check if cap is working properly
04-15-2002, 12:15 AM
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check if cap is working properly
how can i check my 1 farad cap is working properly during playing? should i just use a multimeter and see if there is volts passing through while the system is playing? cause i noticed that my headlights dim when when the base hits. i have a rf punch 500X and a rf punch 400.4 amp. the 500X is the sub amp. the cap is hooked up before that amp. why is it still dimming? do i need for capacitance?
04-15-2002, 12:46 PM
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caps don't really do much for your car,,, i think the best thing todo if u have the money is to upgrade the alt... cause i have tested caps and the volts still drop when the bass hits... alot of ppl say its not worth it and just deal with the slight dimm... either that or turn it down a little... lol 
...
...
04-15-2002, 08:32 PM
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04-18-2002, 04:23 AM
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Caps...
I don't have any experience with super high powered car audio systems. BUT a cap doesn't provide power, it simply stores it. What it provides you is a little bit of storage so that the power supply doesn't sag momentarily. If you put a prolonged current draw on ANY power supply it will sag at some point.
In the case of adding a Capacitor across your battery, you are only adding a few milliseconds of storage before the capacitor will drain down to the level of the lowest SOURCE of power in your system. In a car electrical system, The alternator does supply the highest level of voltage. It does this in order to keep the battery charged. The battery by itself DOES SOURCE power. It is typically somewhere around 12.6volts. The alternator/rectifier and voltage regulator typically put out about 13.8volts. You can measure this with a voltmeter across your battery. It will be around 12.6 volts before you start your car and run up to around 13.8 volts with the engine/alternator running. The alternator has a limit as to how many amps of current it can supply before it falls down to the level of the battery, which in turn has a limit of how much current it can supply rated in amp/hrs.
A simple Cap tied across all of this power can only help to hold up the voltage MOMENTARILY when an excessive current draw on the system would otherwise sag the alternator and battery voltage.
Don't expect miracles from a cap. It is useful to filter out alternator whine more than anything else. There is a simple time constant involved with the charge and discharge time of a capacitor. One time canstant is equal to the capacitance in farads times the resistance in ohms. One time constant will charge a cap to approximately 63.2% of its value, two time constants will charge it to approximately 86.5%, and three time constants equal 95%. It is an exponential charge and has to do with the natural logarithm of nature. It is theoritically impossible to completly charge the cap to 100%. 99.999999999999..... is what actually happens. MORE IMPORTANTLY. The discharge of a cap is just the inverse of this. One time constant will discharge the cap down to 36.8% of its original fully charged value. Two time constants will drain it down to 13.5% of the original value and three time constants will have it down to 5% of its value, and so on.
For explanation purposes, Let's say for example you have a current draw on a 14volt system which is pulling 50 amps. Ohms law tells you that the resistance of that circuit is 14 (volts) divided by 50 (amps) equals .28 (ohms). That means that the power supply voltage source is looking at a .28 ohm load! With even a giant 1 farad cap, the time constant of 1 times .28 says that the voltage would be drained down to 36.8% of its original 14volt value, or 5.15 volts in only .28 seconds (280 milliseconds). Obviously the power amp would shut down way before 5 volts and the battery would be what was continuing to supply power long before that point anyway. The battery would be taking over as soon as the rest of the supply fell to around 12volts.
I could post the universal time constant formula, but it's too hard without the proper text font here. SO let's just say that the cap is only important as long as it holds up the charge between 12 and 14 volts. Once the cap drain falls below 12 volts, you are going to see your lights dim, etc. and it will be the battery doing all the work at that point anyway, NOT the cap. I've done the math, and for the cap voltage to drop down to say 82% of its full value, which would be down to 11.5 volts from 14 volts.... IT WOULD ONLY TAKE 2/10THS OF A TIME CONSTANT! .2 OF .28 seconds is only .056 seconds or 56 milliseconds! That's enough time to only sustain one cycle of full voltage at 17.86 hertz!
BOTTOM LINE... A 1 FARAD CAP WILL ONLY HOLD UP YOUR SUPPLY VOLTAGE FOR ONE CYCLE OF AN 18HZ NOTE, OR 56 MILLISECONDS with a current draw of 50 amps.
Just the facts... If you're experiencing your lights dimming due to an excessive current draw from your stereo amp. Don't look for caps as a miracle solution. You could add ten of these monsters, and you'd still only have enough reserve to keep you up for about a half of a second (560 milliseconds). IF you've got a sustained bass note longer than that, you'd still be in trouble. And you'd also have to have a period of little or no current draw to allow the cap to charge back up in time for the next heavy note to hit... If you are in a constant bass situation that is continuously pulling more current than the alternator can supply, then the cap would only help you out for the first 56 milliseconds, and then it would never be allowed to charge back up until the heavy current draw went away and the alternator again started increasing the voltage to again charge the cap.
You've either got some copper losses in the form of resistance in the wiring or wiring crimps somewhere that are acting like big resistors during this period which is dropping the voltage to your amp/speakers. If your system is pulling 50 amps, it would only take a resistance of .04 ohms to drop 2 volts off of your voltage power source. However, this wouldn't account for the lights dimming unless the wiring resistance problem is between the alternator and battery or somewhere else in series with the lights, before going off to feed the stereo. You might want to re-think the point where ever you tapped off the power from to feed your amp... If there is no wiring resistance problem, then you are most certainly loading the alternator more than it can handle.
Like I said, I haven't worked with these high powered car audio systems. I personally don't need that kind of ground moving bass. But to each his own... I am, however, an engineer who used to design professional audio amplifiers for stadium use, etc. I'm just trying to help, even though I have no intention of modifying my system to the extent that it needs a bigger alternator or battery or gigantic sized caps and double aught wiring... just to keep the lights from dimming. I guess I must be getting old...
fgf Yet, I hope some of this has helped to clarify some physics to some of you...
In the case of adding a Capacitor across your battery, you are only adding a few milliseconds of storage before the capacitor will drain down to the level of the lowest SOURCE of power in your system. In a car electrical system, The alternator does supply the highest level of voltage. It does this in order to keep the battery charged. The battery by itself DOES SOURCE power. It is typically somewhere around 12.6volts. The alternator/rectifier and voltage regulator typically put out about 13.8volts. You can measure this with a voltmeter across your battery. It will be around 12.6 volts before you start your car and run up to around 13.8 volts with the engine/alternator running. The alternator has a limit as to how many amps of current it can supply before it falls down to the level of the battery, which in turn has a limit of how much current it can supply rated in amp/hrs.
A simple Cap tied across all of this power can only help to hold up the voltage MOMENTARILY when an excessive current draw on the system would otherwise sag the alternator and battery voltage.
Don't expect miracles from a cap. It is useful to filter out alternator whine more than anything else. There is a simple time constant involved with the charge and discharge time of a capacitor. One time canstant is equal to the capacitance in farads times the resistance in ohms. One time constant will charge a cap to approximately 63.2% of its value, two time constants will charge it to approximately 86.5%, and three time constants equal 95%. It is an exponential charge and has to do with the natural logarithm of nature. It is theoritically impossible to completly charge the cap to 100%. 99.999999999999..... is what actually happens. MORE IMPORTANTLY. The discharge of a cap is just the inverse of this. One time constant will discharge the cap down to 36.8% of its original fully charged value. Two time constants will drain it down to 13.5% of the original value and three time constants will have it down to 5% of its value, and so on.
For explanation purposes, Let's say for example you have a current draw on a 14volt system which is pulling 50 amps. Ohms law tells you that the resistance of that circuit is 14 (volts) divided by 50 (amps) equals .28 (ohms). That means that the power supply voltage source is looking at a .28 ohm load! With even a giant 1 farad cap, the time constant of 1 times .28 says that the voltage would be drained down to 36.8% of its original 14volt value, or 5.15 volts in only .28 seconds (280 milliseconds). Obviously the power amp would shut down way before 5 volts and the battery would be what was continuing to supply power long before that point anyway. The battery would be taking over as soon as the rest of the supply fell to around 12volts.
I could post the universal time constant formula, but it's too hard without the proper text font here. SO let's just say that the cap is only important as long as it holds up the charge between 12 and 14 volts. Once the cap drain falls below 12 volts, you are going to see your lights dim, etc. and it will be the battery doing all the work at that point anyway, NOT the cap. I've done the math, and for the cap voltage to drop down to say 82% of its full value, which would be down to 11.5 volts from 14 volts.... IT WOULD ONLY TAKE 2/10THS OF A TIME CONSTANT! .2 OF .28 seconds is only .056 seconds or 56 milliseconds! That's enough time to only sustain one cycle of full voltage at 17.86 hertz!
BOTTOM LINE... A 1 FARAD CAP WILL ONLY HOLD UP YOUR SUPPLY VOLTAGE FOR ONE CYCLE OF AN 18HZ NOTE, OR 56 MILLISECONDS with a current draw of 50 amps.
Just the facts... If you're experiencing your lights dimming due to an excessive current draw from your stereo amp. Don't look for caps as a miracle solution. You could add ten of these monsters, and you'd still only have enough reserve to keep you up for about a half of a second (560 milliseconds). IF you've got a sustained bass note longer than that, you'd still be in trouble. And you'd also have to have a period of little or no current draw to allow the cap to charge back up in time for the next heavy note to hit... If you are in a constant bass situation that is continuously pulling more current than the alternator can supply, then the cap would only help you out for the first 56 milliseconds, and then it would never be allowed to charge back up until the heavy current draw went away and the alternator again started increasing the voltage to again charge the cap.
You've either got some copper losses in the form of resistance in the wiring or wiring crimps somewhere that are acting like big resistors during this period which is dropping the voltage to your amp/speakers. If your system is pulling 50 amps, it would only take a resistance of .04 ohms to drop 2 volts off of your voltage power source. However, this wouldn't account for the lights dimming unless the wiring resistance problem is between the alternator and battery or somewhere else in series with the lights, before going off to feed the stereo. You might want to re-think the point where ever you tapped off the power from to feed your amp... If there is no wiring resistance problem, then you are most certainly loading the alternator more than it can handle.
Like I said, I haven't worked with these high powered car audio systems. I personally don't need that kind of ground moving bass. But to each his own... I am, however, an engineer who used to design professional audio amplifiers for stadium use, etc. I'm just trying to help, even though I have no intention of modifying my system to the extent that it needs a bigger alternator or battery or gigantic sized caps and double aught wiring... just to keep the lights from dimming. I guess I must be getting old...
fgf Yet, I hope some of this has helped to clarify some physics to some of you...
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