http://forum.sounddomain.com/forum/ultimatebb.cgi?ubb=get_topic;f=3;t=017893#000003

found this while surfing for help with installing amplifiers ...

the whole dimming lights and adding a capacitor will help = false ...

you thought they really reached a conclusion there? seemed more like a difference of opinion...

Eh?

Says who? As an electrical engineer/computer scientist, I have to say that caps definitely work...

oh by all means they <i>work</i>, I think the question is really just how effective are they at stopping one's headlights from dimming.

I think there's a reason their called Stiffening Caps,
not
Caps to keep your headlights from dimming

The idea behind caps is that they are supposed to store electricity so that when the amp is pushing hard it gets a constant source of energy from the cap instead of relying on your alternator to supply it. The problem comes when people don't understand the math behind using different sized caps (i.e.: someone buys a cap with a max of 500 watts and is running a 600 watt amplifier at full blast) then yes you could theoretically still see dimming lights. That or they wired it incorrectly. However, wired correctly, and math done properly, caps work just fine. Whether you actually neeeeeeed them or not is a whole different story. If you like dimming lights then you should be fine. :) Personally I am running one MTX amp to 2 12" Infinity reference subwoofers, and a set of 5 1/4" infinity reference components up front, and I have had it at full blast and haven't seen any dimming at all........yet. :)

yada, yada, yada...

i know a guy who has a alumapro 15 farad cap for a 1800 watt system and his lights still dim!! and yes, everything is wired perfectly for the stereo... he keeps buying bigger and bigger caps until he got the alumapro, hahaha. he has finally given up and has started to listen to me...

the fact that i had 1500 watts and one farad didnt convince him when we first started discussing it...lol

ya ya its a bunch of shit just get ur alternator rewound

Ooooooookaaaaaay, 1800 watts is a bit much for one cap. That type of system should be at 2 caps at a bare minimum. Doesn't sound like you guys did any of the math at all.

Just some quick math here (I'm a little rusty) but this is what I came up with math wise for an Alumapro 15 farad cap for power handling capabilities.

Alumapro 15 Farad cap = 2000 joules capability

2000 joules = .55 watt hours

.55 watt hours = 550 watt power handling capability (1000 watts in a watt hour).

So it sounds like at BAAAAAAAAARE minimum your friend should've have at LEAST used the Alumapro 50 farad (or 8000 joules power handling) cap and probably should've added the Alumapro 15 on top of it just for precautionary measures if he didn't want dimming lights.

sounds like Sacremento M3 has got it down pat! hahaha...

anyone want to tell him?....

Pardon me, it's a simple voltage divider with the headlights having relatively higher resistance wire. The current takes the path of least resistance. Namely, the stereo.

You'd be better off putting the capacitor on the headlights.

werd...

Jim if you're running a straight power wire from the battery to the cap to the amp, where do the headlights come into play? Am I missing something in my electrical diagram there?

Theoretically here is what happens. I *could* be wrong. We'll assume the car is turned on and using the alternator for current. Current flows from alternator, through battery, to all electrical equipment in car. Normally there would be enough current to supply everything without interruption. However, Guy-A buys super nice sound system with no capacitor to run large amps. Everything hooked up, current still flowing from alternator through battery to all electrical equipment. New equipment has a variable rate of current draw (depending on volume thus power required to get *louder*). The louder the stereo goes, the more current the amps require, thus the more current they *request* (these terms could be more appropriately labeled by someone who actually knows what they're doing with electricity). :) With no capacitor in place it is not that current is *choosing* the path of least resistance, it's that it's being *pulled* from the other sources to provide the appetite of the amps that need it to run at the level requested by Guy-A (who controls the volume, thus energy required to power speakers). With a capacitor in place energy is stored for those temporary moments when the current request of the amps is greater than normal. However, if you are constantly running your stereo at full blast and have installed a capacitor not capable of storing enough energy to provide that type of current, then you will still draw the current right through the capacitor as though it were transparent to the system. Anyhow, that's what I can theorize. Take it or leave it. :)

In electricity, the current is ALWAYS defined by the load.

Your lights (except at initial startup) draw current in a manner very much like a large wattage resistor. Two 55w lamps = 110 watts. For simplicity's sake, lets round up to 120 watts to account for power dropped in the wiring. 120 watts supplied by 12 volts equals 10 amps. That is a constant.

The amp is a variable. With lots of bass at max volume the load almost appears as a zero ohm resistor and can draw hundreds, maybe thousands of watts. Lets say that in a 1200 watt stereo draw the current would be 100 amps. Your alternator can only put out about 890 so the battery supplies the rest for the momentary load. Stereos rarely draw maximum wattage verymuch as a percentage of their duty cycle.

When the amp asks for the sudden inrush of current, the wire to them is pretty large, typically 0 or 2 gauge. Sometimes 4 gauge for smaller amps.

Your headlights are running on 18 gauge or less and offer a relatively larger resistance to current flow. When the amp requests current from the alternator and battery, it WILL get it and from any source available, including that current that was supposed to be going to the lights. Normally in a healthy charging system with a voltage regulator in good shape and good contacts on the alternator brushes and clean, properly sized connections on all components, everything behaves nicely. But if the voltage regulator is weak, the brushes worn, the commutator pitted, the battery cables corroded, the power splitters undersized or the cable trimmed in diameter to fit an undersized ring lug, then the charging system cannot supply enough instananeous inrush current and the amp will steal from the lights. Simple voltage divider.

The reason I state that the cap would do better on the lights is because the cable runs to the amp are usually very short. If the connections are done correctly, the battery can supply all of the current the amp will ever need. The lights on the other hand, are 20 cable-feet away and on small gauge wiring. The lights are what could benefit from a capacitor, not the amp.

werd

Ahhhhh Jim,

You are used to the battery being in the trunk, not under the hood where they are in *most* cars. This can typically result in a 15-20 ft power cable as well after being ran from the battery through the firewall down through every nook and cranny to where the amp is located in the trunk.

But again Jim, your point only further illustrates what I've already said. A capacitor is a storage tank. It stores electricity. Bottom line. If you hook one up *correctly* (make sure to do all the calculations, proper wiring, etc etc) then your system will never draw more than what the capacitor holds and thus you will never experience that inrush of current from the alternator through the battery to the amp. Instead the amp goes and gets from the closest source (i.e.: the capacitor) until it can no longer get what it needs from there and moves on to the next place it can meet it's needs. Again, it will never go outside the capacitor if you have done everything correctly.

Also, I'm not sure the cap would work well wired to the lights either, for the simple fact that if you are drawing that much current for your stereo system, the cap never receives enough to stay charged to provide the lights with a constant source of current. But it's just theory right. :)

Large power requirements are minimal in most systems. Capacitor calculations are sometimes not as straightforward as they seem as you have to 'look' into the amp to determine what kind of resistive, capacitive and inductive network you are creating.

Another thing is that most people use caps because they believe that their alternators are undersized to provide the inrush current. They usually are wrong and the battery is perfectly capable of doing the right job if the supply cable from it to the amp is sized properly. In fact, an undersized alternator can be damaged by placing a capacitor into the system. Call Rockford-Fosgate and ask them for their opinion. I think they might actually have a technical bulletin on the subject.

Capacitors are minimally helpful in cases where they are not solving an electrical problem caused by complex multi-amp, multi-speaker arrays. But they generally do little harm and are nice eye candy.

All I was stating with the comment about the headlights getting the cap is that they tend to be the equipment most affected by voltage sag. And it does them absolutely no harm. At least in straight light bulb applications. Some of the HID systems don't like it at all.

It's actually very easy to figure the amp calculations and what you would need to cover your system. For example take

13(volts from battery) x 40 (add the amperage of your fuses together in your amplifier/s 2x20 lets say) x 50% (amplifiers give off a certain amount of heat making them not the most efficient electronic equipment in the world, some are better than others, but on average you can say about 50%) x .707 (this will give you the actual raw power you can be guaranteed all the time divide by how many channels your amplifier is and you have how many watts you will be using all the time. So it looks something like this

13x40x.5x.707 = 183 watts. divide by a 4 channel amp gives you roughly 46 watts per channel.

Now you can pretty easily calculate the amperage of your amp from that simple addition of the fuses in your amp. So on this particular amp you would be using 40 amps or about roughly half of what your alternator can put out (give or take). So in this case yes you're probably right. Now if you have 2 40amp amplifiers you could now be stressing your alternator and that's not a good thing. This is where caps can come into *useful* play as it were. You now have approximately a 367 watt or lets just say 400 for round numbers purposes. In this case a 500 watt capable capacitor should suit your systems needs just fine.

Most single amp systems will never need a capacitor (i.e.: why I'm not running one because it just adds more connections to the mix which can result in lost power). If you are running one amp and you are seeing a lot of dimming in your vehicle you either have one very kick ass amp, or a problem with your alternator or battery.

dang it, so who's right on this subject ...???

Jim or Sacramento? It seems as if you are using the right gauge wire, good alternator, no cap is necessary ... and if you have dimming lights... something else is a matter.

NoSoup4U

We're both right. We're both essentially saying the same thing. If you're not running a very power system you wouldn't need a cap, as it wouldn't be useful, no point, and it's just an extra connection you don't need.

If you're running a powerful system that necessitates a cap you probably want to use one.

If you're not running a powerful system and you're seeing dimming lights then you probably have a bad connection, corroded battery terminals, bad wire, alternator going bad, battery going bad, etc etc, something like that.

ok.