Originally Posted by 04xtype04

Import Tuner is a more reliable source in my opinion, plus I have personally tried a couple of the voltage stabilizers out and find they help.

Originally Posted by Mikey

I read the article the OP linked to that supposedly proves that these things work. Here's something of great relevance:

"But the amount by which power and torque increased-0.5 whp and 1.5 lb-ft of torque, on average-is low enough to be considered standard variance in back-to-back testing a 15-year-old car with an impressive history of check-engine lights."

Originally Posted by 04xtype04

Import tuner tested all of them and found they added about 2 or 3 horsepower and increased torque slightly across the powerband

Originally Posted by Thermo

Alfa, maybe I can help with the clarification of things. Please keep in mind that we are now talking on the scale of milli and micro-seconds. Something far faster than you will probably perceive with your eyes.

Lets first start with the purpose of what the various components are designed/meant to do:

Alternator: provide source of power to keep all electrical things in the car running and to provide a means to recharge the battery for any power that gets pulled out of it

Battery: provide an initial source of power to roll the engine, to act as a filter to minimize voltage changes in the electrical system, and to provide a source of power to maintain any electronic memory.

Capacitor: an electrical component designed to minimize changes in voltage by either absorbing or discharging electricity. Can be made to do other functions, but for this situation, this is all it does.

Now lets get into the micro second explanation of what happens with your car. When you open the door (engine is off), the only thing providing power for the car is the battery. Due to this being a chemical reaction, the voltage output of the battery is a constant thing (ie, the voltage does not bounce up and down). This voltage is normally 12.6 VDC.

When you crank the engine over and it fires, the alternator is set up to run at a higher voltage than the battery so it assumes all the load. Should the output of the alternator fall below that of the battery, due to the battery being at a higher voltage, it will take the load (keep this in mind).

Now, for how the alternator controls the system voltage. The ECU looks at the voltage being sent to it and compares it to a reference voltage (internal to the ECU for our cars). THe ECU then sends out a voltage to the alternator to raise and lower the voltage as needed to maintain it at the desired voltage. For the sake of this argument, I am not going to cover the first minute or so of the engine running as this is beyond what we are trying to talk about here. So, I am looking at just the steady state, driving down the highway, condition.

The alternator takes the voltage from the ECU and applies it to the field of the alternator. This creates a rotating magnetic field inside the alternator. This rotating field causes electricity to be generated in the outside coils of the alternator in the form of alternating current (AC voltage, stick with me here). This alternating current/voltage is bouncing between +15 and -15 volts. While still inside the alternator, this voltage is sent to a device called the rectifier. The rectifier takes the positive voltage and sends it straight through and the negative voltage it will invert to make it positive. So, the output of the alternator is "bouncing" between 0 and +15 volts in a modified sine wave (there is more to this and the electrical engineers will know this, but I don't want to make things more complicated than what they need to be and try to break it down to something that others can understand). Just keep in mind that the voltage is only changing at the alternator like this and is not being seen by the ECU (see below) and also is changing fast enough that the ECU can not keep up with the changes.

So, with the alternator trying to "bounce" between 0 and 15 volts, the battery is wired in parallel to the alternator, the two are going to start "sharing" what each one is carrying. Remember I mentioned that the component with the higher voltage will carry the load? In this case, when the alternator is above 12.6 volts (which is a majority of the time), the alternator is carrying the load of the car and also feeding some power into the battery. But, as soon as the voltage drops to below 12.6 VDC, the battery starts taking up the load and powering the car. So, in reality, the electrical system of your car "bounces" between 12.6 and 15 volts. When you connect up a multimeter, it is taking the average of this and will then indicate a reading of 13.7 to 14.4 VDC (different multimeters filter this voltage differently and will therefore give different readings).

Now, lets add a capacitor to this equation. In short, we are now going to have 3 power sources "fighting" to take the load. This is what it really turns into as you will see. The big thing to keep in mind is that the capacitor will respond faster than the battery to changes in voltage due to capacitor storing the power as a field vice in a chemical reaction. The starting of the car is essentially unaffected. That all remains pretty much the same. So, lets move on to going down the highway.

The big thing to keep in mind here is the capacitor is going to fight to keep the voltage at 1 specific value and not allow it to vary at all!!!!!!! With the engine running, the capacitor is going to do this at a voltage above what the battery is at. So, for the most part, the battery gets removed from the 3 way power fight. So, now we are just dealing with the capacitor and the alternator.

For the sake of argument, I am going to start at a predetermined time where the capacitor is charged to 13.7 volts and the alternator is at 13.7 volts too. As the alternator voltage tries to rise above 13.7 volts, the capacitor is going to suck up this extra voltage and force the voltage t othe car to stay near 13.7 volts (keep in mind that as this happens, the capacitors voltage will rise slightly but for sake of argument, it is constant in this case). As the alternator's output falls below 13.7 volts, the capacitor will now release its stored power to try and maintain the voltage at 13.7 volts (Yes, the voltage will fall slightly as the capacitor discharges). The battery only steps in if the capacitor voltage were to fall below 12.6 VDC. This is where the size (farad rating) of the capacitor comes into play as the larger capacitor will have more power storage than a smaller capacitor. Therefore, the larger capacitor will be able to maintain the voltage near one value better.

To give everyone something that they can relate to, if you remember driving in a car with a cheap radio in it, some people could hear a humm coming through the radio. That is this voltage oscillation that I have been trying to explain. It can range from a few hundred oscillations a second to tens of thousands a second.

Is there more to this. OF COURSE. I have simplified this to make it something that the average Joe can understand. If you want to know more, I will discuss it in a different area as you can get into a lot of different situations where something as simple as the placement of the capacitor can affect whether it is acting as a true power source or acting to filter more and vice versa. Also, I will admit that my explanation of how the capacitor absorbs the power is very simplistic. But, I figure most people don't want to get into how the wiring is dropping voltage due to excessive current and ........... (I can see the eyes rolling into the back of a few heads).