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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gear4wheels.com

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

  1. 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

    Reply
    • 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

      Reply
  2. 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!

    Reply
  3. 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

    Reply
  4. You got five batteries….yeah I don’t think YOU would even get stuck if your alt broke again, like ever dude, I can drive 200 miles in my 69 impala, everything off, with my one STOCK battery, lmao, you’re more than safe haha

    Reply
  5. What I would like to see is a non-biased technical article that compares car audio capacitors to real capacitors. Sure you can hop on Crutchfield and buy a 1.5F cap with fancy looking packaging and termination for $80. But skip over to Digi-Key and a 16V 1F capacitor is more along the lines of $170.

    I get the impression car audio capacitors are just big, slow, general purpose caps. I want to see if anything can be gained by using proper capacitors.

    Reply
  6. Matchpik- look up supercaps for car audio. Same theory you were asking to see.

    Pete- no, alternators are only part of the solution. For best charging, higher output or more alternators should feed into batteries. This is your best option for solid electrical with minimal drain on amp power.

    Reply
  7. I have a 100Farad capacitor bank that charges up to 84 volts.
    the premise is the same as the capacitors you all are talking about being used for your DC car audio. your battery charges the cap. only once from 0V – system voltage. when it is charged it resists amperage changes in a DC circuit. it does not really get charged over and over, it stays at balance with the voltage of your battery… your alternator supplies charge to your battery AND your cap bank. batteries having cranking amps and a cap bank having a Farad value. if your cranking amps are say 100 amps and your bass wants a bit more…. well to get those amps… it takes it from the voltage..if the voltage is stable…. IE your battery has a LARGE CAPACITY… a capacitor bank adds to the capacity of your dc system. but can discharge instantaneously whereas a battery has to MAKE the electrons move hence the cranking amps being the maximum cheeseburgers that your battery can make at a time.
    when the bass is LOUD and HEAVY.. lol you need more current to keep the voltage stable. large voltage drops affect the performance and will damage your alternator or your battery.current at lower voltages = energy loss through heat loss..and possibly thermal meltdown. .. this is the same with my set up. when I hit the throttle. I REQUIRE more amperage… rite. the voltage being supplied by the battery is somewhat stable untill i need a whole lot of amperage. like stop start and uphill….or burnouts. so, the ultra capacitor bank that i made covers that little bit more amperage that i need to cover that current draw without dropping my voltage. = more for longer without cutting out because of lowering voltage due to current draw.
    so, I hope that this helps someone understand the benefits of having a capacitor ( or many ) in your dc system..

    Reply
    • Great explanation. The difference is using ultra capacitors instead of regular capacitors. Think of an ultra capacitor as a battery super enhancer. Will be getting a 100F to improve performance and audio too.

      Reply

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