High Output Alternator Car Audio Questions

When Does a Car Audio System Need a High Output Alternator?

high output alternator for car audio
Stock alternators usually have enough juice for aftermarket audio, but there are cases where a high output alternator is the only way to go. PieroAnnoni / E+ / Getty

Question: Do I need a high output alternator for my car audio system?

I recently upgraded my car audio system. New head unit, premium speakers, amp, big subwoofer, and I think maybe I went a little overboard because my headlights and dash lights keep flickering when I turn up the volume. Am I going to need to get a high output alternator, or what do you recommend?


From the way you describe flickering dash and headlights, it sounds like you’re dealing with a textbook case of an alternator that just can’t keep up with the demands that the electrical system is putting on it. Lights are typically the most visible sign of this since they tend to get dim or flicker when they aren’t getting enough power, but you can run into a whole host of other problems if the shortfall is great enough.

Power it Up

There are few ways to deal with flickering lights. The easiest fix is to just keep your volume at a level where the flickering doesn’t occur. Since the problem is that your alternator can’t meet the demands of your amplifier at high volumes, simply keeping the volume down will allow you to avoid the problem while still enjoying the increased sound quality of your premium car audio installation.

If you have your heart set on cranking up that volume, then there are two other options. The first is to install a stiffening cap, and the other is that, yes, a high output alternator will probably solve your problem.

Capacitors Vs. a High Output Alternator for Car Audio

Since you’re only experiencing a problem when you turn the volume way up, a car audio capacitor may solve your problem. These devices are also known as stiffening caps, and they essentially act as a reserve tank that can provide a little bit of “emergency” juice during times of especially high demand. That basically just means that when your car audio system tries to draw more amperage than your factory alternator can provide, the capacitor makes up the shortfall.

See more about: Car Audio Capacitors

If a stiffening cap won’t do the trick, you just want to avoid overtaxing your factory alternator, or you start to experience flickering lights and drivability problems at lower volumes, then a high output alternator is probably going to be the solution that you’re looking for.

Some high output alternators are specifically designed for car audio systems simply because that’s where the market demand is. However, high output is high output. Whether a unit is specifically a “car audio high output alternator” or not isn’t as important as the actual amperage ratings. With that in mind, it’s important to know roughly how much extra demand your sound system is adding to the mix, which will allow you to select a high output alternator that won’t leave you wanting more.

High Output Alternator Car Audio Demands

In order to figure out roughly how much capacity your new alternator is going to need, you’ll want to determine how much extra demand your car audio system is adding to the mix. Although it isn’t perfect, the easiest way to ballpark this is to use the formula of amps x volts = watts. So if you added a 2,000 watt amp, assuming a nominal voltage of 13.5V, you’d be adding roughly 150A of demand to your electrical system. This obviously isn’t an exact figure, but it is a quick and dirty way to get the ball rolling.

If you want to be precise, you can find out how much amperage every component in your car draws, add in the needs of your new sound system, and use that to determine the necessary rating of your alternator. Of course, you can always just ballpark this too by checking the rating of the factory amp, adding on the extra demand of your car audio system, and then just use that figure to find a replacement.

Idle Output Vs. Rated Output

The last thought I want to leave you with is that the “rated output” of an alternator typically refers to the amount of current it can produce when you’re cruising down the highway at a high engine RPM. When your engine is idling, or really any time it isn’t held at a high RPM, it will only be capable of providing a fraction (sometimes less than half) of that amperage.

This is why you’ll typically notice a problem like yours when the demand is highest (the volume is cranked up) and the production ability of the alternator is lowest (idling in traffic or at a stop light.) With that in mind, some edge cases can get by just fine if they just turn the volume down whenever the engine RPM is on the lower end.

See more about: Alternator Output