I dunno I have a cap on my system and I definately noticed a difference in my lights dimming when the woofers hit. As for Ohms Law, and Kirchoffs Voltage equations etc, I was a Comp Eng so I do have experience with them. but caps although I agree that if its a small quantity it won't be a difference, but they can help. Note the word HELP. Not solve problems.

 

Well this is Happening in a Ford F-150 and My Freinds wants to do the Optimna thing which one should we be looking at being the yhave like 20,0000 diffent ones

 

Yellow Top. If youre getting a high output alternator you should get an optima for sure. Standard batteries can be overcharged and explode. Optima makes the best fricken batteries, a high output alt and a yellowtop will STOP any dimming whatsoever. However, light dimming can be stopped by a cap.

 

Alright, here's the low down...

For this:

V = Voltage
I = Current
R = Resistance
P = Power

The voltage in an a system (your car) is constant due to everything being in parallel. The current changes and in the DC world is what really counts. Power varies with current, not the voltage. The current and power draws are directly related the resistance of the device. Due to Ohm's Laws which state:

V = IR and P = IV... Notice, P and I can be interchanged (they're linear) when V is constant.

So now, when you're Amps "hit" they drop the resistance to allow current flow so that the power goes up, keep in mind, power is what makes things happen. Remember, the power here depends only on the current, voltage stays the same idealy. Therefore, the maximum amount of power the battery can deliver will be reached at a certain point and the voltage and current will drop, dropping the voltage, and in turn, making everything dim(like bobbytonic said.) When the voltage drops, the amps, and everything else are instantly starved of current because they have a set resistance, and now a set voltage lower than the normal. So:

Normal:

V = IR so: 14.5 = I * 50 ohms. I = 14.5/50 = 0.29A of available current

Dropped voltage:

12 = I * 50. I = 12/50 = 0.24A of available current

See? Less current available.

Now, what capacitors do is try their damnest to keep the voltage level constant. They WILL NOT provide the amps with more current, when wired in parallel like they should be in these applications. They help the electrical system deliver more current to the amps by not allowing the voltage to drop as drastically.

On that note, and using the example before, if your electrical system has a max current rating of .29A(not at all realistic, but go with it) and the amp drops the resistance to 40 ohms.

V = IR so: V = 0.29 * 40 = 11.6 volts, Oops, there's that pesky voltage dropping, making everything dim. EVEN WITH A CAP.

Now, if you up your battery is upped to one that can put out say, 0.5A(really unrealistic, just deal)

V = 0.5 * 40 = 20... you're still fine.
^This equation isn't valad though because the voltage wouldn't go higher than say, 14.5 giving you a max current draw of 0.36A peak, the device wouldn't use all 0.5 amps at this point.

So basically, the Capacitor will help your car reach it's maximum output load but will not help past that. Most people don't use nearly enough capacitance either, I'd would say it would have to be a farad for every couple hundred watts you're running.

Now, Battery VS. Alt. discussion. The battery is what releases current to your system, and regulates the voltage, period. The alt just charges the battery. I'm pretty sure, correct me if I'm wrong(Sacs,) an altinator is actually an AC current source that goes though a half wave rectifier and charges the battery in a pulse like manor. Which is totaly useless in the world of DC, the battery takes the pulses and uses them to charge itself and has a DC output (Like a cap does for voltage, the battery does for current.)

So, the battery is what you should upgrade first, to up the max power output. If the alt can't keep the battery charged enough to stop the dimming, get a bigger one of those second, if it's still dimming get cap(s) to even out the voltage last.

There, now you've all had a freshman level DC Circuits lesson. Any questions?

Oh and bobbytonic, 1 Ohm loads are far more power hungry than 4 Ohm loads, work it out with the Ohm's Law equations. It'll turn out to be 4 times the current and 4 times the power I bet ya.

 

That's precisly what I want is more power =]

1000 watts@4ohm is going to require more power to produce then 1000 watts @ 1ohm

 

Once again..

When the vehicle is turned on as long as the voltage being supplied by the alternator exceeds the internal resistance of the battery, it simply charges the battery. When the vehicle is turned on, the battery does not supply anything, it is actually a load on the charging system.

Alternator 101:
A basic alternator has 2 main electrical components. The rotor and the stator. The rotor is the part of the alternator that is spun by the drive belt. There are a group of electrical field coils mounted on the rotor. The stator is the group of stationary coils that line the perimeter of the inside of the alternator case. When current is flowing in the rotor's coils, they induce current flow in the stationary coils. The induced current (and voltage) is an AC current. To convert this to DC, the current is passed through a bridge rectifier.

So we now have 14.4(nominal) volts of current coming from the alternator. On my car, the main power wire goes to the fuse box, then to the battery. So the car now has a charging battery, the vehicle, and your system running off of the stock Honda 80amp battery. A battery is not a transformer, it doesn't have the mystical power to convert AC-to-DC, at least not in a car.

A capacitor will band-aid alot of people's dimming issues, but it won't fix the problem at hand which is a sever lack of source power for a high powered system.

 

I don't mean to be an *** but you seriously hafta be a sh*t head to argue with an electrical engineer about basic electronics. And, some of it I agree with you on, you just really love to argue.

Watts are used to measure power. 1000 watts is a 1000 watts. That's like the old question, what weighs more, a ton of bricks or a ton of feathers... they both weigh a ton. You have to look at it like, an amp that makes 1000watts at 1 ohm that's running at 4 ohms will use a lot less power and put out less power. Which is what I was talking to Rem about... all my amps are running 4 ohm loads therefore, using less power.


Bull. A battery is not a load of any kind, at all. Without it, the voltage would depend on the speed of the altinator turning and it would be the positive parts of the AC wave cycle. Edit... unless it's a full wave rectifier in which case, it's just the upper parts of the AC wave and looks a lot like really messy DC.

What the hell does "as long as the voltage being supplied by the alternator exceeds the internal resistance of the battery" mean... that makes noooo sence.

No sh*t. I've take many a class about AC and DC generators and motors. It's not true DC power though, It's the positive parts of the AC sine wave. Edit... it could be a full wave recitifer in which case it would still be AC but it would look more like really messy DC.

No, the voltage comming from the alt. depends on the speed of the pully turning it. And yes, the battery is where you get DC from, not the alt. It's the same principal of how a cap doesn't want the voltage to change rapidly... the battery doesn't want the current to change rapidly, giving you... drum roll... DC CURRENT. This current is then used to charge the battery which holds 12V (rated) as a spec. of the battery. Go outside, start your car and detatch the battery... see what happens.

Yuh, exactly what I said.

Laws don't lie, that's why they're laws. I think maybe you should accept that you wern't totaly right about some of this and learn something from it and realize we're sayin the same thing about the rest of it. We'll get along better, I promise.

 

It has a built in voltage regulator. Ok, here is a great article on the basics of the charging system in a car. Basics of charging system

So....
The regulator keeps the voltage at a constant 14.4 or at least tries to. 14.4 volts is higher then the 12.2 volts of a battery. So when the car is on, electrons flow in the downward gradient to the battery.

I can't grasp why you don't understand that the power comes from the alternator and not from the battery when the vehicle is turned on.

 

Ok, now I can see where you get your info... I don't agree with that site totaly. A battery isn't a drain on the system when it's charged, it will release current when the car is running if so needed, and if your lights are dimming, it's probably needed. It does help regulate the current to a cleaner DC. Also, electrons flow against current. Electrons have a neg. charge and are what's actually moving but current is defined as the movement of positive charges. Makes no sence, I know.

I do grasp that the power comes from the alt. Fully, I'm not an idiot. Did you skip this section?:

That's what I've been trying to say the whole time. The battery is a DC regulator on it's own, in addition to the one on the alt.

I really hope that you can learn something from all this. If you can't learn from what I have to share then this probably isn't the place for you.

This forum is a learning community, people come here to learn about a huge variety of things. Hell, I know I've learned more in the months I've been here than any professor has taught me in the same time period. Being wrong about things helps you learn more than being right about them. Trust me, I do countless labs where they trick you into being wrong about things so you have to learn to get the right outcome. Look, I don't want you to leave or anything, I hope you stay, and I hope you can learn from the HUGE amount of knowledge people around here have to share about almost anything, It's what we're all here for... to teach and to learn.

Also, I was wrong before... when the engine spins faster the frequency of the AC wave goes up, not the voltage of it. It's pretty late, I'm pooped. Wait, maybe it does... I'm drawing a blank right now.

 

so after reading all that interesting information lol the question i have been stuck with still doesnt seem to be answer though its 20 mins till 1 in the morning.. i just could have missed it.

i have an 130 amp alternator..aftermarket of course
2 year old battery...
the only thing i really run hard is my amp for the subs... which is a Audiobahn A4002T
{Input Sensitivity: 200mV ~ 8V
THD: <0.05%
Variable Low-Pass Filter: 40Hz ~ 120Hz
Variable Bass Boost Control @ 45Hz: 0 ~ 18dB}

my subs are 1 audiobahn AW1251T running at 2 ohms at 200 rms.. and the other is some piece of MTX Road Thunder junk.... which makes no differnet to my set up... but
to the question

idle... my lights dim...acceleration.. the brighten
idle...weak a/c-heat...accel....blasting! lol
hit me with some answers!