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# Running a Power Inverter on a Car Battery

How Long Will Your Power Inverter Last You?

Power inverters are great tools that take a direct current (DC) and turn it into a conventional alternate current (AC). Power inverters come in an assortment of various sizes and power output. When you’re shopping for one, it’s incredibly important that you know exactly what you’re going to be using it for. And often times, you’ll want to make sure you buy one that’s capable of outputting even more than that.

As an example, let’s say you want to purchase one for your home that will run your laptop (300 watts) and power some lights (120 watts). What you’ll be looking for is a power inverter that will be strong enough to power at least 420 watts. But you never know if you might want — or even need — to run more devices simultaneously. In this case, you’d be safe with purchasing a 500 watt power inverter, but you might want to look at 600 watts, just to be safe.

Once you’ve decided on the power output you would want, your next question might be in regards to how long a single charge will get you. The answer to that question can be a little involved depending on the voltage of your battery, how many amps per hour it’s rated, and the combined wattage of the appliances you plan to run. The last thing you want to do is completely drain your car battery!

Didn’t Think You’d be Using Math Did You?

So, let’s use our example from above in another example. Since DC batteries come in either 12-volt or 24-volt variants, let’s assume we have the former. Let’s also say that your 12-volt battery is rated at 50 amp hours. We know from before that our computer and lights are going to be 420 watts, so we’ve already done the math for that. Below is one equation we’ll want to use for this:

(10 x (Battery Capacity in Amp Hours) / (Load Power in Watts)) / 2 = Run Time in Hours

The formula above is used when you are running a 12-volt battery. I’ll post the 24-volt formula a little further below. Plugging the numbers into the equation, we get this:

(10 x (50) / (420)) / 2

This will give us the answer .59 hours, which we can convert into about thirty-five minutes. So, this means that if our battery is fully charged, we can power our computer and the two 60 watt lights for 35 minutes before we’ll have to recharge the battery.

The formula for a 24-volt battery is listed below:

(20 x (Battery Capacity in Amp Hours) / (Load Power in Watts)) / 2 = Run Time in Hours

If we plug in the same numbers, we get 1.17 hours, which is about an hour and ten minutes. So, as you can see, you’ll get roughly twice the battery life per charge when compared to a 12-volt battery.

Wrap Up

After seeing how much power is actually used while running your devices, it becomes a lot easier to see how important each spec comes into play when deciding what to buy. You can use these calculations not only to get a good estimate on how long your battery will last, but also when determining what specs are going to get you the furthest for your money. Read our Buying Guide to learn all about the different models and wattage available.