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What You Should Know About Sizing Power Inverters

 Power = Volts x Amps. Power is Measured in Watts.

Click here if you missed Introduction to Choosing a Modified or Pure Inverter.

Part 3. Introduction to Inverter Power

Since Inverters are sized by their Power Rating, we need to get a little technical again, but as before, we will try to keep it short and sweet and again, most will be able to follow along, but you can scroll down the page to Part 4. "Choosing the Inverter size" if you choose to.

Lets go over a few terms first. You do not need to completely understand these, but a little familiarity will be helpful.

  • Voltage - Think of Voltage as a force or pressure that pushes electricity through a wire. The higher the Voltage, the more force that is applied. There are 2 flavors of Voltage. DC and AC.

    • DC Voltage - A flat steady rate voltage like the voltage your vehicle's battery provides. (Left side of image below)

    • AC Voltage - A varying voltage, that alternates or cycles between a positive value and a negative value. The most common being the sine wave. (Right side of the image below). There are 2 important components of AC Voltage. Peak and RMS.
      • Peak Voltage - The highest voltage an AC voltage reaches during it's cycle. For household 120 Volts it is about 170 Volts.

      • RMS Voltage - Think of RMS as a sort of average voltage, that is equivalent to the same DC voltage. For household the RMS Voltage is about 120 Volts. It would take about 120 DC Volts to supply the same force to the circuit.

  • Amps - Think of amps as the electricity that is being pushed through the wire.

  • Resistance - Think of Resistance as the force that pushed back on, or resist the amps that Voltage is pushing through the wire.

    Note: The smaller the wire size, the more resistance it has, therefore the more heat that is created. The more amps moving through a wire, the more heat that is created. The more heat created, the larger the wire needs to be, to prevent heat from burning up the wire.

  • Power - Power is equal to Volts multiplied by Amps. Sometimes referred to as VA where V = Voltage and A = Amps. Power is measured in Watts. A "K" is used for Kilo or 1,000, so a 5KW Inverter would mean that the Inverter can handle 5 Kilo Watts or 5,000 Watts.

    Note: Since Power is Volts x Amps, the higher the voltage is, the less amps. The lower the voltage is, the higher the amps. The higher the amps, the larger the wire needs to be to control heat and prevent the wire from burning up.

    Example: A 12 Volt 1,000 watt Inverter has a 12 Volt DC Input and a 120 Volt AC Output. Therefore since Power = V x A, we find Amps by dividing Power by Voltage. On the 12 Volt input side, we have 1,000/12 = 83.3 Amps. On the 120 Volt AC output side we have 1,000/120 = 8.3 Amps. It should be clear that the wiring on the 12 Volt side needs to be significantly larger than the 120 Volt side.

DC Voltage and AC Voltage

Once you have determined the Amperage of each side of an Inverter, you can figure out the wiring size needed for the DC side and the amount of load you can use on the AC Side. There is literally no difference in sizing a 12 Volt DC wire for a 12 volt DC system and sizing a 120 volt AC device to a 120 volt AC system.

Part 4. Choosing the Inverter Size

To select the right Inverter size, you will need to estimate the total load you will be using. Following are instruction to size the right Inverter for your needs.

  1. Make a list of all of the appliances, equipment and tools, that you can think of, that you might use now and in the future.

  2. Next to each device put the Power, that it will draw. See the top 2 Wattage Charts, Appliance Power Charts for Sizing Inverters for help.

  3. Think about which appliances you will need to use at the same time and add up their Power in Watts. Do not add all the appliances on your list. What you are looking for is the maximum amount of power you will need at any time.

    Example, if you have the following on your list: a drill 25w, a cordless saw 35w, a microwave 1,100w and a 25"TV 220w, you should already know, that you will need an Inverter for at least the 1,100w Microwave, but you also need to think about what you might be running with the Microwave running at the same time. You could have the TV on and you might also be using the Drill while waiting for your food to heat up, but you would not be using the Drill and the Saw at the same time, so you would not add both the saw and the drill watts, but instead only add the one with the highest rating. 1,000w + 220w + 35w = 1,255w of power your Inverter will need to supply.

  4. Multiply the total watts by 1 1/2 times to account for future growth and as a safety factor. In our example, that would make it a total of 1,882.5w.

  5. Choose the next size up Inverter. In our example, you would probably want a 2,000w Inverter. You could probably get by with only a 1,500w, especially if you decide to only use the microwave by itself.

    Note: Inverters draw power, even when not in use. Notice when you hook an Inverter to a battery, you get a spark. Because of this, RoadTrucker recommends, that for Inverters 1,000 watts and greater, you also buy a remote switch to turn your Inverter off when not in use. The switch is cheap and RoadTrucker makes it very easy to get the correct Remote Switch when you purchase your Inverter with us. You will see a checkbox just above the "Add to Cart" button for each Inverter. Just check it and the proper Remote Switch will be added to the shopping cart, along with your Inverter.

    If you already have your Inverter, then find your Inverter on RoadTrucker's Inverter page, check the box to add the Remote Switch and change the 1 to 0 to remove the Inverter before clicking the "Add to Cart" button. You can also remove the Inverter once in the Cart.

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