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For many off grid homes and RVers, a microwave is a must. It makes cooking and food preparation easy, but you have to make sure the inverter is the proper size. So is 1200 watts enough or do you need more?
A 1200W inverter can run a 600W microwave as it needs 1200 watts to start, but not a 700W model because it consumes 1400 watts. The watts labeled on a microwave refers to cooking power needs, but the startup power required might be 3 to 4 times the continuous watts.
Microwave Cooking Watts and Startup Watts Explained
There are many types of microwaves for RVs, but almost all advertise the cooking watts, not starting or surge watts. There is a big difference here.
If you see an 800W microwave, it means 800 watts are used to cook food. But the watts needed to start up the microwave is much higher, usually double or even more.
On paper, an 800W microwave seems like a perfect match for a 1200W inverter. But it is not, because the microwave requires 1600 watts for the initial surge.
If you have a 1200W inverter, the best option would be a 600W microwave as it probably needs 1200 watts at the initialization stage.
The larger the microwave the higher its surge watts will be. A 1500W model might need as much as 3000 or 5000 watts to turn on.
Some might argue that a 1200W inverter can handle a 700W microwave. If it only needs 1200 watts to start, yes it can. But most of these models need 1400 or even 1500 watts.
A high quality inverter might be able to handle 1400 watts, even if it is designed for just 1200 watts. After all it will be for less than a second.
But the problem is you will probably be using the microwave every day. Overloading an inverter will damage the system, so better get a smaller microwave or a larger inverter.
Read the Fine Print
If you check out inverter forums, you will see many complaints about their 1000 watt inverter unable to run a 700 watt microwave. Again this comes back to what we said about cooking and startup watts.
It is easy to assume that the inverter should be able to run the microwave. But the problem is not everyone knows the difference between cooking and powering up watt requirements.
It also does not help that microwaves rarely mention the startup power requirements. You might find this information hidden in the manual or specs sheet, so you have to be thorough.
If you want to be certain, check the microwave user manual or contact the manufacturer. If your RV is running on solar power, every watt counts. This applies for microwaves and every appliance you run.
Which Inverter is Best For Your Microwave?
There are two types of inverters, modified and pure sine wave. Which you choose will affect the microwave performance.
Pure sine wave inverters produce high end power similar to those used in homes. Power flows smoothly and appliances run as if on regular AC power. Our favorite is the GoWISE 1500W which can run a 700W microwave nicely.
Modified sine wave inverters are less expensive than pure sine. However the power does not flow as smoothly as pure sine wave.
In terms of quality, a pure sine wave inverter is the better option. Modern appliances run better with it, especially those with sensitive electronics. While it costs more you are assured of consistent results with your microwave.
But there are quality modified sine wave inverters available for appliances and even computers. If you can find a modified sine wave inverter that works with your microwave, it will definitely save you money.
If you are not sure what to buy, contact the inverter manufacturer. Ask them if their product is compatible with your microwave and any other appliance you will run on it.
Of course if money is not an issue, get a high quality pure sine wave inverter. You are assured the microwave and anything else you plug into it will run efficiently.
Is 1200 Watts Enough?
If you are going to use a 600 watt microwave, yes, it is enough. This is probably as far as how the inverter can go though.
But if you are going to use a 700W microwave or higher, get a large inverter. 1200 watts is just too small Some might say that you can overload inverters. That may be true but why risk it? This is crucial since this is an appliance you will use daily.
Microwaves are becoming more energy efficient, but 600 watts is probably the smallest you can get While the inverter itself can handle other appliances like lights, laptops, TVs etc. the powering up watt requirement of microwaves will push it to the limit.
How Many Batteries Do I Need?
Once you have decided what inverter to use, the next step is to find the right battery bank size.
In a solar system, the solar panels store DC power in the battery bank. The inverter converts DC to AC before it reaches the microwave. This is how it works regardless of the battery type.
A 600 watt microwave needs a 150ah 12V battery to run. 600 watts is equal to 50 amps, but the microwave needs 1200 startup watts or 100 amps. Lead acid batteries should not be drained beyond 50%, so a 150ah or 200ah battery bank is ideal. If you want to use a 150ah battery with your inverter, here is a guide.
While the microwave consumes 1200 watts at start, it is only for less than a second. After that its usage drops to 600 watts or 5 amps an hour.
Few people run a microwave for an hour, so its watt usage will be lower. If you use a 600W microwave for five minutes an hour, it consumes only 50 watts.
50 watts is 4.1 amps, so the microwave pulls 4 amps in 5 minutes. Run it for 10 minutes and that would be 8 amps.
Batteries discharge faster as more amps are drawn . So if the microwave uses 150 watts, it would pull 12.5 to 15 amps.
The basic calculations are simple:
volts x amps = watts
watts / volts = amps
watts / amps = volts
But there are several factors that affect battery performance. Its age, the weather, temperature, depth of discharge rate, load etc. may cause a battery to discharge at a faster rate.
How Solar Panels Help Run Your Microwave
With the right solar power system you can charge the battery bank to run the inverter. With sufficient power your microwave can run for as long as necessary.
Your microwave needs 1200 watts (100 amps) to start and 600 watts (5 amps) to cook. To be on the safe side you should have a 12V 200ah battery bank.
A 4 x 300 watt solar array can produce 100 amps in an hour, enough for the microwave. Once the appliance starts, you can use the battery to run it.
This solar array can recharge a 200ah battery bank in two hours. If you only use the microwave for a few minutes day, the solar panel can keep the battery bank and inverter going.
But this assumes you will only use the microwave for the battery bank. If you are going to use other appliances, it will require more solar panels and batteries. You will also need a bigger inverter.
The output of a solar array depends on several variables including the weather, the panel position, shading, efficiency rating and so on. This has to be accounted for as well as the inverter efficiency rating and that of the battery.
If a 4 x 300W solar array is too big for your RV, you can opt for 3 x 400W system which would provide the same results. For this tow work, make sure you have a large battery bank, an inverter and charge controller.
The battery charging time assumes you are only using the microwave. If you are going to run other appliances, the charge time will take longer. The weather, season and number of sun hours also play a role in deciding how long it takes to recharge the battery.
What is evident here is there are a lot of factors that should be addressed. From the microwave itself to the batteries, inverter and solar panels, all of them will determine how well the appliance runs on your system.