Are car audio capacitors good or bad, and what’s the deal with them?

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A lot of people are probably wondering if they need to add a capacitor to their car audio system.

You might have heard that a friend added a capacitor to their system and it stopped their headlights from dimming or even experienced it for yourself.

So you think to yourself “Hey, my power system must be better off with a cap installed, it fixed my power issues!”

Well this is a double edged sword so to speak.

Yes, your headlights might not be dimming any longer but that does not equate to a healthy electrical system, nor does it mean you’ve solved your voltage drop issues.

Let’s take a look at what a capacitor is, what it is not, and how exactly it affects your electrical system.

(Oh and in case you’re lazy and want to stop reading here, the answer is NO. You do not need a capacitor and it will not help with your electrical system if it’s already under strain from your amplifier(s))

Capacitors: What they are and are not

Simply put, it is a device that buffers electrical current.

Yes, it stores power to an extent, but it does not function in the same way as a battery.

Capacitors are advertised as a way to store extra current and deliver it to your amplifiers when they pull large amounts of power to stabilize your electrical system and current draw.

That’s all good and well in theory but in reality it just makes things worse (kind of like “Trickle-down economics”).

Do You Need a Capacitor?

Before anything else, here are reasons some people install a capacitor, aside from dimming lights, which we’ll discuss more in a bit.

To Improve Sound Quality

The primary reason a lot of people install a capacitor is to boost their vehicle’s sound quality.

The truth is that audio amplifiers need extra power, and your car’s battery might not have enough juice to power your setup adequately.

Hence, a lot of people believe that an extra capacitor might do the trick to reach the voltage supply you need for those heavy bass beats.

To Prevent Heating Amp Systems

Is your car amplifier heating up? This usually happens during a sudden fluctuation in voltage because your amp is seeking more power from your battery.

There is a possibility you can meet the correct voltage rate needed with a capacitor, thanks to its fast charging and discharging of power.

The problem is that it can also cause an uneven supply of voltage for your vehicle.

To Support Electronic Products and Components

Are your electronic devices starting to malfunction? It may be caused by a decline in voltage.

Again, some people think that a capacitor can help them achieve a higher voltage potential. That’s not the case.

Keep in mind that a capacitor is not the same as a battery. Hence, you might want to install a secondary battery instead.

Don’t worry; we’ll talk more about this in a bit as well.

What makes a capacitor so bad if there are a lot of people who continue to promote and use them? Allow us to answer that in the next section below.

What happens when you install a capacitor

When applied to a DC current situation as in car electrical systems, capacitors will limit the voltage supplied to the amp (read bottle neck) and actually divert power away from the amplifier to other devices, hence the reason your headlight dimming magically went away!

Here’s a 4k ultra slow-mo video of a pair of headlights dimming when the bass hits (your graphics card may not be able to properly render the video though):


Anyway, keep in mind that your alternator is the source of your vehicle’s ability to generate power and does so at around 14 volts whereas your battery only supplies around 12 volts.

The idea is that when your power consumption has reached the point where your alternator cannot keep up, your battery will supply the additional power but it will drain quickly (this is why your lights are dimming in the first place), so when your vehicle is starved for power due to large amounts of current draw from an amplifier or any other electrical device for that matter, no amount of capacitors or extra batteries will improve the situation.

How to really fix the dimming problem

The bestand really only way to solve power issues is to add a high output alternator.

multiple alternators 4 high output alternators

You probably won’t need this many tho

“But!” You say; “I seen this dude who had a whole bank of batteries supplying his amps and his system was pounding”

That may be the case and many people add additional batteries to help supplement multiple amplifiers but I would venture to guess “dude” also had multiple high output alternators to supply those batteries with current.

The other reason people use multiple batteries are to power amps when the engine is off and the alternator isn’t running.

Here’s another reason capacitors are bad for your system: They can actually damage your amplifier.

Since capacitors have to charge, discharge and then charge again, they will supply uneven voltage to your amps which is not a good thing.

The idea is to supply at least as much constant current as your electrical system needs on average and have extra head room for when you really crank the volume.

You can only supply as much current as the most limiting device in your system will provide, that’s why it’s recommended to install a high output alternator AND do the Big 3.

There’s not much point in shelling out the cash for an upgraded alternator if your wiring won’t let all that extra juice flow.

A Viable Alternative: Installing a Second Battery

Do you feel that your existing battery is not enough to supply all the juice your car needs?

That’s probably not surprising, given the increasing number of electronic components you can install. These include coolers, portable refrigerators, extra lighting, and more.

This is also true for those who want to enter their cars in competitions or simply enjoy using their electronics when the car is not running.

Before you consider installing an auxiliary battery, you should first make sure there aren’t any underlying electrical issues needed to be addressed.

You don’t want to start the complex installation process only to find out later that the issues you were experiencing still persist.

Worse, you might find that you don’t need the secondary battery in the first place.

One common worry is that it might be unsafe to install a secondary battery. In truth, installing an extra battery in your car is safe, provided that you do it properly.

It is for this reason we don’t recommend you to DIY the process unless you are confident with your wiring and placement skills.

You can’t just install it anywhere, especially since batteries have a risk of explosion. On the other hand, it should be close to the component it needs to power, such as your amplifier.

In the end, it might be better to leave this project to the pros instead.

How To Connect a Capacitor

If you lack the instruction manual that comes together with the various capacitor types, it is paramount that you appreciate the danger posed by a cap. It could charge and discharge a lot of power rapidly. The discharged power can weld metallic objects such as jewelry and tools.

New caps usually come in discharged, making them safe. A wired light bulb or resistor often comes with the package of most inexpensive-yet-luxurious capacitors. Wiring the resistor or bulb across the terminals of the cap lets the capacitor safely and slowly discharge. If you wire it up differently, you can use the same resistor or bulb to charge the cap safely.

Like every other electronic installation in a car, begin by disconnecting the car battery ground cable. You will also need to remove the in-line fuse of the amplifier’s wire next to your battery.

Capacitors need to be mounted nearest to the sub amplifier using short wires. This is for the additional electrical charge to travel only a short distance before getting to the amplifier. Also, ensure to securely mount the cap to prevent it from becoming a hazardous flying object if an accident occurs.

Like most electrical components, there are two poles in a capacitor – the positive and the negative- and these must be clearly labeled. The positive pole connects to the positive power supply terminal that links to the sub amp’s positive connection. Ensure to use identical gauge wires as those the amp uses for power for even flow of electric charge. You can accomplish this using a distribution block.

However, in some instances, the cap has several connection terminals making it simpler to connect to the system. The various terminals serve as a distribution block. Therefore, for example, the power cable running from the battery terminals/current source connects to the positive terminal of the cap directly, while a short cable links from there to the positive power terminal of the amp.

The capacitor’s negative terminal connects to the chassis ground as in the amp. It is recommendable for the ground and amp to share the same bolt. Ensure to crap off all the paint around the location of the chassis ground that would make it a bad ground, and that all connections are tight and clean to avoid having a faulty ground. You will then need to charge the capacitor. However, be careful not to do it too quickly as a rapid electrical charge destroys the cap.

Wrapping up

There are only two reasons that people will tell you that you need a capacitor in your car audio system and they are:

The person doesn’t know what the hell they are talking about OR they are trying to sell you a capacitor.

So let’s review: Alternator good, battery good, capacitor BAD.

Alternator good battery good capacitor bad

I think that about sums it up but if you have any questions or need a nerdy, long winded technical explanation, feel free to leave a comment below and we’ll be happy to talk in extremely dry, electrical engineering speak.