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Cap or not to cap

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  • Cap or not to cap

    I and a advanced/novice when it comes to stereo stuff...I know enough to do the job and if I don't I know how to find out. I am installing my second is my question. I see tons of arguments one way and the other. What is the beef with capacitors? I have never used one but my new amp is going to be running to the speakers at 1 ohm and I am getting support saying I should others saying they are why are cap's crap? I feel like I am in a Dr. Seuss book

    Should I would I use a cap?
    Could I should I not use a cap?

  • #2
    I found a bit of info that might help from ......

    V = IxR. Where: V = Voltage I = Current. R = Resistance

    With a power amplifier, resistance varies with the volume and frequency of the music. As the resistance fluxuates the amp draws more current and expects the voltage to remain the same. It is the regulator on your alternator's job to make sure the voltage stays the same by dishing out more current when it is needed. If the regulator cannot react fast enough to the change in resistance, the voltage will drop.

    This means, each time there is a bass thump, the voltage will drop slightly until the regulator catches up. You will recognize this at night by seeing your lights flicker. The regulator is fast acting, but not as fast as a double bass drum.

    A capacitor tricks the alternator's regulator into thinking there is less resistance while the amp is in a low-output state by storing electrons and creating a faux current. When the amp changes to a high-output state, the capacitor is quickly drained and begins to charge again when the amp switches back to a low-output state. This happens very quickly...such as between bass drum kicks in a fast rock song.

    The result is a smoother current draw from your alternator which prolongs the life of the regulator. There is also an audible difference in music because the voltage will not fluxuate as much and your amps will get the current they want...when they want it.

    However, many new amps use regulated power supplies to combat this fluxuation in voltage. This means whether your alternator runs at 15 volts or 11 volts, the amp will operate the same. Essentially, they don't take advantage of the extra voltage when it is there. For this reason, a regulated amp will have higher SQ while an unregulated amp will have higher output while the car is running (14v) vs. while the car is not running (12.5v).

    Still, a regulated amp will cause a fluxuation in current even if it unaffected by the drop in voltage meaning a capacitor can still help your electrical system.
    Last edited by RAWPWR; 07-15-2013, 03:55 PM.


    • #3
      i had always wondered, but never enough to research. Thankyou RAWPWR!
      Originally posted by ClockWorK
      Remember, as soon as you make something idiot-proof, they will come out with a better idiot.


      • #4
        Actually, I dispute all the above (sorry RAWPWR).
        There is no resistance change nor regulator trickery nor unused "extra" voltage.

        In brief, a cap is merely a store of energy.
        So is a battery.
        But if your amp is a long way from the battery and you have a burp that causes a big voltage drop between the battery and amp, a cap near the amp will supply some energy.
        However a (2nd) battery near the amp will do the same, and since a battery is at least thousands of Farads, why buy a 1F etc cap when a 12V 1.2AH battery holds far more energy?
        One reason is to protect adjacent AGM battery(s), but only applies to amps that are typically above 3kW output (RMS of course!). There are also other reasons though they rarely apply to audio set ups.

        And interesting read is Richard Clark. Richard and David Navone pioneered car audio implementations and introduced "stiffening" capacitors.
        In the years since, Richard saw the fallacy of caps and now debunks them. (But too late, bad info often outlives the truth.)

        And if you are after (peak) SPL, most I know of advise against caps.


        • #5
          I have a 1F cap, and a Stinger SV35 battery, on the amp side of my starting battery isolator solenoid. I could not find closure to the debate so figured, what's an extra $100 just in case. So far I have not had any negative impact.


          • #6
            Alas many do not like spending $100 for no gain, else inferior gain.
            As I see it, $100 is an extra battery which can be used for emergency cranking etc. But I'd probably find better uses for my "spare" $100.


            • #7
              I am not personally a proponent of caps most of the time and don't use one myself, but they don't hurt anything to have. The worst case scenario is you waste some cash.

              The debate can rage on forever, but I always say upgrade everything else first. Battery, cabling, and alternator and if after all that you have dimming of your headlights then try a cap or extra battery.
              Computer is in the car, but in a very "raw" install right now.

              Worklog - here


              • #8
                Trust me, the debate is closed.

                Maybe I can paraphrase - except as I mentioned: eg, a cap to protect an AGM (at the expense of peak SPL) or where batteries are not practical etc; and some limited applications - a battery beats a cap hands down. IE - why spend on a cap when a cheaper battery will do better?

                If you already have a cap then IMO you may as well use it assuming it doesn't add extra path resistance and on-selling is not worthwhile.
                But to buy a cap or add a cap for low power amps (under 2k-3kW) irrespective of battery type is pointless.

                As FockMasterDan and most knowledgeable people will say - upgrade everything else first. As a general rule that means the big-3 or big-4; upgrading the alternator (before adding batteries depending on why the extra voltage or current is required); adding additional batteries if required (eg, near the amp for burps; via isolators, etc).
                And if adding caps to un-dim headlights, place those in the light's supply (usually before the relay or switch), but again, a battery will do better.

                AFAIAConcerned, apart from the exceptions I outlined in this thread and elsewhere, until someone starts defining burp/sag durations etc OR provides sample CRO waveforms of amp voltage sags (and comparing a 1.2AH battery etc interchanged with a 1-40F cap etc), there is no debate.
                All these pro-cap experts and manufacturers and yet no supporting CRO etc proof? Doesn't that seem strange?

                I can understand why many are confused or convinced. But why not add a ferric or gold battery base or tray to improve ripple smoothing and add battery capacitance? Gold-plated trays are available for $100 upwards. So too are gold amp housings.


                • #9
                  I actually have a cap that I got second hand from someone I know years ago and it's still sitting on a shelf. I could easily install it, but why?

                  I will say that space and ease of install could be potential reasons to use a cap over a battery. It's pretty easy to shove a cap somewhere in the trunk for someone that isn't up to fitting a battery in somewhere. I'm on the other end of the spectrum though, I just turned my whole trunk into an electronics bay that includes my primary battery for the car.
                  Computer is in the car, but in a very "raw" install right now.

                  Worklog - here


                  • #10
                    With low quality unregulated amplifiers Caps can make a difference. Caps have never been considered the correct way to do things. They are considered a band-aide and in today's high quality, high output regulated amplifiers they are almost totally worthless if the system is setup right. Some competition systems in the past incorporated CAPS more as an insurance than a need.

                    Capacitors discharge much quicker than a battery can but they generally don't hold as much capacity as a battery. If you have a high powered system the proper way to do this is to have a battery as close to the amplifier bank as possible with as big a wire as practical to the amplifiers. In some competition systems you will see a solid bar used instead of wire for the majority of the power feed but a high purity copper wire with many strands is much easier to work with.

                    If your power wire is under sized you can get a severe voltage drop at the amplifier during some deep bass notes. A capacitor can be used to diagnose an undersized wire but should not be used instead of a proper sized wire. If your system works well with the capacitor and sucks without it then your wire is undersized and potentially your battery is either old, or under sized as well. The PROPER fix for this then is to increase the size of wire used to feed the power from the battery to the amplifiers and make sure all ground paths have been upgraded as well. (Battery to block and block to body or whatever method your vehicle uses to ground from the battery to your amplifiers. If you run a wire directly to your battery then that wire needs to be the same size as the positive wire.) No such thing as too big a wire.

                    A capacitor can also be used to get rid of system noise but again this is not the right solution. The right solution is the proper sized wire and proper routing. Sometimes a bad component can also cause noise.

                    Main reason why this doesn't work with high quality amplifiers is they already have large capacitors incorporated into the power supplies and having an external capacitor is a total waste.


                    • #11
                      I have a cap for sale, used for 6 months, but about 9 years old, stored carefully in the closet, looks like new......sorry wrong section to post this in......

                      BTW, when I did try it, it appeared to add a lot of watts to the system. It seemed on par with the % of increase I got from my STP stickers for adding HP. I think they must work on the same technology....
                      My 2007 Ford F350 Work Log located HERE


                      • #12
                        I'm the deep pocket overkill guy I guess. I got an 150 amp alternator, isolated spare battery just for amps and pc, 1F cap, extra parallel grounds to HU, short run 1/0 awg wire with everything in trunk. All that for only 800wrms, sound processor, and pc. Not only that, but I placed dynamat squares anywhere I thought might transmit vibration, not for full coverage but rather to absorb outside noise. I still have to install the pc, but will probably never be finished messing around, as it is a hobby and is fun.


                        • #13
                          Originally posted by PhilG View Post
                          I have a cap for sale, used for 6 months, but about 9 years old, stored carefully in the closet, looks like new......sorry wrong section to post this in......

                          BTW, when I did try it, it appeared to add a lot of watts to the system. It seemed on par with the % of increase I got from my STP stickers for adding HP. I think they must work on the same technology....


                          • #14
                            Better make sure to grease the muffler bearings and change the blinker fluid before adding the flux capacitor. Once you add it the bearings will vibrate and cause corrosion and the blinker fluid if not changed will start separating due to the pounding the Capacitor allows. Blinker fluid that separates is bad news because your blinkers will turn blue and people will think you are an emergency vehicle and you will get a ticket.


                            • #15
                              So it seems that the debate is closed for most.

                              PhilG probably mentioned the real power adder, namely the STP sticker (since we all know a cap does not create power...).
                              And does a cap "add power" if it decreases peak SPL? And if it does, then since a battery stores far more power than a cap...

                              And if you read the audio forums, you'll read how a cap "puts more strain" on the charging system. (That's bullsh - a cap like a bigger or more batteries will DECREASE the "strain" on a charging system.)

                              So, apart from a cap being used to protect AGMs against big surges, or when space is limited or an isolator is undesirable, then a bigger or more batteries is the superior solution.
                              Adequate or improved wiring and a good alternator are the first things to implement.
                              Then whether bigger or more batteries else a cap helps depends on the system and what is desired, and that's where I find audio forums and other discussions full of contradictions and misunderstandings.
                              On another respected 12V & audio forum I once suggested a proper evaluation using a proper step function to simulate big audio amps (since they use SMPS) and s-domain (time domain) techniques. Alas that seemed to complex for most (not surprising since some reckoned an amp's resistance changed as its current varied!) so I didn't continue. Later however I did an evaluation with a mate that still used and understood s-transforms and we concluded that my arguments were correct (especially for long burps which cap enthusiasts conveniently seem not to define nor consider).

                              As for old caps that have dried out or failed... ouch! - they are worse than failed AGMs.