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Capacitors FAQ

What they do, and when to use one

Buck Pomerantz was born and raised in Philadelphia. His parents bought their first television set when he was born. He figured out how to run it by the time he was two. Besides athletics, his formative interests included electronics, amateur radio, music, and stage crew work. He got his BA in writing from Brown University. Then he joined a rock 'n roll band as their soundman and moved to Charlottesville, Virginia. After that venture failed, he spent time in Boston, New Orleans, and Berkeley. He worked in a music store in Austin manufacturing, installing, repairing, and operating sound systems for recording studios, clubs, and bands. He moved back to Charlottesville, ran a little recording studio and finally joined Crutchfield as a copywriter. He has 2 grown children and 3 grandchildren, but after a good nap he can still rock out.

More from Buck Pomerantz

Q: What's a capacitor?

A: A capacitor, or cap, is an electronic component that can take up, store, and discharge electrical energy. Because they can do all that quickly, capacitors are used to filter or buffer any sudden changes in a circuit's voltage, smoothing the ensuing signal.

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Q: What's a capacitor used for?

A: In car audio, large outboard capacitors, sometimes called stiffening caps, are used to prevent lights from dimming when loud bass notes play. They accomplish this by supplying the amplifier with a quick jolt of power.

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Q: Even if my lights don't dim, won't a cap still improve my system's low end response and overall sound?

A: Not really. A cap prevents the sound from deteriorating due to under-voltage, but doesn't actually improve the sound. It supports the amplifier by feeding it the power it needs for short bursts. So, while not improving sound quality directly, a cap does make it easier for the amp to perform its best.

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Q: What size cap should I get?

A: The rule of thumb is to put in 1 Farad of capacitance for every 1,000 watts RMS of total system power. But there is no electronic penalty for using larger value caps, and in fact, many see benefits with 2 or 3 Farads per 1,000 watts RMS. The larger the cap, the faster it gets ready for the amp's next big hit.

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Get Everything You Need

Give your subwoofer amp the boost it needs with a capacitor. We also have all the installation hardware you need to get your capacitor and amplifier up and running.

Q: How do I hook up a capacitor?

A: If you don't have the instructions that came with your capacitor, you should know first off that a cap can be dangerous; it can charge and discharge so much power so very quickly that it can weld metal objects, like tools and jewelry, and melt its own insides out. A new cap comes completely discharged, so it's safe. A resistor or wired light bulb usually is included in the package. Wiring the bulb or resister across the cap's terminals allows the capacitor to discharge slowly and safely. The same bulb or resistor, wired differently, also gets used to charge up the cap safely.

As in all car electronic installations, start by disconnecting the ground cable from the car battery. In this installation, also take out the in-line fuse on the amp's power wire next to the battery.

A capacitor should be mounted as close to the sub amp as possible using the shortest wires possible. This is so the extra charge doesn't have far to go to get to the amp quickly. Make sure the cap gets mounted securely and won't become a dangerous flying object in the event of an accident.

A capacitor has two poles: a positive and a negative. They should be clearly marked on the capacitor. The positive connects to the same positive power lead that goes to your sub amp's positive, 12 volt, connection. Use the same gauge wire as the amp uses for its power. This can be accomplished with a distribution block. Or, sometimes, the cap comes with multiple connection terminals that make it easier to wire it into your system. The multiple terminals act just like a distribution block so, for instance, the power wire coming from your battery can connect directly to the cap's positive terminal while a short cable connects from there to the amp's positive power connection. The negative pole of the capacitor connects to your chassis ground, just like the amp. The best practice is to use the same bolt the amp uses for ground. Make sure all the paint is scraped off around where you put the chassis ground and the connections are clean and tight.

Next, you need to charge up your capacitor. If done too quickly — it could "pop," destroy the cap.

If you don't have the original charging/discharging resistor or light, you'll need to get one. An automotive 12-volt test light, the kind with a bulb, not a small LED, will do nicely. Otherwise, you can use a high-wattage, low resistance resistor, available at most electronics parts stores. The exact value doesn't matter, but get one with a value of 10-1,000 ohms along with a rating of 1-20 watts. The lower the resistance, the higher the wattage should be.

Take the test light or resistor and connect it to the two terminals of the amp's in-line fuse holder (where you took the fuse out earlier). Re-connect the car battery's ground cable. The resistor will get hot, or the bulb will light up, while the cap charges. After 10 to 30 minutes, the bulb will fade out, or the resistor will start to cool. Remove the light or resistor carefully — they can get very hot. As you replace the fuse, you may experience a small spark — that's okay, but should remind you of how powerful the electric forces involved are. Your capacitor is now installed.

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Q: My cap has a third terminal. What's that for?

A: Some caps come with a built-in meter that displays the voltage. If a meter were to stay on constantly, it could drain the car's battery. So caps with meters often have a remote turn-on lead connection, just like car amplifiers, so the meter turns off with the system. A thin, 18-ga. or so, wire should run from the cap's turn-on connection to the amplifier's remote turn-on terminal, or any other switched 12 volt power source.

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T-Spec capacitor

T-Spec 3.0-farad capacitor

  • K. Hardy from Calgary, Alberta

    Posted on 4/25/2015 5:15:59 PM

    Can capacitors be mounted on the firewall under the hood?

  • K. Hardy from Calgary, Alberta

    Posted on 4/25/2015 5:30:26 PM

    Does a powered subwoofer also need a capacitor connection?

  • Buck Pomerantz from Crutchfield

    Posted on 4/27/2015 10:01:07 AM

    K, A capacitor can certainly be used with a powered subwoofer. A capacitor should always get mounted as close to the subwoofer's amplifier as possible, never under the hood in the engine compartment.

  • John from New york

    Posted on 4/27/2015 7:43:07 PM

    Can you put one cap on two amplifiers ?

  • Buck Pomerantz from Crutchfield

    Posted on 4/28/2015 10:26:21 AM

    John, A capacitor gets wired with one wire running from its negative terminal to ground and one wire from its positive terminal to the positive 12-volt power line of an amplified system. It does the most good to connect a cap closest to the subwoofer amplifier in a system, but it won't hurt to connect it elsewhere, like at a distribution block.

  • Cory Dzbinski from Oceanside, CA

    Posted on 5/14/2015 2:50:08 AM

    Hey there, good article. I have a question that seems obvious to me but I haven't see it asked or explained anywhere. Won't the cap slowly discharge when it's off? What if you don't drive your car for a couple weeks. Won't the cap be empty and be at risk to "pop" and destroy the cap if it then recharges quickly?

  • Buck Pomerantz from Crutchfield

    Posted on 5/14/2015 9:56:27 AM

    Cory, As long as the vehicle's battery maintains a charge, it will keep the cap charged. If the battery loses its charge or gets disconnected, then the capacitor will lose its charge and need to be re-charged slowly, like it was newly installed.

  • Lee

    Posted on 7/12/2015 9:11:21 PM

    I have had great success with stiffening caps in-line with A/B amps. Will a cap help with a class G amp?

  • Buck Pomerantz from Crutchfield

    Posted on 7/13/2015 4:03:11 PM

    Lee, A capacitor's function is unaffected by the technological Class of an amplifier's internal circuitry.

  • Nick Duval from Canada

    Posted on 7/18/2015 1:14:11 AM

    My capacitor has recently starting making a high pitched screeching noise what could cause this? It doesn't happen all the time, it happens randomly.

  • Buck Pomerantz from Crutchfield

    Posted on 7/20/2015 8:50:02 AM

    Nick, I have never personally heard of such a thing, but it probably is not good. I have seen capacitors fail by springing a leak, developing a hole where internal gases have pushed through the casing. Maybe that's what's happening to your cap.

  • Amanda

    Posted on 7/25/2015 9:58:24 AM

    Hi! I just want to ask if an audio capacitor has fumes? And if it has fumes in it, can it be dangerous to our health? Is there any chance that the fumes will leak? Hope you could reply to my email asap. Thank you!

  • Buck Pomerantz from Crutchfield

    Posted on 7/25/2015 4:52:09 PM

    Amanda, There are no fumes or gas inside capacitors. Capacitors are made of two foil sheets wrapped together with a chemical called a dialectic in between them. Like in a car battery, this substance may contain some acid, but you'd have to rub it in your eyes, roll in it, or eat a bunch before it would do you any harm. That being said, I think it is possible that when a capacitor fails catastrophically the electric charge could vaporize some of the dialectric and release a small puff of gas that if breathed in probably won't be good for you. If you or a friend think you've been exposed to such a thing, I recommend flushing the area out with water, and contacting your doctor for advice.

  • sr5573 from bhubaneswar

    Posted on 7/30/2015 2:13:10 PM

    what is the working principle of a capacitor?

  • Buck Pomerantz from Crutchfield

    Posted on 7/30/2015 4:01:38 PM

    SR, Check out this 5-page article How Capacitors Work. It ought to answer a lot of your questions about capacitors.

  • pelonomi from gaborine

    Posted on 8/4/2015 2:53:05 AM

    hi, amplifier(1200W), subwoofer(1000W), 6x9 speaker (350W), twitter(300W) and capacitor connected between amp and power source, my question is there is disturbing noise when car rev or on drive what could be the cause of that, and most of the time fuse (connecting amp with power source) are blown

  • Buck Pomerantz from Crutchfield

    Posted on 8/4/2015 12:08:25 PM

    Pelonomi, The number one cause of engine noise in a car audio system is a loose or intermittent ground connection. That could also explain the blowing fuses. Carefully check your amplifier's power and ground wiring and correct any faults you may find. Make sure the ground wire makes a clean, tight, and paint-free contact with your vehicle's chassis.

  • Mike from Santa Rosa Beach, FL

    Posted on 8/5/2015 1:48:29 PM

    How do you determine the MAX AMP INPUT/CHARGING AMPS a Capacitor can handle??? I would LIKE to connect a capacitor directly to the ALT. Output(My Stock one is 130AMP), to isolate the sub-woofer and any other amplifier circuit I add in the future. I have found that the MAXWELL Super-caps (2.7VOLT 350-500F), with 6 of them bundled together, 16.2VOLTS and 3000F, would make a great substitute for the car battery, as long as they don't drop below 10-11VOLTS or go without being charged for more than 2 days... What worries me, will the 130AMPS coming from my ALT destroy the caps??? THANK YOU SO MUCH in Advance!!!

  • Buck Pomerantz from Crutchfield

    Posted on 8/6/2015 10:23:00 AM

    Mike, The capacitors made for car audio application are all made to handle the high current that flows when the cap charges and discharges. You'll have to find out the current-carrying capacity of your super caps from the manufacturer.

  • Justin Stefko from Newton

    Posted on 8/6/2015 12:03:25 PM

    Can power capacitor be rebuilt or repaired? I have a 30 figured that doesn't work

  • Buck Pomerantz from Crutchfield

    Posted on 8/6/2015 4:48:51 PM

    Justin, I'm afraid not. Capacitors are replaceable, but not repairable.

  • Kel from Nashville

    Posted on 9/17/2015 1:55:57 PM

    I am about to change vehicles, and was wondering if I should replace my capacitor. I have used the capacitor for a little over 3 years and didn't know if replacing it was necessary?

  • Buck Pomerantz from Crutchfield

    Posted on 9/17/2015 2:11:55 PM

    Kel, It is not absolutely necessary to replace your capacitor, but it may help if your car's headlights dim a little when your music plays loud.

  • Kiran

    Posted on 10/7/2015 7:31:33 PM

    My battery capacitor isn't charging fast it take at least 8 hours and is only half charged,, is there a reason for this?

  • Buck Pomerantz from Crutchfield

    Posted on 10/8/2015 10:18:48 AM

    Kiran, It sounds like your capacitor has failed - it's probably leaking its charge internally.

  • Trey from Uvalde

    Posted on 11/5/2015 2:40:20 AM

    It may sound stupid but, can you connect your capacitor to the same ground area as your amplifier?

  • Buck Pomerantz from Crutchfield

    Posted on 11/5/2015 11:55:24 AM

    Trey, The ground point used by your amplifier is a great place to also ground your capacitor.

  • Jason Flanigan from LEXINGTON

    Posted on 11/15/2015 3:50:33 PM

    Is a 20 Farad Capacitor on a 1500watt amp to big

  • Buck Pomerantz from Crutchfield

    Posted on 11/15/2015 5:21:58 PM

    Jason, Like this article states, there is no electronic penalty for using large value caps - the larger the cap, the faster it gets ready for the amp's next big hit

  • joe from Cincinnati

    Posted on 11/16/2015 2:54:29 PM

    Hi. I have a 300W powered 10" sub Rockford Fosgate. My lights do not dim, etc. I bought 1.5 farat capacitor, but do I even need it, or will it provide any benefit? It's installed in a 2015 car that has a bunch of electronics, etc, and i didn't want my amp to kill my alternator faster, or worse, cause an electrical problem by pulling directly from the battery, instead of using a capacitor. Am I being paranoid? Is the capacitor beneficial in my case?

  • Buck Pomerantz from Crutchfield

    Posted on 11/16/2015 3:34:43 PM

    Joe, I would think that a 300 watts RMS amp added to a car's stock electrical system would not need a capacitor, but wouldn't be harmed by one either. The only way to know for sure is to remove the capacitor and see if your lights dim on heavy bass hits. If they do, re-install the cap. If they don't dim, then you never needed it to begin with.

  • Matt from Indianapolis

    Posted on 11/23/2015 5:16:50 PM

    I have a cap with a meter and it does not have a remote turn-on connection. Do I need to be worried about this draining my battery?

  • Buck Pomerantz from Crutchfield

    Posted on 11/24/2015 1:03:06 PM

    Matt, I think the current draw of your capacitor's meter is as small as your vehicle's clock and won't drain a healthy battery when left unused for a while. If the battery is weak or needs replacing, however, that small draw may be enough to leave you powerless.

  • Bret Weaver from Clinton

    Posted on 11/28/2015 3:32:53 AM

    How do I wire up 2 amp' s to a capacitor?

  • Buck Pomerantz from Crutchfield

    Posted on 11/30/2015 2:35:36 PM

    Bret, Here's a diagram that shows how a capacitor hooks up in a typical 2-amp system.

  • Todd from Lexington

    Posted on 12/9/2015 10:04:17 PM

    I noticed the mention of using same size wire for amp and capacitor. I used 8 gauge from battery to cap and 4 gauge for the small cap to amp wire. Should I make it all 4 gauge?

  • Buck Pomerantz from Crutchfield

    Posted on 12/10/2015 9:57:12 AM

    Todd, The size power and ground wires to use in a system is dependent solely on the total power requirements (current draw) of the amplifiers. If you're using one amplifier and it requires 8-gauge power and ground wiring (see the owner's manual for that specification), then 8-gauge will do for the capacitor, although using a larger wire won't hurt anything.

  • Chris from Brunswick

    Posted on 12/21/2015 11:56:05 PM

    I noticed on my capacitor there is a third spot for a remote wire. So with the remote turn on coming from the radio to the amp like i normally have it, should i run the remote wire from the radio to the capacitor, then jump it from the capacitor to the amp? I dont understand how to hook up the remote turn on. Ive been trying to find out how and i can't find any answers!!

  • Buck Pomerantz from Crutchfield

    Posted on 12/22/2015 12:02:47 PM

    Chris, If your capacitor uses a remote turn-on, for an onboard meter for instance, it doesn't matter if it gets the connection directly from the receiver and then daisy-chain it on to the amp, or the other way around. Most people just run a jumper from the amp's remote connection to the cap's.

  • Chris from Brunswick

    Posted on 12/22/2015 4:44:56 PM

    Thanks for your response. So if i jump a seperate wire from the remote terminal from the amp to the third terminal on the capacitor it wont hurt anything will it?

  • Buck Pomerantz from Crutchfield

    Posted on 12/23/2015 12:19:30 PM

    Chris, No, it won't hurt anything - that's how you hook it up. It sounds like you don't have the instructions that originally came with your capacitor. You should know that a capacitor can be dangerous; it can charge and discharge so much power so very quickly that it can weld metal objects, like tools and jewelry, and melt its own insides out. Please follow the steps in this article, or from another reputable source, telling how to hook up a capacitor safely.

  • yannick from mauritius

    Posted on 12/28/2015 10:44:52 AM

    hi, note that i have a pioneer champion series amplifier powering a JBL subwoofer of 300 watt and 4 speakers of 80 to 100 watt for the high. when i play music for some time at higher volume and the bass are kicking hard, after a certain period of time, the music stops for 1 to 2 seconds and continue to play again. i therefore need to play the music below level 10 (30 to be the highest) so that the periodic "1 second cuts" stop. do you think that it's the power consumption and that i will need a capacitor to resolve this issue or it is being caused by another issue? Thanks

  • Buck Pomerantz from Crutchfield

    Posted on 12/28/2015 4:03:17 PM

    Yannick, Here are some things to check for: Are you using 4-gauge power and ground cables for your amp? Are there any loose connections? Is the ground wire absolutely secure - bare metal-to-bare metal contact? If you bought your amp from Crutchfield, you could call Tech Support for free help troubleshooting your system. Their toll-free number is on your invoice. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support - 90 days-worth for only $30. Click on this link for details.

  • Buck Pomerantz from Crutchfield

    Posted on 12/29/2015 12:51:21 PM

    Yannick, Sorry, I just now figured out that you don't live in the U.S. and so can't buy Crutchfield Tech Support. Your problem, 1 to 2 second cut-out every once in a while, sounds more like a loose connection or defective amplifier than anything else. I suggest you take your vehicle back to the installers and have them diagnose and fix the issue.

  • Ryan from Fort Wayne

    Posted on 1/7/2016 2:53:21 PM

    I recently purchased a new capacitor. While unwrapping it I cut through the clear plastic wrap or heat shrink around the cap. It had the brand name on it. Is the wrap needed or can I peel it off and just have the bare aluminum. I wasn't sure if the wrap was an insulator or just for appearance. Thanks!

  • Buck Pomerantz from Crutchfield

    Posted on 1/8/2016 3:25:33 PM

    Ryan, Maybe the wrapper serves as an electrical insulator, maybe not. The only way to find out for sure is to check with the manufacturer.

  • Chris

    Posted on 2/3/2016 4:55:31 PM

    If i am running 2100 rms amp with 2 1000 rms subs , what kind of capacitor do i need? I am guessing 3 farads?? And also a 600 rms amp inside for highs ... Also planning to put a battery in trunk as well

  • Buck Pomerantz from Crutchfield

    Posted on 2/4/2016 3:37:49 PM

    Chris, Like the article says, the rule of thumb is to put in 1 Farad of capacitance for every 1,000 watts RMS of total system power, but there is no electronic penalty for using a larger value cap. A 3 Farad cap will be fine for your system to help prevent light-dimming when your music hits hard.

  • Edgar from Fontana

    Posted on 2/8/2016 4:48:15 PM

    Hi I'm having a problem with my battery drained and my compacitor staying on my compacirtor has a meter on it and I already plugged in the remote but the capacitor still stays on what's the problem?

  • Buck Pomerantz from Crutchfield

    Posted on 2/9/2016 11:41:53 AM

    Edgar, Capacitors, in car audio applications, are passive electronic devices connected to constant 12-volt power and ground, so they are always on. If you are referring to a voltmeter display, the remote lead is supposed to connect to switched 12-volt power that turns off when the car is off. You may have to find a different spot to connect your remote lead. Some capacitors have displays that sense when power flow stops and turn themselves off after a few minutes.

  • Dallas

    Posted on 2/10/2016 9:35:37 PM

    Hi, i have a BOSS CAP8 capacitor and i was wondering if it was okay to just use the capacitor as a positive distribution block?

  • Buck Pomerantz from Crutchfield

    Posted on 2/12/2016 10:42:42 AM

    Dallas, It probably won't hurt anything installing your capacitor's positive terminal to the main power cable and a couple amplifier positive leads, if the main power cable can handle both amps. But it will do the most good connected to the subwoofer amp's positive lead only and as close to that amp as possible.

  • Travis from Hope mills, NC

    Posted on 3/2/2016 12:27:16 PM

    Have 2 questions I have two 12" subs at 1200w with a 1200w amp 1.5f capacitor I plan on adding a 400w amp to power two tweeters 1) will this be too much power for my cap and have negative effects? Or is the power draw from the tweeters manageable without increasing the cap size 2) might sound lazy but is it possible to wire that second amp through the capacitor, using it as a distribution block, and if so does the same gauge wire need to be used as the 1200w amp

  • Buck Pomerantz from Crutchfield

    Posted on 3/2/2016 3:39:07 PM

    Travis, Not knowing exactly what amplifiers, tweeters, subs, or capacitor you have makes it impossible to give advice on how it all could get wired together. 400 watts seems like a huge amount of power for a set of tweeters, but that may be a peak spec and you'll be okay. And using a cap for a distribution block is a bad idea - how do you know that the main power wire from the cap's positive terminal to the battery can accommodate both amps? Capacitors are really only effective providing jolts of power for a subwoofer amplifier anyway.

  • Brett from Newtown, PA

    Posted on 3/3/2016 9:46:22 PM

    Hi I'm finishing up the install of my car audio system this weekend and have a question. My car is a 1965 Mustang and I'm using a 1.5f capacitor with a 1500 watt 5 channel amp. Before big audio system, I regularly take the battery terminals off and put the battery on a tender to keep it "fresh" since I don't drive the car very often. I assume then since I remove the battery supply, the cap will discharge as from what I'm reading about now with capacitors (sorry I'm all new to car audio world). Is there anything you'd recommend in my case then? Do you know could I leave the terminals bolted/quick clipped on the battery and pop the Tender's clips right on there to keep the battery charged up, through the down times? Thank you much!

  • Buck Pomerantz from Crutchfield

    Posted on 3/4/2016 4:37:19 PM

    Brett, You can definitely leave your battery hooked up in your Mustang while you keep the battery charged with a battery tender.

  • Jeremy from Grande prairie

    Posted on 3/8/2016 6:04:41 PM

    I'm installing a 300w rms amp/300w rms subwoofer in my Toyota Echo. I have a 90amp alternator and a 30-40 ah battery. The vehicle isn't fully loaded so it has manual roll up windows no a/c etc... (Also I bought an Aftermarket pioneer stereo) anyways the question is do i need this 2 farad capacitor or will it just harm my battery or alternator and provide no real benefit. I don't know if my lights will dim I haven't installed the sub/ amp yet

  • Buck Pomerantz from Crutchfield

    Posted on 3/10/2016 9:26:38 AM

    Jeremy, I don't think that amplifier will be too much for your car's electrical system to support, so you probably won't need a capacitor at all. Even if you installed one anyway, it would not harm your alternator or battery.

  • Juan from Minneapolis

    Posted on 3/15/2016 12:48:31 AM

    I have mine wired the 12v output of the cap(10 farad) to a DST then from there to feed my two amps one is a 4 channel and the other one is a monoblock Im a wasting power by doing this? is it better to just run the monoblock from the cap? also I also read that all the grounds should be at the same point if possible, I have my mono block ground attached to my Cap because it has two Ground terminals. Is this wrong?

  • Buck Pomerantz from Crutchfield

    Posted on 3/16/2016 4:30:47 PM

    Juan, It is best to mount and connect a capacitor by the subwoofer amplifier because that's where it does the most good, but I don't think it'll hurt anything installing it elsewhere on the power line. The rule of thumb for audio installations is to have all the gear grounded at the same point, but if you aren't getting any noise or interference with the way you have your grounds, go ahead and leave them as they are.

  • randy brillon from spokane

    Posted on 3/16/2016 4:54:16 PM

    im having an issue with my Capacitor i got for my stereo it seems to want to stay charged up even when im not bassing out and the last couple days its ran my bat dead by i assume its trying to stay charged up all night draining my bat what i want to know is it ok to put a power cut off to cut the power from the m,ain bat to the capacitor? like an inline toggle switch between the power distribution block and the capacitor? will it hurt the capacitor to have power cut off from it all the time ?

  • Buck Pomerantz from Crutchfield

    Posted on 3/17/2016 9:39:25 AM

    Randy, A capacitor is supposed to stay charged when hooked up. Like the battery it's connected to, it's supposed to just sit energized without draining the charge when no current is flowing. Try disconnecting the capacitor and see if that was the reason your battery drained. Maybe something besides a defective cap is the culprit. And do not put a switch in-line with your capacitor. Turning on and turning off the current flow suddenly to a capacitor will most likely damage it.

  • Jason from Fort Worth

    Posted on 5/23/2016 1:27:24 AM

    Buck question for yea. How do you know if a cap has gone bad in your system? Had the cap for 3 years with no probs. No leak in the cap. Has electronic display, display does Not stay on after charged. Uses a resistor to charge cap up however drains the battery after charged? 500k microfarad Scosche capacitor running on a 700 watt 4 channel amp with 50 amp fuse. Replaced the battery, charged the cap back up, drained the battery quick again. Removed the cap, hooked the amp up direct, car started right up. My thought is the current is back feeding causing a short in the battery?

  • Buck Pomerantz from Crutchfield

    Posted on 5/23/2016 12:54:59 PM

    Jason, If your battery drains when your capacitor is in the circuit, but does not when the cap is not in the circuit, then I'd leave the cap out. It sounds like it's developed an internal short. Usually, an electrical system won't need a capacitor to handle an amplifier capable of pulling 50A.

  • Norman DeRemer from allentown

    Posted on 6/3/2016 7:17:52 AM

    I just installed my new capacitor and the voltage meter stayed on all night. It was reading 12.4 volts the next morning. My amp and cap are grounded at the same spot, is that ok? And the voltage meter, will that being on all night eventually kill my battery? I use my truck almost every day.

  • Buck Pomerantz from Crutchfield

    Posted on 6/3/2016 12:04:12 PM

    Norman, A tech with T-Spec told me that the volt meter on their capacitors can sense current flow and turn on when the engine is on, and slowly turns off when the engine's off. Maybe your capacitor works differently. I wouldn't think any reputable capacitor manufacturer would put out a product that would drain and possibly damage a car battery.

  • Joey

    Posted on 6/5/2016 9:23:43 AM

    Hey I got a 3.5 farad cap and it was for my one 15" sub atm I'm only using a 1,400 watt amp, I want to upgrade my system with 2, 4k watt 15" subs/amp and 2 8" subs with a 600-800 watt amp. Can I get another cap at like 4 or 6 farads and put them in a series or should I just outright buy a bigger one?

  • Buck Pomerantz from Crutchfield

    Posted on 6/6/2016 3:29:52 PM

    Joey, I suspect those astronomical power ratings you mention are peak amplifier ratings, which should not be used when planning systems. The rule of thumb for capacitors is to have 1 Farad of capacitance for every 1000 watts RMS of amp power. Your 3.5 Farad cap can handle a 3,500 watts RMS system. If yours is indeed larger, then get a new larger cap, if you need one at all.

  • scott

    Posted on 7/1/2016 4:05:37 PM

    i got 2 12" subs and a 2400w mono amp and was wondering how big of a cap would be recommended for it to perform properly and not drain my battery dead also was wondering what a cap brand makes a really high quality cap thats gonna be reliable and has a good capacity

  • Buck Pomerantz from Crutchfield

    Posted on 7/3/2016 10:41:48 AM

    Scott, Like the article says, the rule of thumb is to put in 1 Farad of capacitance for every 1,000 watts RMS of total system power. But there is no electronic penalty for using larger value caps, and in fact, many see benefits with 2 or 3 Farads per 1,000 watts RMS. The larger the cap, the faster it gets ready for the amp's next big hit. For you, if your amp truly is 2400 watts RMS and that wasn't a peak number you quoted, a 3.0 Farad T-Spec capacitor will work well.

  • Dan from Austin

    Posted on 7/8/2016 8:05:00 PM

    Hi, I have an RF 1 F capacitor off the battery that splits the power line to an Infiniti Basslink powered sub and an RF 4 channel amp that feeds 4 speakers. I get a lot of alternator whine and noise in the audio. I've checked all the grounds and they all look good (short runs, solid contact to chassis, paint sanded off). I had the polyfuse in the Pioneer HU replaced because I had hot-swapped the RCA cables in the past, and the RCA cables are all new. Could the cap be a cause of the signal noise?

  • Buck Pomerantz from Crutchfield

    Posted on 7/11/2016 9:06:56 AM

    Dan, Alternator whine or engine noise is indicative of a bad ground, or a defective head unit or amplifier, or a radiating electrical system, and usually has nothing to do with a capacitor. If you bought your gear from Crutchfield, you could call Tech Support for free help troubleshooting your system. Their toll-free number would be on your invoice. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support - 90 days-worth for only $30. Click on this link for details.

  • Thomas Murphy from Lonoke

    Posted on 7/12/2016 11:21:21 AM

    What if your cap does not have a remote terminal, but still comes on when fuse is hooked up as apposed to when ignition is turned on and powered up like the amp does? The amp comes on when the key is turned on, but the cap is acting like it has a constant power and turns on as soon as I install the inline fuse...

  • Anthony Dragani from Swampscott

    Posted on 7/12/2016 12:02:59 PM

    Hey I could use some guidance. I have a sailboat with an autopilot that is effectively an inductive load (DC motor pulses on and motor turns clockwise or counterclockwise to steer boat on course). The problem is I can see the voltage drop when the motor pulses on. My instruments don't like the resulting voltage drop. I think a cap would compensate for the inductive load and provide the current spike without drawing the voltage down. I would like to have the cap discharge when I leave my boat for safety reasons. So I would to charge it when I turn instruments on. I am trying to find out the motor spec. s to find out how much instant current it needs for each pulse. I think I may be looking at an amp at 12 volts but that is WAG. What would work for me size cap with charging and discharging included? Or what do I need to look for in picking one?

  • Buck Pomerantz from Crutchfield

    Posted on 7/12/2016 3:49:21 PM

    Thomas, A capacitor is supposed to be "on" and fully charged up at all times, whether the amp or car is on or not. After all, if it's installed correctly, it connects to a constantly-powered 12-volt power line and ground. The remote lead on some caps is to turn the volt-meter or some other feature on and off, not the cap itself.

  • Buck Pomerantz from Crutchfield

    Posted on 7/12/2016 3:50:43 PM

    Anthony, I'm not at all sure that a capacitor suitable for smoothing out voltage fluctuations due to an audio amplifier's power usage will work the same way for the autopilot motors in your boat. I guess in theory it could work, but without any idea of the duty cycle or current draw of the system make figuring out the proper cap size virtually impossible. I suggest you contact the manufacturer of your boat or autopilot and ask their tech department if a capacitor would work in your situation, and if so how big should it be.

  • S

    Posted on 8/7/2016 11:06:32 PM

    dialectic??? (7/25/2015) Might want to look up the definition of "dialectic" then look up "dielectric."

  • Buck Pomerantz from Crutchfield

    Posted on 8/8/2016 9:42:14 AM

    S, You got me on a misspelling. Thanks for the catch.

  • christian quiroz from riyadh

    Posted on 8/21/2016 12:43:52 AM

    i have a question? when i put a capacitor wired direct to battery (+ to +) then ground, my question is, how about when you the car is off, the capacitor is still on? or also automatically off when you off the car? thanks

  • Buck Pomerantz from Crutchfield

    Posted on 8/22/2016 9:57:29 AM

    Christian, Even when your car is "off," the battery will keep the capacitor charged. The cap is, I guess, technically "on," it has a charge, but it isn't doing any work (passing current while discharging and recharging). In effect, the capacitor is an extension of the battery itself, charged and ready for work when the switch is thrown.

  • Brian from Idaho

    Posted on 9/6/2016 3:56:18 PM

    I've studied Crutchfield's amplifier (and cap) installation diagram, available at I see the cap + is connected to a + distribution block which provides + to two amps. By using a distribution block this way doesn't the cap actually provide support for both amplifiers, equally? I have three amps all tied into a single + dist block. If I were to add a cap via that + dist block, would all three amps get cap support (and I should size my cap accordingly, correct?).

  • Buck Pomerantz from Crutchfield

    Posted on 9/6/2016 4:16:27 PM

    Brian, You're right, a capacitor electrically connects to all parts of the positive power wiring. It's restorative effects, however, are best felt by the amplifier that's closest to it.

  • edward coolz from daphne

    Posted on 9/7/2016 1:42:03 PM

    hey buck i have 3 1ohm powerbass 12s running a 1000 watt audiopipe to them they sound very good and im more than impressed with the bass im getting.. my question is what are some pointers on how should my amp settings should be i have the hardest time getting my amp tuned just write what are some simple steps or do u kno the readings i can set them amp..

  • Buck Pomerantz from Crutchfield

    Posted on 9/7/2016 2:08:59 PM

    Edward, Check out this how-to article for help tuning your subs.

  • Now hear this

    Posted on 9/17/2016 12:16:34 PM

    I have a 800 RMS subwoofer amp installed in a recreational vehicle. I have a dual battery setup where there is the standard starting battery and then I put in a big marine deep cycle battery to run the amplifiers. The battery cable runs to the amps are quite long in comparison to a car. I have 2 gauge cables though that seem to be doing fine. I noticed that the sub bass was not quite as clear and crisp as I thought it should be so I bought a 18 farad capacitor and installed it right at the subwoofer amp. Immediately noticed that the punch of the sub bass was much tighter and cleaner. My only problem now is that we only occasionally use this vehicle and I've blown out the capacitor a couple times which I think is occurring because it is discharging completely over time and when I turn the battery switches on it is probably causing too much current flow. I had to put in the battery switches because otherwise both batteries would always be dead when we went to use it. The battery switches stopped that problem. Is there a way other than disconnecting the capacitor each time and using that little resistor to charge it that the capacitor can be protected from these initial current spikes that seem to be killing it? A relay? A choke?

  • Buck Pomerantz from Crutchfield

    Posted on 9/19/2016 9:31:39 AM

    Now, A capacitor should stay charged to the same voltage as the battery it's connected to. If your cap loses its charge while the batteries maintain theirs, the cap is defective. Or, it isn't connected correctly: between constant 12 volt positive and ground.

  • Now hear this

    Posted on 9/19/2016 4:29:50 PM

    Buck, if I may follow up to my first question, the cap is not losing its charge while the batteries are connected. It's losing its charge because as you know there are parasitic things that steal current all the time. My head unit is one of them. Even when it is off it is stealing a tiny bit of current (probably to maintain some settings). This is what discharges the capacitor eventually when we don't drive the thing for a while. And I know this happens to other guys who have some toys they don't drive that often. What the capacitor manufacturers should do is put in an input current limiter for when the voltage is real low then allow full current flow once the voltage goes beyond 8-9 volts. That would protect the capacitor no matter what anybody did with it.

  • Buck Pomerantz from Crutchfield

    Posted on 9/19/2016 4:50:08 PM

    Now, A capacitor needs to be always connected between constant 12 volt positive and ground, not a switched source of power. As soon as the battery gets disconnected, the cap will start to drain. Instead of wishing that a cap manufacturer will accommodate your misuse of their product, you should find out the source of your parasitic drain and fix that, or use a battery charger to maintain the system's charge when in storage. Otherwise you're stuck using that resister to slowly recharge your cap every time you switch the batteries on, or risk damaging it.

  • D from nevada

    Posted on 9/26/2016 8:42:04 PM

    can a cap be used other than car stereo equipment ? such as cb radio amps ?

  • Buck Pomerantz from Crutchfield

    Posted on 9/27/2016 11:11:56 AM

    D, Capacitors can work in many different applications to smooth power supply fluctuations or to filter out certain frequencies in a signal's flow. In car audio, a cap usually is called for in systems of over 750 watts RMS output power. If you think your CB radio amplifier is drawing too much power from your vehicle's electrical system, you can connect a cap between its positive power wire and ground just like it was an audio amp to ensure smooth 12-volt power flow.

  • Justin

    Posted on 10/18/2016 11:15:53 AM

    Can or should one be used with an amp that's only going to drive speakers and not subs?

  • Buck Pomerantz from Crutchfield

    Posted on 10/18/2016 3:13:47 PM

    Justin, In the event of light-dimming when the music hits in a system, even one without a sub amp, a capacitor can often help maintain smooth power flow for an amp's power supply.

  • Neil from South

    Posted on 11/3/2016 12:00:12 AM

    Hey, Please can you tell me the formula for calculating the RMS of total system power? Thanks

  • Buck Pomerantz from Crutchfield

    Posted on 11/3/2016 11:06:47 AM

    Neil, The total RMS wattage of a system is simply the sum of the RMS wattages of all the channels. For example, the total power of a system consisting of a 50 watts RMS per channel 4-channel amp for speakers plus a 500 watts RMS sub amp is 700 watts RMS. (50 x 4) + 500 = 700.

  • Matt from Burrillville

    Posted on 11/22/2016 1:13:22 PM

    I've got a capacitor hooked up between my battery w/ fuse and a chassis ground, it's supplying power to my amp. It has worked for years with this setup, but recently my car's battery connector came loose and a few days prior to being able to tighten it with a wrench I was just jiggling it by hand to make the connection and get the car started. Still getting around 14.5V measured at the battery terminals, but my cap no longer charges to the battery's voltage. It peaks around 9V and shuts off. The toyota battery connectors are old and need to be replaced anyway, but could an inconsistent battery connection have ruined the cap?

  • Buck Pomerantz from Crutchfield

    Posted on 11/22/2016 1:51:38 PM

    Matt, An intermittent power connection, one that turns on and off a lot, can definitely contribute to a capacitor's destruction.

  • Rixon from Abudhabi

    Posted on 12/15/2016 5:59:50 PM

    I have JBL ms15sd2,1800watts 450watts RMS.2 ohms .and Alpine MRV M 500 amp so which will be suitable capacitor for my system...?

  • Buck Pomerantz from Crutchfield

    Posted on 12/16/2016 10:41:12 AM

    Rixon, Like the article states, the rule of thumb is to put in 1 Farad of capacitance for every 1,000 watts RMS of total system power, but there is no electronic penalty for using larger value caps. In your case, with a less-than 1,000 watts RMS of amplifier power, a 1- or 1.5-Farad capacitor will do.

  • Slu from lusikisiki

    Posted on 12/30/2016 7:26:56 AM

    The capacitor can help to automatically stop the music when the battery becomes low ?

  • Buck Pomerantz from Crutchfield

    Posted on 12/30/2016 9:58:59 AM

    Slu, Not really. A cap prevents the sound from deteriorating due to under-voltage, but doesn't actually improve the sound or energize the battery. It supports the amplifier by feeding it the power it needs for short bursts.

  • David from England

    Posted on 1/18/2017 7:58:09 PM

    Hi, I'm using a 1 Farad cap in a portable 12v sound system, which can run on a 12v battery or a computer power supply unit. So when not in use the psu or battery is disconnected from the system. On the two amps I'm using a jumper between remote and pos to turn them on when I hook up the power source. I have two questions, firstly will the cap act as battery and provide power to turn on the amps (and drain the cap) when the power source is totally removed? And secondly, when I remove the power source will the cap drain and is this bad? I appreciate any help, thanks

  • Buck Pomerantz from Crutchfield

    Posted on 1/19/2017 10:52:17 AM

    David, Capacitors are usually used in 12-volt applications to provide a quick jolt of energy to a subwoofer amplifier so a vehicle's charging system, the alternator, can catch up with a voltage drain due to the amp's current demand. Think of one like a spring that provides a lift, but then needs to get squeezed back together again for re-charging. If a capacitor has its power removed and is still connected to an amp (in circuit), it will slowly discharge. Whether that would be enough to actually turn the amp on for a little while - I don't know. Charging and discharging caps quickly is what kills them. I really don't see any benefit in using a capacitor in the manner you describe.

  • David from England

    Posted on 1/19/2017 11:08:50 AM

    Thanks a lot Buck, much appreciated. I've removed the cap from the system now!

  • Dan from Canada from Brandon

    Posted on 1/21/2017 5:18:45 AM

    Hi Buck I was charging my 1 farad capacitor with a resistor. The led display and my multimeter were showimg different voltages while charging. Then at 12V charge and nothing hooked up but the test leads, meter was showing voltage drop 4-5 volts in one minute. Is that a sign of a bad cap? Thanks

  • Buck Pomerantz from Crutchfield

    Posted on 1/23/2017 9:54:19 AM

    Dan, I don't know what speed is normal for your particular capacitor, but the load provided by the multimeter itself will drain the voltage from the capacitor. And charging and discharging a capacitor repeatedly while out of circuit will eventually wear it out.

  • Deejaydque from NSW Australia

    Posted on 2/8/2017 4:36:48 AM

    Hi, I have a retro fitting situation for a 8 farad cap. Car audios will benefit from a cap in some instances. My question is, could i use the cap to assist with high current draws from high flowing fuel pumps in my vehicle that draws alot of current/voltage? I have 3x high flowing fuel pumps currently hired wired with 3x 60A relays to 3x 20A fuses to a power distribution box then direct wired to the battery. I want to install the 8F Cap in-between the power distribution box --> to the + battery terminal. Will the cap work in this situation and are there any dangers/factors in this retro fit?

  • Buck Pomerantz from Crutchfield

    Posted on 2/8/2017 11:51:27 AM

    Dee, I'm only familiar with using an automotive capacitor to smooth out voltage fluctuations of an amplifier's power supplied by the vehicle's electrical system. I really can't tell you if a capacitor will be of any use for a fuel pump - or three. And the use of 60A relays along with 20A fuses is confusing - as is the need for filtering the power supply of a pump.

  • Herb from Vienna

    Posted on 2/9/2017 7:09:38 PM

    Should I use a cap even if I'm running 0awg power wire on 1000 watts

  • Buck Pomerantz from Crutchfield

    Posted on 2/10/2017 12:39:25 PM

    Herb, A capacitor helps when a vehicle's lights dim along with loud music, so unless you're in that situation, there's no benefit in adding one.

  • Jim from Mount Airy, MD

    Posted on 2/18/2017 7:48:18 PM

    My touchscreen head unit reboots when I start the car. Installing two 2200uF capacitors (in parallel) to the red ACC wire (in series with a 1A diode) keeps the head unit on for about 10 seconds after switching the ignition off, but it still reboots when cranking, presumably because the starter causes a voltage drop. How much capacitance is appropriate for the yellow continuous power wire?

  • Buck Pomerantz from Crutchfield

    Posted on 2/20/2017 9:50:43 AM

    Jim, Rebooting when first powering up is a normal function of a lot of receivers - it's a way for the internal computer to operate properly. I've never heard of using capacitors in the manner you describe for the reasons you state. If you want your receiver powered continuously, you'll have to use a separate battery.

  • Ben Kramper from overland park ks

    Posted on 3/2/2017 4:46:20 PM

    Do i put the power cord from my LOC onto the positive terminal of the capacitor also?

  • Buck Pomerantz from Crutchfield

    Posted on 3/3/2017 9:48:20 AM

    Ben, Most people use a distribution block to wire the positive power leads of multiple devices in a system. But if your capacitor has room in its terminal system for a low-current device like an LOC, then it's probably alright to use it.

  • Aldrin Ibarra from Cheonan, South Korea

    Posted on 3/3/2017 10:18:56 AM

    Hi...! I have a lp1000.1d hooked in a 10amp (15amp max) battery charger as an audio set up in my workplace... Problem is that the battery charger can't provide enough power for the amplifier when it hits bass notes... Can a 2f capacitor directly connected (in parallel) between the battery charger and the amplifier solve the problem...? I don't consider using a battery because it's very heavy... I can't either buy a high current DC supply because it's very expensive... I hope you can help me with this... Thank you...

  • Buck Pomerantz from Crutchfield

    Posted on 3/3/2017 1:47:54 PM

    Aldrin, If you are trying to run a Skar Audio LP-1000.1D from a 10-amp battery charger, you will find it won't work. That amp will try to draw up to 90 amperes of current which that system can't provide. All adding a battery would do would be to drain the battery along with the charger. If you want to use that amp at home you'll need a 12-14 volt DC power supply (not a charger) capable of supporting a 90-amp draw.

  • Novice

    Posted on 3/12/2017 9:02:50 PM

    I used a rockford 1.0 farad cap in my car audio setup for years. I disconnected and uninstalled everything a few years ago and recently stumled upon the capacitor. May be a silly question--but better safe than sorry... is this thing dangerous? Does it still hold a charge? Does it need to be discharged? A friend of mine wanted it but I am afraid to give it away for risk of injury.

  • Buck Pomerantz from Crutchfield

    Posted on 3/13/2017 10:24:04 AM

    Novice, A capacitor could hold its charge and possibly be dangerous. To make sure it's not, discharge it. Touch the two conductors of a wired light bulb or resistor (20 ohms, 10 watts for example) across the cap's terminals to discharge it slowly and safely.

  • Shay from Telford PA

    Posted on 4/12/2017 11:32:40 AM

    Hello. Great article. I have 2 JL 1000/1 amps powering 2 JL 12W7s, 2 JL 300/4 amps powering 8 6.5 JL 5 Series door speakers. Total system power is currently 2600 watts, but the 2 JL 300/4s are gonna be upgraded to JL 600/4 because the door speakers can handle more than the current 75 watts they are getting. So, system power will eventually be at 3200 watts. I just ordered an overpowered XS power D6500 battery and I currently have an Ohio Generator Alt cranking 320 amps installed. My question is this, should I use the XS Power battery as a secondary battery and not install my Stinger 505 Cap, or use that XS Power battery as the main battery for the entire vehicle and use the Cap? Any other advice would be great as well! Thanks a lot!

  • Buck Pomerantz from Crutchfield

    Posted on 4/12/2017 4:05:17 PM

    Shay, For playing music, I think that your high-output alternator ought to support your system using a single battery and no cap. If you're competing by playing loud bass burps, however, you may need the second battery and capacitor.

  • Mike from Dickinson

    Posted on 4/13/2017 11:59:06 PM

    I'm installing a capacitor do I need a distribution block or can I wire battery to the capacitor and then off the capacitor to the amp on the 12v + side of it

  • Buck Pomerantz from Crutchfield

    Posted on 4/14/2017 11:07:00 AM

    Mike, Yes, you can wire your capacitor without a distribution block as you describe.

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