The last thing you want to do is set up your off-grid system only to find that your inverter isn’t powerful enough to run your trusty microwave.
All microwaves are different, but the average 1,000-watt microwave requires at least 1500W of power to run properly. To make sure you end up with the right inverter, let’s take a look at how to determine what size inverter you need to run a microwave. It’s quick, easy, and it’ll ensure you don’t waste your money.
At some point, many of us who enjoy off-grid living have asked, “What size inverter do I need to run a microwave?”
Fortunately, it’s incredibly easy to figure out what size and power sine wave inverter you need to run a microwave. Naturally, you’ll start by taking a look at the microwave itself.
The first thing you’ll need to figure out is how many watts the microwave uses while running, which is usually as easy as finding where it’s noted. This can be on:
If you’re unable to find it after looking in all of these places, you can get a pretty good idea using the USDA recommended method – “Time-to-Boil Test.” Here’s how to do it:
If the water boils in less than two minutes, you have a 1000 watts microwave. If it took around 3-4 minutes for the water to boil, you have a slow oven. (1).
If the water boils in 3 minutes = average wattage oven (650 – 700 watts or more)
Now you should have a pretty good idea of your microwave’s continuous wattage rating. Note that, this refers to the ‘cooking power’ of the microwave (as we explain below). Hence, there are other factors to keep in mind when answering the question “What size inverter do I need to run a microwave?”
When choosing an inverter, your microwave’s actual power consumption is what matters, and not the cooking power.
It’s important to note that a microwave’s cooking wattage is lower than the wattage it consumes, so take that into account when choosing an inverter size. This is often referred to as ‘Input Wattage’ (for actual power consumption), and ‘Output Wattage’ (for cooking power).
A microwave’s cooking wattage is lower than the wattage it consumes.
Most microwaves use energy with about 60-70% efficiency (2). So if you’re unable to find your microwave’s actual power consumption noted anywhere, you can use some simple math to figure it out.
Let’s assume a working efficiency of 65% for your microwave (on average).
Say you have a microwave that cooks at 700w. Let its actual power consumption be X.
X * 65/100 = 700W X = 700 * 100/65 X = 1076 ~ 1100W
That means your actual power consumption is around 1100W.
You can apply this technique to almost any microwave and estimate the actual power consumption, if you already know your cooking power.
Here’s a simple table that shows input power vs output power of common microwaves with 65% efficiency (3):
Interestingly, even though they require more power to run than they use to cook food, microwaves are still one of the more energy-efficient cooking methods, making them ideal for off-grid living. Scientific American states in a recent article (4):
Cooking or re-heating small portions of food in the microwave can save as much as 80 percent of the energy used to cook or warm them up in the oven.
That said, your microwave’s actual power consumption is what you need to worry about when choosing a sine wave inverter size, not the cooking power.
If you’re not able to determine your microwave’s wattage but know how many AMPS (current) it uses, there’s an easy conversion formula that will help you figure it out.
Just multiply the amperes by AC voltage, which is generally 110-120V for US citizens. The product is your wattage.
So if your microwave uses 12.5A of current, the formula would be: 12.5A * 120V = 1500W
Now that you know everything there is to know about determining your microwave’s continuous power usage, which is the power it consumes while running, it’s time to take a look at its peak wattage or the maximum amount of power it utilizes during a surge.
Peak wattage, or surge wattage, usually occurs during startup and lasts for less than a second, but your inverter needs to be able to handle this sudden surge in power. The process should look something like this:
Your microwave’s peak energy requirements should be listed on the owner’s manual or manufacturer’s website. If not, it’s a good idea to choose an inverter that can handle three to four times its continuous wattage just to be on the safe side.
As a reference, the surge power of a microwave can be as much as FOUR times the listed continuous power (so a 1000W microwave may have a peak rating of 4000W).
Ultimately, when you’re looking for sine wave inverters, you’ll notice on the specs sheet that both continuous and peak capability are listed, so it should be easy to tell if it’s large enough. To be on the safe side, you should have an inverter with a higher continuous/peak power rating than that of your microwave (by a factor of about 20%).
So, if all that was a bit too much for you to wrap your head around, don’t worry. We’ve wrapped it up in a few, simple steps:
We recommend getting a good pure sine wave inverter for this purpose, as it’ll maximize the power efficiency of your microwave, keep it running smoothly, and prevent any electrical malfunctions from occurring. For more tips to get the most out of your home’s appliances, check out our Homepage.
Yes, a 1500-watt power inverter should be able to run a 700-watt microwave without any issues. To be sure, check that the surge power rating of the microwave is also within the inverter’s limits. You can use a pure sine wave inverter or modified sine wave inverter, but the modified sine unit may cause your microwave to run less efficiently.
You can use a modified sine wave inverter or a pure sine wave inverter to run a microwave, as long as they have a large enough capacity, aka battery power. When you compare pure sine inverters vs modified sine inverters, modified sine models tend to shorten appliances’ lives, so that’s important to keep in mind. Pure sine wave inverters always offer better performance and efficiency, albeit at a higher cost.
Your inverter is big enough to run your microwave if it can handle its startup surge, and continuous wattage draw while it’s cooking. If your modified sine wave inverter or pure sine wave inverter can handle both successfully, you’re all set for your next road trip!
To help all this sink in, you can check out this guide that shows how to size an inverter to run a TV for a similar example.
Dara Brant is the Managing Editor at Green Building Elements. Prior to joining us she covered alternative energy news and local developments at Your Energy Blog. Dara has a passion for sustainable living and wants to do more than her fair share to help build a better tomorrow for future generations. You can connect with Dara on LinkedIn.
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