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Capacitors: What You Need To Know Before Buying.

24591 Views 59 Replies 24 Participants Last post by  Christianbazin
So, you just installed your new stereo, but you notice your lights dim when the bass hits?


You're buying parts to build a system and youre worried that your lights will dim because (insert name here) said that you need one?

If you answered yes to either of these questions, a capacitor is not the answer to your problems.

A capacitor acts like a small battery to filter small ripples in your electrical system, it discharges when the input voltage drops below the charged level of the capacitor to keep a constant voltage.

Now you're probably wondering why they wont fix your problem if they do what I just said, right?

Well, here is your answer, a capacitor simply will not support any electrical components placing that much demand on your electrical system. Sure you could get a huge capacitor. The price of one of a capacitor large enough to adequately support that substantial of an electrical system just isn't worth the difference, and you're still not fixing your underlying problem, an inadequate charging system. Once the capacitor is discharged from being over extended from being used improperly, it becomes even more of a strain on your already limping electrical system by trying to recharge.

Now you ask, if a capacitor wont fix my problem, then what will?

Well, there are three steps that you can do to combat your inadequate charging system. Steps 2 and 3 are interchangeable, I would recommend them in the listed order, but it isn't as important as the first.

Step one: upgrade your big three wiring, these wires are:
1. Alternator to Battery (+)
2. Frame to Battery(-)
3. Engine to Frame or Battery (-)

See the following link for more detail.
Big Three Upgrade: How To

Step Two: Higher Output Alternator.
Simply replace your factory alternator with an alternator that put out more amperage. The most common and cost effective is the AD244 from the newer full size trucks.

See the following link for more information about the swap.
AD244 Upgrade: How To

Step Three: Add Another Battery
Just like it says, add another battery, you should use at least the same size wire that you used for your big three, if you have any considerable length of wire to reach the new battery, you need to fuse the wire at each end to help prevent any electrical fires if the insulation should become compromised.

If you are dealing with batteries of different types and or ages, an isolator should also be used to prevent premature battery failure, but this will also cause a half volt drop across the isolator.

This should fix your problems for up to a moderately high powered system (2000-4000 RMS Watts) if it doesn't repeat steps 2 and 3 and necessary.

Now that you've read why you don't need a capacitor, now you can see what they are useful for.
You already know that capacitors filter ripples in your electrical current from the beginning of this tutorial.
There are sound quality benefits to using capacitors as a filter before your amps. The first benefit is if there is an immediate need for a high current draw such as a bass note with a very fast attack, the capacitor can discharge faster to supply the required current, in addition to the current that is already there from your battery and alternator to keep your amplifiers response as fast as it can be.
Secondly it helps keep voltage spikes from reaching your amplifiers.

In conclusion, unless you have extremely fine tuned hearing chances are, you will never miss a capacitor in your system, but, I will not discourage you from getting one, so long as you are using it for the right reasons, if you are trying to fix a voltage problem with it, you are simply trying to put a band aid on a bullet wound, but if you have a strong electrical system and are looking for something to smooth peaks and provide an additional kick if its needed, chances are a capacitor is what you are looking for.

Happy Building,
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T hate it when TV shows especially give wrong information like that, its mainly just a marketing tool to sell something cheap to manufacture, I would think that the sales stated out using them as I described that they should be, then someone used it for a band aid and it made their dimming less noticeable so they thought it was the cure, so the lower end companies caught wind of this and exploited a lot of sales from people that didn't know any better
Thank you to whoever stickied this
Forgot to mention using relay for switching power if you connect stuff that don't shut off by it self. Most large amps have a relay built in hence the 2 positive wires, 1 gets connected to low current switched circuit. Also over fusing risks burning/melting wires if they get shorted, lower slow blow fuse or circuit breaker is better.
the reason i said 2 fuses is because if you have a battery in the bed, you need to prevent the wire between the batteries fused at both ends to prevent current from entering the wire from both sides if the insulation is comprised, yes a circuit breaker will work in this situation, but they can trip from vibrations where as a fuse will not
I should whip out my super-dee-dooper-awersome drawing :haha: :rotf:
be my guest
I apologize for not making abundantly clear in reply #13 that it was a continuation of reply #11, and for the confusion over it's wording. Reply #13 should start:
"I forgot to mention in reply #11 and the following is in reference to it"
I would have preferred being able to edit directly into reply #11 versus a separate reply, while also using the later improved wording.

I suspect that in reply #16 you are refering to "over fusing" as well as the use of a circuit breaker, in reply #13. If so by "over fusing" I refer to using a fuse of higher amperage rating then is recommended. And breakers often slower to react can allow surges while still limiting the average current, thus better then "over fusing" and similar to using a slow blow fuse. I would however agree, reply #16, more protection where needed is better. With that the current ratings in reply #11, for those that would like to know some recommended values, are from a reference which I use.

My only real contradiction of the original post is: There is no need upgrade the stock small wiring when it is just as easy to go to the source (the battery) or at least to the where the heavy gauge wires (cables) that can handle the current end, when either method will generally do.

If however you are upgrading to a 200amp alternator then go ahead and put in 0000 gauge wire or double up on 1 gauge, it should only help. And if you prefer to change "your big three wiring" as per the original post and it's reference, you might also consider same for frame (or engine block or battery - ) to cab body, if intending to use it for a negative connection (grounding point) for everything.

Again I apologize, for any confusion over my input. Would you please point that thing somewhere else.
you must be vastly confused on the way the automotive charging system works, the battery has to get its power from somewhere, that would be the alternator, the factory 8 ga wire isnt big enough to support much more than the factory electrical system, this is why we upgrade the wire going from the alternator to battery, block to frame and the battery to frame (big three).
8 ga wire is only rated for 40 amps, even the factory alternator puts out 90 so they were going cheap from the factory, so if you upgrade to a higher output alternator you will need even heavier wire.

also 0000 wire is very few and far between in mobile installations and is for the most part impractical to most members on this forum. 0 ga or at most 2/0 is the largest nearly anyone would need.
Capacitors are also less prone to be scrutinized by the police. That "I use that bat to test my tires" crap only works with truck drivers.
never heard of that before, but okay, i guess, dan is the man so ill jump on the band wagon:D
lol. like i said before this was in my honda and i no longer have it. but i know for a fact it helped my electrical system. even if the meter is "not very accurate" at reading precise voltage, it can still tell you if the voltage is dropping or not. and you know the cap is doing something when your meter stops dropping. And even if a capacitor does simply " smooth voltage peaks and valleys " this is better than doing nothing at all. Again, i agree capacitors are not the best way to improve voltage drops, headlights dimming, etc. but they do work. if you have a 20,000 watt system.... then NO a capacitor will not help you. but if you're only running 1500 watts or so a cap WILL help and i know this from personal experience. not from hearing it off t.v. not from a car audio store trying to sell me something, not from a buddy, but from personal experience
how much does a 5 farad cap cost? and then how much does a battery cost? a battery will hold 10+ times the amount of energy of a 5 farad cap for right about the same price, now tell me it isnt smarter to get the battery?
How much does a battery isolator cost though??
depends on what kind you use, but ive seen some for 5.00 and i think 30.00 would be tops for them.
and you don't have to use a battery isolator anyways. it's just recommended if you like to sit with the truck not running but still listen to your stereo for a long period of time.
that is if your batteries are the same type and age though, amirite? otherwise one will always try to charge the other and that leads to premature failure IIRC.
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