We decided to put together this tech tip on how to size a battery bank for an AIMS Power inverter because one of our biggest resellers, TheInverterStore.com, has a sale on batteries!

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Once you have all those batteries, you might need to know how to connect them … click ‘continue reading’ below for a full write-up and video on the subject!

First things first: How much power or watts are needed to run the desired appliances? You can find the max continuous output of your appliance in the user’s manual and sometimes on the product itself.

EXAMPLE: A Dewalt chop saw shows that it uses 15 amps AC under max load in the manufacturer’s user manual.

In order to figure out how much wattage that saw uses, multiply the 15 amps by 120 volts (the standard power system in America). This applies Ohm’s Law, which is Wattage = Volts X Amps (W=VA).

So 120 volts X 15 amps = 1800 watts of maximum output for the chop saw

Now before sizing the battery bank, make sure you find the proper power inverter that can handle that wattage output. An inverter will transform the DC electricity, stored by batteries, into AC power that can be used to run your saw, TV or any number of appliances.

A 2500 watt power inverter is a safe bet for this chop saw application.

REMEMBER: Now that we have our wattage output and inverter chosen, the DC amp output must be figured out in order to run the tool off a battery bank system.

So if using 12 volt batteries for the system, divide the tool’s wattage output by 12 volts in order to figure out how many DC amps are needed to run the tool.

W/V=A

1800 watts/12 volts = 150 amps DC

IMPORTANT: Now you know that 150 amps of DC power will run 1800 watts for about one hour. HOWEVER, discharging your batteries below 50 percent of the reserve capacity, will dramatically reduce the lifespan, limiting the amount of cycles the batteries can handle, therefore costing you more money in the long run.

So by multiplying the DC amps needed (150) by two, you help prevent the batteries from depleting below 50 percent charge. This will allow you to use and recharge the same batteries for six years or more, dramatically reducing costs. It’s always a good measure to double the size of your battery bank in order to extend the life of expensive batteries.

150 amps DC X 2 = 300 amp hour battery bank

You must also account for a standard 10 percent efficiency loss from the power inverter.

300 X .10 = 30 AND 300 + 30 = 330 amp hour battery bank.

However, in order to run a 15 amp, Dewalt chop saw for one hour, you’d be fine using three 100 amp hour batteries in parallel unless you plan on holding down the trigger for the whole hour. Accounting for the 10 percent efficiency loss of the inverter is more applicable if running something non-stop, such as a refrigerator.

In the video below, I used two 100 amp hour batteries to demonstrate the concept. With this battery bank, you’d be able to power the saw for about 45 minutes of work if using your chop saw intermittently.