How do you pre-charge a farad cap?

[Big House]

I am installing a new amp and need assistance in precharging my farad cap. I read this needs to be done, so I need to know how. Any help is appreciated.

[Black_Noise]

when i had one, it came with this little circut board that connected to the pos and neg of the capacitor, and then a pos and neg wire to hook up to a pos and neg source.


someone might chime in with more exact answer on HOW to do it.

[NATEHAWK]

hey bro all you need to do is hook it to the battery it will charge it up. the cap should have cam with a lil board that you hook the cap to then to the battery. Here you go man look at the bottom diagram

http://www.caraudiohelp.com/car_audio_capacitor_installati on/car_audio_capacitor_installati on.htm

[Big House]

Just following directions from that site you mentioned. I get how to wire it but the said something about pre-charging it before hooking it up to a 12V source so that the difference between the Cap and the battery is near zero.

[GreekGod]

NOTE OF CAUTION: Power capacitors store a large amount of energy and they charge very quickly. You must first "charge" your power capacitor using a resistor before connecting it directly to +12 volts. This is done with the a 1k ohm resistor and a voltmeter. The exact value of the resistor is not critical but I would keep it in the 500-1k ohm range. I would recommend getting a 1 watt resistor if possible (your capacitor may have come with a resistor for charging). A lower wattage resistor will heat up too quickly. Also, do not hold the resistor with your bare hand. The current flowing through the resistor will cause the resistor to heat up and you could be burned. A good place to put the resistor is in the main power wire fuse holder. Simply substitute the resistor for the fuse. A diagram for the capacitor charging setup is shown below. You will need to place a voltmeter across the capacitor to monitor the voltage. Once the voltmeter reads 12 volts you can remove the voltmeter and replace the resistor with the power fuse.

Alternatively you can measure the voltage across the charging resistor. It should start around 12 volts and slowly work its way down to 0 volts. When the voltage stops changing you have charged the capacitor completely.

http://www.caraudiohelp.com/images/car_audio_capacitor_charging.g if

[magindat]

Dale's pic is perfect.

You can use a 12v light bulb as the resistor.

Charge slow - not instantly.

[Pops]

The light bulb is what we use. Install the cap and leave the fuse out under the hood and then charge and install the fuse the fuse afterwords.

[O's Fan Rich]

what do these things do?
The name makes me think of a new Middle East Hat....

[RR|Suki]

what do these things do?
The name makes me think of a new Middle East Hat....

As I understand it the cap. keeps a "reserve" so that when your amp draws power you don't get that dimming effect, and don't prematurely wear out your batt.

[Joe Walsh]

DON'T PUT YOUR TONGUE ON THE + & - Posts!!!!

(Or YOU will sound like a subwoofer!)

:eek:

Yep, Those BIG Capacitors store 12V energy to help supply enough juice for those MONSTER speakers.
Especially when you have the stereo set at "11"....:)

[DOOM]

Whats up BIGHOUSE

[magindat]

The light bulb is what we use. Install the cap and leave the fuse out under the hood and then charge and install the fuse the fuse afterwords.

That's exactly what I do. I do the whole install without the fuse in place. Then I put a light bulb across the fuse holder and let the cap charge. It's bright when you start and fades as the cap charges. Then put the fuse in place and you're good to go.

[Zack]

Do those caps ever need to be recharged?

[Pops]

Do those caps ever need to be recharged?

Only if it were fully discharged Zack. The caps are used for the bass amp.

[magindat]

Do those caps ever need to be recharged?

Caps are interesting. They will hold charge, but not much amp hours. A lead acid battery holds charge by chemical reaction. A cap holds charge by storing electrons in an electrolytic gel.

the idea is superfast super high amperage discharge and superfast 'recharge'. This discharge/recharge cycle speed helps provide an amplifier with the amperage it needs right away for a musical transient (big boom) and then recharges what it lost almost instantly.

Caps don't like to go to or from absolute 0 quickly. The gel gets hot and expands. That's why the initial charge is to be slow. The cycle is only a volt or two when in service in a car.

Caps discharge so fast, they'll actuall explode the thing that contacted the posts. Like you can weld with a car battery - imagine all the welding energy stored in a car battery discharging instanty. Make big boom and big mess. So, we handle and store caps 'empty'. It takes a few minutes to charge through a light bulb and only a few moments to discharge through the same light bulb.

In an install, they are parallel to the battery, so never need 'recharging'. however, when working with the car battery on a capacitor equipped car, one MUST be mindful that the cap's energy is still avaialble on that positive terminal! If it touched a ground source - ouch! I've seen a flopping battery terminal touch the AC hose auliminum section, spark and blow a hole in the aluminum tubing!

Does this help, Zack?

[O's Fan Rich]

these things sound dangerous...
at what level of audiophiling do the become a necessary thing?

[Joe Walsh]

these things sound dangerous...
at what level of audiophiling do the become a necessary thing?

Usually the cars that have more subwoofers than cylinders...:P

[Pops]

Usually the cars that have more subwoofers than cylinders...:P


Right as usual Joe!!!!!!!!!! :D

[Joe Walsh]

Do they 'turbo' their alternator and 'VTEC' their voltage regulator??

They need 'NOS' just to run the electrical system load!

:lol:

[Pops]

The smart ones upgrade the alternater and add a second battery.

[Hotrauder]

I have full glass coverage so if it had anything to do with music I would be tempted...Dennis:P

[BAD MERC]

Here's the best way - leave the useless thing out. I one-farad cap will make ZERO difference. They store voltage and stabilize the line. They do not store amperage. Add a second battery - then we're talking.

[illwood]

Here's the best way - leave the useless thing out. I one-farad cap will make ZERO difference. They store voltage and stabilize the line. They do not store amperage. Add a second battery - then we're talking.

I half agree / half disagree with this statement, it depends on why a capacitor is being used.

The capacitor is properly used in audio systems to provide a power buffer during those occasional large bass hits (the reason I said bass is because due to the geometry of the sub, more energy is required to move it) that may dim your lights slightly and these short duration high draw situations are bad for the battery.

Capacitors used improperly when they are a band-aid to run larger power amps than your electrical system (alternator/battery) can handle.

In the first situation, a second batter would work, but a capacitor is smaller and easier to mount.

[magindat]

Here's the best way - leave the useless thing out. I one-farad cap will make ZERO difference. They store voltage and stabilize the line. They do not store amperage. Add a second battery - then we're talking.

They stabilize the voltage by storing amperage. It all boils down to WATTS (not Dennis) in the end. The cap dumps amps to the amplifiers on transient draw thus buffering the voltage drop and helping to prevent such things as dimming headlights. W=V*A

The old rule of thumb is 1 farad up to 1000W, 2 up to 2000, etc. I say put one in up to 1000W. After that, extra battery PLUS lots of capacitance. I once put a 50 farad on 8000W with a 250 amp alternator and a remote Optima. It did NOT dim the headlights at all!

Keep in mind also, that an extra battery is seen by the alternator as a LOAD. A cap is not seen by the alternator as a load due to the speed of charge/discharge. If you have reached the point of extra battery, a high output alternator is in order.

As far as the above comment about turbo-ing sound and stuff...
Think of high power amplifiers as a high HP motor. Without the fuel system to support it, it's a complete waste. All this alternator, battery and cap stuff IS that fuel system!

[Pops]

They stabilize the voltage by storing amperage. It all boils down to WATTS (not Dennis) in the end. The cap dumps amps to the amplifiers on transient draw thus buffering the voltage drop and helping to prevent such things as dimming headlights. W=V*A

The old rule of thumb is 1 farad up to 1000W, 2 up to 2000, etc. I say put one in up to 1000W. After that, extra battery PLUS lots of capacitance. I once put a 50 farad on 8000W with a 250 amp alternator and a remote Optima. It did NOT dim the headlights at all!

Keep in mind also, that an extra battery is seen by the alternator as a LOAD. A cap is not seen by the alternator as a load due to the speed of charge/discharge. If you have reached the point of extra battery, a high output alternator is in orde

As far as the above comment about turbo-ing sound and stuff...
Think of high power amplifiers as a high HP motor. Without the fuel system to support it, it's a complete waste. All this alternator, battery and cap stuff IS that fuel system!

Great way to put it all together Rich! You have to be able to keep the glass full!

[magindat]

I half agree / half disagree with this statement, it depends on why a capacitor is being used.

The capacitor is properly used in audio systems to provide a power buffer during those occasional large bass hits (the reason I said bass is because due to the geometry of the sub, more energy is required to move it) that may dim your lights slightly and these short duration high draw situations are bad for the battery.

Capacitors used improperly when they are a band-aid to run larger power amps than your electrical system (alternator/battery) can handle.

In the first situation, a second batter would work, but a capacitor is smaller and easier to mount.

It is true, they are not a fix, crutch or stop gap for a system which draws more than the alternator puts out.

Figure:
1000W/.80 (80% efficiency) = 1250W required
1250W/12.5V = 100Amps

This means your alternator should put out 100 amps at idle to support a 1000W amp. If your alt puts out 75 at idle, all the caps in the world aren't gonna magically create 25 missing amps!

BTW: Most class D amps today are about 85-90% efficient, but I took into account the notion that some of us 'old-schoolers' are running class B or B/C amps!

Also, in 20' of 0 guage, there is roughly .8 volts drop and in 4 guage, roughly 1.2 volts drop at 100 amps. Therefore, even though your voltmeter up front reads 13.5, the wire in the trunk will read about a volt LESS!

[Big House]

Not pushiung that much John, don't think I need an extra battery. The alternator charges well.


The smart ones upgrade the alternater and add a second battery.

[n00bkiller944]

Caps are interesting. They will hold charge, but not much amp hours. A lead acid battery holds charge by chemical reaction. A cap holds charge by storing electrons in an electrolytic gel.

the idea is superfast super high amperage discharge and superfast 'recharge'. This discharge/recharge cycle speed helps provide an amplifier with the amperage it needs right away for a musical transient (big boom) and then recharges what it lost almost instantly.

Caps don't like to go to or from absolute 0 quickly. The gel gets hot and expands. That's why the initial charge is to be slow. The cycle is only a volt or two when in service in a car.

Caps discharge so fast, they'll actuall explode the thing that contacted the posts. Like you can weld with a car battery - imagine all the welding energy stored in a car battery discharging instanty. Make big boom and big mess. So, we handle and store caps 'empty'. It takes a few minutes to charge through a light bulb and only a few moments to discharge through the same light bulb.

In an install, they are parallel to the battery, so never need 'recharging'. however, when working with the car battery on a capacitor equipped car, one MUST be mindful that the cap's energy is still avaialble on that positive terminal! If it touched a ground source - ouch! I've seen a flopping battery terminal touch the AC hose auliminum section, spark and blow a hole in the aluminum tubing!

Does this help, Zack?

Don't want to ask a dumb question here, but I had my cap installed by a friend who is in the audio business, but if I ever want to remove it how do i properly discharge it for safe storage?

Thanks

[Pops]

Don't want to ask a dumb question here, but I had my cap installed by a friend who is in the audio business, but if I ever want to remove it how do i properly discharge it for safe storage?

Thanks

The light bulb in reverse trick will burn the juice out of it. This is a wise move to make to keep them from grounding out!

[GreekGod]

My uncle taught me to discharge capacitors (in televisions & radios) by grounding a terminal of the "cap" to the chassis with an insulated screwdriver.

[n00bkiller944]

The light bulb in reverse trick will burn the juice out of it. This is a wise move to make to keep them from grounding out!

So just wait until the lightbulb no longer shines and then it is fully discharged?

[illwood]

So just wait until the lightbulb no longer shines and then it is fully discharged?

You can also use the multi-meter to see how close you are to zero volts (empty).

[Big House]

Man I really appreciate the help. Now if I had just read the contents on the package, it included the resistor for charging and discharging. But I am definitly smarter from the information shared here.