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”).

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):

Kidding.

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.

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.

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.

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.

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Are car audio capacitors good or bad, and what's the deal with them?
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7 thoughts on “Are car audio capacitors good or bad, and what’s the deal with them?

  1. This is completely against all physics of electricity. I am a sound engineer and I went to for both electronics and acoustics. Caps are very important to the balance of an electrical system in a DC environment. If you look at the insides of any good amp, you will find a shit load of caps on the power supply side of the board. YOu are right that caps make things worse for amp but only if there is not battery in the entire circuit. A battery is a natural balancer of all things electrical. As a matter of fact, the alternator that you say is the most important thing in a car, you are right but only if there is a battery in the circuit. If not, you’re lights will flicker because an alternator is not a steady stream of pure DC voltage like a battery is and will hurt your entire electrical system. They produce AC and convert to DC and that circuit is rarely pure. A battery is pure DC voltage. All 3 batts, caps and alts are needed to have a balanced electrical system and get enough power to your amps. The most important thing that is rarely talked about that is needed in respects to clean power is good connectivity. Amps that are closest to a power supply(Batt or Alt, not caps) create more power to the speaker and run cooler. Even using Ohm’s law in regards to power wiring and you know the correct gauge and length of wire, does not take into the effect of environmental physics. IE – Temperature of the air around the wire as well as the temp of the wire itself. As the temp of the wire goes up, the resistance increases and therefore needing a higher gauge. This also happens to batteries and alternators the more power they have to produce. They will heat up and not be as efficient as room temp. Alts work great in cold temps but batteries are the opposite due to chemical reaction physics of Batts vs metalerical physics of alts. All this points to one conclusion that is often missed, double the size of the wire that the math tells you to use and make all of them as short as possible. Connectors are also often missed as an essential part of this issue. High current systems need power connectors that are soldered using a torch(not a soldering gun) and not just a screw down connection of just a crimp. YOu can use those but you must also solder them. This will ensure a perfect connection that will not corrode over time or deteriorate due to high temps and humidity. Either way, the alternator is least thing needed to be upgraded in a system as long as you have array of batt and caps near the amp. Reason is simple, batteries store lots of powers as well as create power (yes they create power using a chemical reaction which is why if you crank an engine till it wont anymore and then wait a little while you are able to crank some more) but discharge their power very slow, Alts create power, do not store it but push more power than a battery can per second, caps only store but can discharge thier all thier power in literally milliseconds which is why they can be dangerous but are extremely efficient because of thier very low internal impedance. Point being, batteries can be charged by any source if you alt cant keep up like a home charger. You can also let you car run for a while to be sure your batteries are charged if you know you were draining more than the alt can push out to charge them. It’s just math and you cant get around it. Batteries are the most important part of a high powered car audio system by far. As a matter of fact, I blew my alt a long ago when I was traveling and was about 500 miles from home. I couldn’t just replaced it because it was a high power aftermarket alt and I needed to get it fixed. I turn off everything possible in my car and kept driving just using my 5 Kenetik AGM Batteries and 30 farards of caps and they got me home easily and the voltage never got below 11.9 after the 500 mile trip.

  2. Nice opinion, but the capacitor acts like a small battery just for those short burst of electricity that your chemical battery can’t sustain. A good cap will save on your battery, alternator and sustain an even flow of current. It does not take current away from your amp, that would be a resistor. How could it if it’s in series? I just don’t understand how you got it so wrong. Maybe you bough a $20 cap and marketed 2 Farad but was really 0.1F

  3. So where’s the long winded dry supposedly intelligent response to the comments, as you promised? So far as I can see these no cap opinions cannot back up any claims they make. I’m actually starting from the no cap opinion but starting to think I’m wrong. Seems like the cap would do very little but probably even out draw on the alternator which would still help the overall system. Still very interesting to me that the no cap side seems silent on reasoning just claimes of righteousness and condescension. Hmmm.

  4. So do I need a capacitor or not? Can I just get a bigger battery n somehow add another alternator to my car? I added a capacitor n it was too much for my car n my lights still dimmed. I don’t want to hurt my car but am considering to add the capacitor back in my car since I still have everything hooked up ready to go from taking out my old one. Someone please answer me

    • U probs need to get a smaller cap and have less hooked to it. You dont even need to have a cap as big as recommended for the wattage of your amp. My reasoning is the bigger the cap the more its drawing from the battery which will not help. If u get like a .5 or 1 farad cap for like 2000watts total would be fine. I have a .5 farad cap running to a 3000watt amp and my car has a stock alt and weak battery. I used to have my subs cut out because of the lack of power avaliable but now with only adding that .5 farad did the trick and doesnt stress the battery to much

  5. I have been in the Car Audio world since the mid 80’s. I’ve worked at several custom car and home audio shops around sunny California. Back in 91′ I did an install in my friends 89′ Mitsubishi Van. 2-PPI A600’s, 1 PPI Ax400, 6-JL Audio 12W6, all MB Quart highs and mids, for a grand total of 21 speakers in the van.. hitting at 147db. Not being a retard, I did the big 3 first.

    Anyway, I remember there was an article in Car Audio Magazine about Caps… and originally Caps were never install in a system to keep your headlights from dimming. Caps were originally introduced to the Car Audio world as a way to improve the transient response of your sub woofer. Caps help your amp deliver better output when the bass hits those peaks that can cause your lights to dim.

    Plain and simple… Caps resolving your headlight and dash dimming issue is purely a side effect. Caps are for sound quality. If you want your lights to not dim when the bass hits… do the Big 3.. starting with a higher Amp output Alternator, heavier gauged wire’s, and a second battery.

    Also, find an alternator that has duel battery isolation built in. Keep your car battery for important things that the car needs to function, and the secondary battery for your entertainment system…. never allowing the audio system to draw on the car’s battery.

    One more thing that is SUPER important in wiring your car system… Separate your signal wires from your power wires. Run all your speaker wires or RCA’s on one side of the car ( usually the passenger ) and your power, ground, and trigger wires on the other. This will prevent any Alternator whine from crossing over into your signal wires.

    AND GROUND GROUND GROUND! Make sure your system is GROUNDED REALLY GOOD!.

    anyway… i’m done ranting..

    REMEMBER… if your neighbors car alarms are not going off when you drive by… you ain’t got it up loud enough.

    Have fun!

  6. A cap isn’t meant to stop your lights dimming it isn’t a cheap alternative to a lack of power but if you have a good electrical system and a large stereo particular subs they can help improve your system, ideally your amps are getting about 14.5v this supply voltage dictates how your amp work and where it will start clipping as demonstrated by some people running 16v systems now your alternator is extremely important if it can’t supply the total power needed your doomed to failure but they aren’t great at maintaining a constant voltage with large fluctuations in current draw so in heavy bass situations even with an oversized alternator you can notice clipping and flickering of your lights because the amp pulls a sudden large current and your voltage drops for a moment then your alternator ramps up to compensate then back down because the draw is gone but it is always playing catch up, your battery can help a bit but it’s only about 12.6v and a 2v drop can make a difference it’s also a chemical reaction and that has a delay as well but capacitors have very low internal resistance and can charge and discharge extremely fast so when your amp has a demand for power a cap buffers that time between when the amp calls for more power and when the alternator supplies it. A simple way to see this is to look on an oscilloscope at an AC to DC rectifier and the effect a cap has on the output

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