Whether you want to rock on the go or just want to play outdoors for a while, running a guitar amplifier off of a car battery isn’t difficult or too expensive. All you really need is to convert the DC power from your vehicle into AC, which is the kind that comes from your wall. Most car batteries are strong enough to power a 50- or even a 100-watt amplifier, though you will drain your car battery after a bit.
Figure out how much electrical current your guitar amplifier draws from a normal wall socket. When you plug your amplifier into the wall, depending on how loud or how many instruments you are powering with it, the amplifier will draw a different amount of electrical current depending on the usage. Each amp is different and can draw from 40 watts--less than a kitchen light bulb--to 1500 watts, which is as much as large appliances like washing machines. Watts are the unit of measurement used to calculate electrical power. You can find how much the amplifier will use--or the amount of watts it will use at 100 percent usage when plugged in--somewhere on the identification plate or in the user’s manual. Many 40-watt amps will draw up to about 150 watts from the power supply.
Take the electrical current, or the watts your amplifier uses at 100 percent, and add about 25 percent more to it to make sure you don’t blow or short any fuses on your amplifier or car. So for a 40-watt amplifier that draws 150 watts from the power supply, you can figure about 180 watts of overall power.
Calculate the amount of amps your amplifier will draw off the power supply with the following equation: Amps=Watts/Volts. So for the 40-watt amp drawing 180 watts from the power supply at the standard 110 volts AC--which is what comes out of a wall socket in the U.S. (220 volts for Europe and Asia)--your maximum load current will be about 1.6 amps of power. Again, to be safe, you should add a little extra and estimate the output around 2 amps of power. Basically, amps are the unit used to measure current, so this number is the amount of current output from your guitar amplifier running at 100 percent and adding a bit more for safety. Remember, watts are the overall electrical measurement for electrical power, and amps are the measurement of current from the power supply, or how much power comes out at once. These are two different things.
Buy either a modified sine wave converter or a pure sine wave converter. These can be purchased at most auto accessories stores and will convert your DC car battery into AC power, so you can plug almost any AC appliance into the sine wave converter. Make sure you buy a sine wave converter with an output capacity that’s higher than the number you found in Step 3.
Plug the sine wave converter into the cigarette lighter, or if it has red and black cables, connect them to your car’s battery. Then plug the amplifier into the converter, and you should be ready to play.
Working around high voltage from a wall, car or amplifier is potentially lethal, so follow the steps above and do not try to disassemble any amplifier parts.
Using the amplifier with your car off will drain your battery.