How to charge a Capacitor

The capacitor or cap is one of the most overlooked accessories in car audio. They can help make the difference in about any size stereo system regardless of the total wattage. A cap is basically an energy storage device similar to a battery; however there are key differences between a battery and a cap.

A cap will store energy similar to a battery but a capacitor can actually discharge large amounts of energy very quickly.  A battery is designed to hold a large amount of energy and discharge that energy over a long period of time. A capacitor will always be charging when there is an extra load of current running through your electrical system. There is always wasted energy just waiting to be used, so the cap will harness this energy and store it for later use. Then for instance, if you’re playing your system continuously and your amplifier suddenly hits a very low bass note there may not be enough voltage to go around. Your capacitor will use that extra energy and give your amp a much needed boost of power. This boost balances your system out and will keep a more stable electrical load on your vehicle. A cap in simple terms opposes any change in voltage. That's why it helps keep your headlights from dimming or causing many other serious electrical problems from happening in the first place. Another general rule for car audio is for every 1000 watts of power that your system is capable of producing; you should have 1 farad of protection.

Now that was have a basic understanding of the car audio capacitor and its functions lets take a look at the process for connecting a capacitor. There are a vast variety of capacitor brands and farad ratings to choose from. So where to start? Well when choosing a cap there are going to be several factors to choose which cap will work best for your application. Let’s look at an install that would be ideal for adding a capacitor. First the equipment being run in this example is a 500 watt subwoofer amplifier. This amplifier has the ability to produce up to 1000 watts so in this case I recommend at least a 1 farad capacitor to cover this system. The vehicle already has a 4 gauge wire being used for power and ground connections. For this install we decided to use a Stinger 1 farad cap. To add the cap to this system we are going to need are some 4 gauge ring terminals, and additional power wire and ground wire.

(Step 1) First to start we remove the fuse up at the fuse holder near the battery. From there we can safely disconnect the main power wire connection at the amplifier

(Step 2) Add a ring terminal to your main power wire coming to the back of the vehicle from the battery, instead of going directly to amp it now goes into the capacitor. Also depending on where you’re planning to install the cap relative to your amplifier you will need some wire to run the short distance between two. If mounting the cap right next to your amp for instance 2 or 3 feet should be plenty of wire.

(Step 3) Connect another ring terminal to the short wire and the other end connects direct into your amplifier. Loosely tighten the Allen terminal on the positive side of the capacitor for now.

(Step 4) As far as the ground which is currently connected to your amplifier, disconnect it from the amplifier run it directly to the capacitor, add another ring terminal at this point and connect to the cap.

(Step 5) Now the last step is we need another short ground wire to run from the cap to your amplifier. Use another ring terminal and connect it to one side of the short wire and connect this at the ground on the cap, from there the other short end runs into your amplifier.

(Step 6) The final and last step is charging the capacitor; this is generally the part most people get confused with. The capacitor will include a resistor, which basically looks like a small light bulb. To charge the cap, remove the loosely connected Allen screw on the positive side of the cap, this is where the main battery lead and the lead running into your amplifier should be temporarily connected. Move the lead connecting to the amp off to the side from now, connect one end of the resistor to positive terminal on the cap and screw down the Allen terminal just to hold in place temporarily.

 Now, very carefully connect the other end of the resistor to your main battery lead, no worries yet since the fuse is still removed. It helps if you have a friend hold the main battery lead while doing this, reconnect your main fuse and hold the ring terminal to the resistor and the cap will start to charge……

If the cap has a digital voltage meter you will see voltage slowly start to climb. At first the resistor bulb will be very bright and slowly start to dim. Once the bulb is completely dim the cap is charged.

Remove your main fuse one more time and carefully reconnect your positive ring terminals for the battery lead and the amp lead, it’s okay if you have a small spark, this is normal.

After that tighten and check all connections and put the fuse back in. Test your amplifier and reset your amp and deck settings if needed. It’s normal for the cap to remain on for up to about 4 or 5 minutes after the car has turned off, it actually recharges itself and will turn on and off automatically as needed. One last thing I want to mention is you ever need to disconnect the cap and store it. The cap will still hold a charge even if it is disconnected from the vehicle so you will also want to discharge it after you are finished using it. To discharge it: connect the resistor between the positive and negative post on the cap. The resistor bulb will be bright at first and slowly dim out. Once it is completely dim the cap is discharged and safe to store.

Below is also a typical wire diagram for connecting a capacitor so you can reference my notes above.

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1 Farad Capacitors - 2 Farad Capacitors (and higher) - Hybrid Capacitors

Popular capacitor brands include:

Stinger Capacitors - Sound Quest Capacitors - Power Acoustik Capacitors