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-   -   1 Farad capacitors for car audio (http://www.diyaudio.com/forums/parts/2579-1-farad-capacitors-car-audio.html)

ssanmor 4th March 2002 09:52 AM

1 Farad capacitors for car audio
 
Hello all!
Does anyone know how to build a controller for a 1 Farad capacitor for CAR audio applications? I have the bare capacitors, but they must not be connected directly in parallel with the battery, because they have to be charged slowly to avoid a great current peak when it is discharged.
I have not been able to find any link to a circuit, although I did once.

Any help will be greatly appreciated.

Thanks!

leroy 4th March 2002 11:37 AM

Why don't you charge the capacitor(s) with a resistor in series and then connect them parallel with the car battery? (And remove the resistor). High currents should not be a problem since capacitors are designed for it, you only want to avoid arcing when connecting the capacitor for the first time.

ssanmor 4th March 2002 01:10 PM

Yes, I also had that idea, but isn't it dangerous to have the capacitor permanently connected to the battery? It will always be drawing some current, due to the losses, won't it?
Besides, commercial caps have a lot of circuitry on the top of the bare capacitor, although this can be only rubbish to impress the buyer who is going to pay 200$ for it.

Thanks, anyway.

leroy 4th March 2002 01:35 PM

I noticed the electronics on top of the capacitor too, often a LED-display indicating the supply voltage. I must say I don't know for sure if the circuit is just for voltage measurement.
Leaving the capacitor connected in parallel it only draws milliamps due to the internal leakage, this should not be a problem since the car battery itself has even a higher leakage current. You can add a high current slow blow fuse for in case of a short circuit.

Phloodpants 29th March 2002 07:52 PM

I like this method... connect the capacitor in series with a small 12v automotive lamp of some kind. (like a dashboard light)

The light will glow bright at first, then gradually dim down to nothing once the cap is charged! Now you can bypass the lamp. You could even rig up some kind of 555 timer circuit to switch a relay across the lamp, or maybe a comparator with a relay that kicks in when the cap's voltage is the same as the souce.

Shaun Perez 16th October 2002 12:40 AM

these circuits on the $200 caps are just protection circuits for reverse polarity hookup and i believe overvoltage with diagnostic leds to indicate the operating conditions of these circuits. The voltage is displayed on a digital readout so as to note weather or not the capacitor is of a high enough value so that the voltage at the amplifier does not drop with a loud volume strong bass note. My system doesnt use the diagnostic top and consists of a plain old capacitor that uses the lowest ESR(Equivelent Series Resistance) manufactured by lightining audio, Lightening Cap. There are a few important things when using a capacitor for this use, low series resistance, voltage rating, and capacitance. Capacitance is determined by the total wattage of the system I believe it is 1\2 Farad is good on systems 500 watts or less. so 250 watts would only need 1/4 farad. Professional auto sound systems leave this capacitor hooked up directly to the battery at all times, of course fused, and only need to use a series resistor of a value of 220 ohms 5 watt when the capacitor is either installed or uninstalled to charge the capacitor. This configuration is Good because the capacitor is essentaillty acting like a super fast releasing battery that is supposed to be located within 1 foot of the amplifier. Batteries are slow reacting when it comes to the pulsating demands of nearly all music amplifying equipment and the cap is super fast. Even if the battery was fast(they're not!) the length of the power cable to the amp would limit the speed and power capabilities of it unless it were only 1 foot. So that is the reasoning for the cap. Lightening audio includes the resistor as well as instructions on using the cap.

Shaun Perez 16th October 2002 12:48 AM

these circuits on the $200 caps are just protection circuits for reverse polarity hookup and i believe overvoltage with diagnostic leds to indicate the operating conditions of these circuits. The voltage is displayed on a digital readout so as to note weather or not the capacitor is of a high enough value so that the voltage at the amplifier does not drop with a loud volume strong bass note. My system doesnt use the diagnostic top and consists of a plain old capacitor that uses the lowest ESR(Equivelent Series Resistance) manufactured by lightining audio, Lightening Cap. There are a few important things when using a capacitor for this use, low series resistance, voltage rating, and capacitance. Capacitance is determined by the total wattage of the system I believe it is 1\2 Farad is good on systems 500 watts or less. so 250 watts would only need 1/4 farad. Professional auto sound systems leave this capacitor hooked up directly to the battery at all times, of course fused, and only need to use a series resistor of a value of 220 ohms 5 watt when the capacitor is either installed or uninstalled to charge the capacitor. This configuration is Good because the capacitor is essentaillty acting like a super fast releasing battery that is supposed to be located within 1 foot of the amplifier. Batteries are slow reacting when it comes to the pulsating demands of nearly all music amplifying equipment and the cap is super fast. Even if the battery was fast(they're not!) the length of the power cable to the amp would limit the speed and power capabilities of it unless it were only 1 foot. So that is the reasoning for the cap. Lightening audio includes the resistor as well as instructions on using the cap.

Circlotron 16th October 2002 02:23 AM

Quote:

Originally posted by Shaun Perez
This configuration is Good because the capacitor is essentaillty acting like a super fast releasing battery that is supposed to be located within 1 foot of the amplifier. Batteries are slow reacting when it comes to the pulsating demands of nearly all music amplifying equipment and the cap is super fast.
I read somewhere that the internal resistance of a car battery in *good* condition and no too old is approximately 10 milliohms. Draw 100 amps from it and the voltage at the terminals drops about 1 volt. That is the case at DC and very low frequencies to perhaps several Hz but I wonder what the internal resistance is like at high frequencies? A cap would definitely be a big help.

GP.

anothernewbie 16th October 2002 02:56 AM

Exactly. ever see the headlights dimming on those idiots driving around town booming all night long? Scary what those poor saps are doing to their alternators and batteries.

In my system, I'm using a 2F cap, and have ZERO problems. Total system power is around 2600W RMS with 3dB headroom... not exactly a small system. running 2/0awg battery cable, and I'm having no problems with mine.

a 220ohm resistor will take DAYS to charge a cap up to full voltage. try 10-20 ohms.. at 12V battery voltage, the current is ~1A. it'll still take close to a minute to charge the cap. ought to be sufficiently long not to hurt anything.. (Now take the cap off and short a wrench across the terminals... You have a welder for $100!!)

Personally, I wouldn't waste my time on spending the extra money on the ones with the digital readout. It's simply a gimmick to make people pay more for it. They charge another $100 for a volt meter stuck to the top of the same cap. You can make one for $15- or less when you make them by the zillion like the car audio companies.

Circlotron 16th October 2002 07:54 AM

1 Farad? Hah! Kids stuff.
 
I read that Epcos make a 2.7 volt 2700 Farad cap that when strung together in series is enough to start your car! That would be the ultimate! They are called Ultracaps.

GP.


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