regulator to revert to internal sensing and pick up the battery voltage at the main battery wire on the back of the alternator. Some alternators are wired with a jumper from the #2 terminal directly to the battery connection at the back of the alternators, but this is not needed.

The ignition wire to the #1 terminal can be supplied in two ways, either a direct ignition wire from the key switch or through a light bulb. Running the ignition wire through a light bulb before connection to the alternator will give you a warning if your alternator fails to start charging or if it quits working while the engine is running, this is commonly known as the idiot light. Another thing that should be mentioned is the #1 terminal must be ignition switched. I have heard of situations where a wire was run to the #1 terminal that had power on at all times. What happens is when the engine is turned off the #1 terminal switches to ground which over time can burn up the voltage regulator or the wire if power is not cut to the #1 terminal. Another note for special installations of the Si series alternator is that in some cases when you try to shut the vehicle off, power to the #1 terminal from ground to positive power, the positive power feeds up to the coil and keeps the vehicle running. To cure this you must install a diode in the ignition wire that activates the #1 terminal. The diode will stop the power from feeding back up the ignition line.

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