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What are high output alternators?

2JZ High Output Alternator

When a vehicle ships from the factory, it comes with an alternator that meets the basic needs of a car’s electrical systems. Although there is some wiggle room with the factory charging system, the addition of speakers, subwoofers, infotainment systems, and other energy-draining components can result in dim headlights, poor audio performance, and other problems. The solution to install a high output alternator.

Although there are a few ways to deal with a shortage of power (including additional batteries and stiffening capacitors), a high output alternator is the only way to address the problem. These high-powered units put out higher amperages than factory alternators and are available from aftermarket manufacturers, rebuilders, and OEMs.

What Qualifies as a High Output Alternator?

Since factory alternators aren’t uniform in terms of power output, the term high output alternator is going to be relative to the original amperage rating of a vehicle. To qualify as a high output unit, an alternator needs to provide more amperage than the factory unit that it replaced. That means there is a big difference between a high output unit that provides 100A at idle speeds and a water-cooled unit that provides upwards of 350A. There’s also a difference between simple re-winds and units that are remanufactured from the ground-up.

Why Factory Alternator Amperage Output Isn’t so Hot

The first alternators blew older dynamo generators out of the water in terms of raw amperage output. However, the electrical systems that they had to supply in the 1960s were nothing compared to the electrical systems today. Many early factory alternators were only capable of putting out a maximum of 30A, which is a number that many modern stock units beat at idle speeds.

Today, a typical OEM alternator in an average passenger car or light truck can put out somewhere in the neighborhood of 50-80A. However, there’s a variation from one application to another.

The rated amperage refers only to its output at 6,000 RPM, which is why a 108A alternator may only put out 40 or 50A at idle speeds.

Who Needs a High Output Alternator?

Stock units are designed to meet the needs of the electrical systems on the vehicles that the units ship with. Because most people don’t make significant modifications to their vehicles, most drivers won’t need a high output alternator. So, how can you tell if you need to replace a factory alternator with a higher-powered aftermarket unit?

One sure sign that an alternator is underpowered for its application is if it burns out too fast. If you go through alternators on a regular basis, your unit is probably running right up against the ragged edge at all times, which can cause undue wear.

Even if your vehicle is more or less stock, install a high output replacement alternator if you are in the shop for electrical problems regularly. Since some vehicles ship with multiple alternator configurations, you may be able to find a direct-fit, original equipment replacement unit.

When Enough Isn’t Enough

Although a vehicle’s electrical system is fairly complicated, you can get a good idea of whether you need a high output alternator by performing a few calculations. For example, wattage is determined by multiplying amperage by voltage, so an 80A alternator is capable of putting out:

80A x 13.5V = 1,080W

That’s plenty of power for any factory sound system. However, if you add amplifierssubwooferssubwoofer amplifiers, and other power-hungry components (on top of everything from headlights to a cooling fan), it’s easy to see how you might need a high output alternator.

It’s also important to remember the difference between idle output and rated output. If the rated output of an alternator is 80A, it is only capable of delivering that much amperage when the engine is revved up. Both ISO and SAE standards use 6,000 RPMs to determine the rated amperage of an alternator, which roughly corresponds to 2,000 to 3,000 engine RPMs.

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High Amp Alternator

High Output Alternators provide the current you’ll need for LOUD car audio

To avoid the dreaded red light of despair in the suddenly silent night, you will need to upgrade your electrical charging system. High Output Alternators provide amperage that your stock alternator cannot produce.

If the Big Three Wiring Upgrade failed to alleviate your electrical issues in your car or truck, then upgrading the alternator might be your next step toward a high performing car audio system.

Did increasing the current flow through the system solve problems like headlight dimming or did it make them worse?

This is because your amplifier is trying to draw more amperage than your stock electrical system can create.

Boosting the flow of current in the vehicle will only increase the problem if the charging system can’t keep up.

This means your headlight dimming could worsen after upgrading your electrical charging systems wiring. That is if the alternator cannot supply adequate power for both your cars electrical charging system and stereo.

High Output Alternators increase the amperage of your system.

Relying on a stock electrical system for the massive amperage that car audio amplifiers require, while still supplying your vehicle with the current it needs will result in low voltage and other problems.

When the alternator can’t provide the necessary amperage for your system, the battery tries to make up for the amperage deficit.

When the battery cannot make up that deficit, the power supplies fail and the amplifier goes into protection mode.

Stock electrical charging systems typically fail to provide the level of current that 2,000 Watt+ car audio builds require.

Wait, wasn’t that what the Big Three was for?

Upgrading the Big Three is the first step toward a solid electrical system.

It increases the diameter of the straw our current flows through.

Adding a high output alternator is the second step. It increases the force of water that flows through the straw.

There will be costs to keep in mind and hurdles to overcome.

Depending on the current your vehicle and install require, you may need to make modifications to your engine and create space for a small power plant under your hood.

If you’re chasing numbers, prepare to play Tetris in your engine bay to make room for the alternators and the bracket that will be holding them. Championship rings don’t come easy or cheap.

If you’ve read this far and are starting to rethink 150’s, hair tricks, and broken windshields, you can still enjoy considerable bass with a single high output alternator in your car or truck.

As a general rule, you need about 100 amps of current for every 1000 watts of power generated. Add that to the base electrical requirements of your vehicle for the total amount of amp-hours you need for your system.

You can use this formula: watts/volts = amperes

Example: You plan to install a 2,000 watt amplifier. Your vehicle’s voltage is 13.5 volts. Divide 2,000 watts by 13.5 volts. The result is 148 amperes of current. If your stock alternator output is 85 amps, add 150 amps for a total of 235 amps needed to safely operate the amp.

How to choose a High Output Alternator

There are a number of reputable manufacturers to choose from. As a starting point JS Alternators  is popular. We do not advise buying an alternator on eBay.

The difficulty is that one size does not fit all and many high output alts are vehicle specific.

Your alternator’s rated output will typically refer to the amperage output at high-RPM’s like highway speeds. When you’re idling, or running at a low RPM, your alt may only be capable of providing a small fraction of that rated power.

The best practice is to do some research on what works for your specific vehicle.

Learn what hangups may be associated with that. Like what is ‘too much’ for your engine, how much amperage does your car or truck need to operate, and determining the best use of your available space.

For instance, if you have an economy car, you may be limited to 300 amps or fewer. Vehicles with small engines may not be able to effectively operate alternators larger than 300 amps.

You may find your engine dying when idling if you are using too much amperage.

It is a balancing act. Check the data available for your vehicle, your desired application, and then read the reviews.

Many High Output Alternators are made to order, so you’ll have some time on your hands while you’re waiting for it to be manufactured and shipped.

Every alternator installation will be different. Follow your manufacturer’s instructions to install yours. Don’t be afraid to ask them questions.

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XS Power Wattage Chart


Choosing which battery to use to power your audio system can be daunting when faced with all sorts of numbers and specifications that don’t seem to have anything to do with car audio at all. With our wattage chart below, the choice has never been easier! When using only one battery, refer to the “Primary” column; when using a second battery as a supplemental battery, refer to the “Secondary” column. When replacing the original battery and adding supplemental power, use a combination of the two columns to arrive at the desired level of power needed to satisfy any stereo system!

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Should I Upgrade My Alternator?

2009 - 2010 Ford Mustang High Amp Output Alternator

What Does the Alternator Do?
Alternator Basics:

Alternators keep your vehicle running after the starter kicks over the engine
Alternators are rated in amps, so the more accessories you add with a higher draw (like an aftermarket sound system) the more powerful alternator you’ll need
Although underdrive pulleys help out supercharged Mustangs, the pulleys hinder your Mustang’s alternator. If you’re thinking about a new set of pulleys, don’t neglect your alternator
A weak alternator can put your electronics on the fritz, throw engine codes, make your lights flicker, and cause your Mustang to shut off while cruising down the road
Surplus energy isn’t a bad thing, so getting more amps than you need isn’t a bad idea
Your Mustang’s electrical system relies on the alternator to keep it running. Once the battery starts the car, the alternator takes over. It recharges the battery and keeps all the electrical components of the car juiced up and working properly. If your alternator is not working properly or is undersized for your needs, the car’s systems will not be working at their peak performance. This can lead to a poorly running vehicle and dimming or weakened accessories. On some Mustangs, a weak or faulty alternator can cause many electrical gremlins that result in incorrect trouble codes and diagnoses.

Continue reading Should I Upgrade My Alternator?