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”).
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 best and really only way to solve power issues is to add a high output alternator.
“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.
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.
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.