How to Install a Capacitor

Co-authored by Jason Shackelford

Last Updated: April 2, 2024 References

If you are using large accessories such as an upgraded car stereo system, they can often put a strain on your electrical system. If you feel like other accessories are struggling to get the power they need or you notice your headlights significantly dimming, then it may be time to install a capacitor. A power capacitor is an extra accessory that you can use that acts as a power storage device to supplement the electrical capabilities of your vehicle. An auto mechanic can install a capacitor, but you may find the process easy enough to handle on your own.

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Part 1

Part 1 of 3:

Choosing a Capacitor

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The capacitor acts as a storage tank for electrical power. The amount of power that the capacitor can store is measured in Farads and the general rule of thumb is that you will need one Farad of capacitance for every one kilowatt (or 1,000 Watts) of power demand in your system.^{[1]
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Some capacitors come with built in meters that display their current charge. Keep in mind that if you go this route you will need to wire the meter into a switched power supply so that it the meter turns off with the car. Otherwise, the meter would stay on constantly and drain your system.^{[2]
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Odds are, if you need a capacitor, you have dropped some money on electrical components in your car. The cost of your capacitor could range from around $30.00 to over $200.00 depending on how large and how fancy you decide to go. Remember that they all serve essentially the same function, and that for most people a one Farad capacitor without an internal meter will work just fine.

Part 2

Part 2 of 3:

Installing a Capacitor

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A charged capacitor can release a large amount of energy very quickly. This can be quite dangerous. You should always handle electrical components with care. ^{[3]
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Disconnect the battery ground terminal. This will kill power electrical system and allow you to work safely.
- If you already have a capacitor in your system you will need to discharge it. Capacitors store power, and thus can still shock you even after removing the power supply.
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Mount your capacitor.The capacitor can go in a number of places in your system. There is only a negligible difference in effectiveness no matter where you place it, but nearest the components that are struggling to get power (such as dimming headlights) is considered best. It is important that wherever you place it has a suitable place to mount the capacitor away from passengers.
- Although you are installing the capacitor to keep up with the extra power that is being pulled from accessories such as an upgraded stereo system, you have to remember that the capacitor is like a storage tank for power that supplements the whole system. By putting it close to the parts that are not getting sufficient power you allow it to supply power to those parts with minimal loss do to the extra resistance of a long wire.
Whether you are connecting to the battery, amp, or a distribution block of some kind, you need to connect the positive terminal of the capacitor to the positive terminal of the other component by running a wire between them. Eight gauge wire is usually recommended.
This terminal needs to be connected to ground.^{[4]
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If your capacitor has an internal meter, it will also have a third wire. This is the remote turn on wire and serves to kill power to the meter whenever the car is turned off. You will need to wire this into the remote turn on wire into any 12 volt switched power source (such as the ignition switch or amplifier).^{[5]
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This will restore power to your system. All of your components should now be working.

Part 3

Part 3 of 3:

Charging a Capacitor

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This fuse is installed with your system to prevent damage to the electrical components of your car, but will need to be removed before charging the capacitor. It should be near the battery on the main power line for your audio system.^{[6]
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This will provide you with a place to install the resistor that will help you charge your capacitor. The resistor allows the capacitor to charge more slowly. This prevents damage to the capacitor and the electrical system.
It is usually recommended to use a resistor that is 1 Watt and 500-1,000 Ohms. A higher impedance (Ohm value) will charge the capacitor more slowly and prevent damage. Connect the positive terminal of the capacitor to the resistor.
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Measure the voltage on the capacitor with a voltmeter. A multi-meter will do the job fine as well. Set it to read DC Volts and put the positive lead of the meter on the positive terminal of the capacitor and the negative lead of the meter to ground. When the meter reads 11-12 volts, the capacitor is charged.
- Another way to charge a capacitor is to wire a test light from the positive terminal of the capacitor to the power line. As long as the capacitor is charging, there will be current flowing through the light and the light will shine. Once the capacitor is charged the light will go out because current will no longer be flowing (the voltage drop between the power line and the capacitor will be zero).
It is no longer necessary to monitor the status of the capacitor. If you used the light method, you can now remove the test light.
Disconnect the positive terminal of the capacitor from the resistor and disconnect the resistor from the power wire. It is no longer needed, so you can store it away in case you ever need to charge your capacitor again.
This will allow your audio system to receive power once again.

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Question

What do I do if there is no place on a capacitor for a remote wire hookup? Should it come on when the main fuse is put into place, and what would cause the capacitor to power up, but not the amp?

Community Answer

If there is absolutely no place to wire a remote turn on lead for a capacitor, it has a built in turn on/off function for the cap, which will turn on when you turn on the car and power up everything. If the amp is not turning on, do you have the power wire running from the (+) terminal of the cap to the Power input of the amp?

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Do I need to use a resistor to charge the capacitor, or can I just use the test light?

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You can use the test light, but be sure to connect the capacitor in series with the test light.

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If both the amp and cap have a remote wire, do I need to split and connect it to both?

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Yes. You will actually just run the remote turn on wire from the amp already hooked up, and then run the turn on to the cap.

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Tips

If you find the electrical problem persists even with the extra power from a capacitor, it may be time to upgrade your vehicle's alternator.

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Keep safety in mind when working with a charged capacitor. Wear safety glasses or goggles and remove any jewelry before installing the capacitor.

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Most capacitor models encompass a safety circuit which will light up a warning if the connections are not correct. If the light comes on, disconnect the capacitor and double-check your connections..

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Warnings

Never install an uncharged capacitor. It is an instant power draw on the system and will blow any fuse in the system. Always charge the capacitor first.

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Discharge the capacitor before disconnecting it from the circuit. Do this by connecting the resistor across the leads of the capacitor.

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Never hold a resistor in your hands when charging/discharging a capacitor. They can get very hot, and if you have chosen too small of a resistor, they can blow up.

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