A popular upgrade that many people add to their cars are power capacitors. These are devices that are mounted on the power cable near the car’s 12 Volt battery, or on the cable by the audio power amplifier(s). Their advertised purpose is to serve as “supplemental power supplies” to your car’s electrical system when needed. According to Kim’s Nissan of Laurel, a local Nissan dealer in Laurel, Mississippi, this can be important when you have a powerful audio system in your car that can drain the car’s battery when playing loud, deep bass music. Here’s the story.

What are they?

Car power capacitors are typically big cylindrical devices, about 3 inches in diameter and about a foot long, though other shapes are common. They usually have beefy positive and negative terminals and possibly a third remote terminal that turns an internal LCD voltage display on or off. If you were to look inside a power capacitor you would find rolls of metallic foil separated by a special plastic called “dielectric.” They are sold at many auto parts stores and on the internet.

What do they do?

It is important to know that capacitors aren’t “another battery.” They do not store electrical power like a battery does. What capacitors do is make the existing power supply “stiffer.” In other words, when a high demand is put on your cars electrical system, say when your audio system pumps out some powerful bass notes, the normally 12.6 voltage coming out of your battery will sag just a little bit. It may drop to let’s say 12.4 volts. With a good-sized power capacitor added to your electrical system, the 12.6 volts is stiffened or held at 12.6V so it can’t sag when your audio system needs power.

Why is this important?

With audio power amplifiers getting more and more powerful, some people are noticing that their headlights dim a little when playing deep bass music loudly. By adding the right size power capacitor, the car’s 12 Volt power supply is stiffened so their headlights don’t dim.

What size do I get?

The general rule of thumb is to put in 1 Farad of capacitance for every 1,000 watts RMS of total audio system power. There are some installers who advise larger capacitors, and there is nothing wrong with that. In fact, many see benefits with 2 or 3 Farads per 1,000 watts RMS. The larger the cap, the stiffer the power supply from the battery is.

Will it make my audio system sound better?

If you are using huge power amplifiers, adding power capacitors can help prevent the amplifiers from getting voltage starved and affecting the sound quality. But, it is important note that they don’t actually make your system “sound better,” it just prevents your power amplifiers from getting starved for power.

Conclusion

Do you need a power capacitor in your car? It depends, if you have a powerful audio system and you notice your lights dimming as the audio pounds out deep bass notes, then you probably do. If you have a standard audio system in your car, say one from the factory, don’t waste your money. A power capacitor won’t make your audio system sound any better, contrary to manufacturer’s advertising claims.