How big of an inverter for microwave?

[Bad Obsession]

If I was going to put an inverter in my boat to run my microwave occasionally while at anchor what size inverter should I get? What would be the most economical solution?

I am thinking that this would be done once in a while if not rarely. I usually don't even think of using the microwave but the thought has just crossed my mind. The other thing is that I have a small microwave on my boat.

My house power bank is descent and it is monitored by a Link 10.

 

[Chuckbear]

We run our microwave quite often on the inverter. Our former boat had an 1800 watt and I have just installed a 2000 watt on the new boat. Although I believe it would run on a smaller one I don't think it would be very efficient. It did struggle a bit on the small inverter, and no neither of these were pure sine wave and the microwave lasted for years, actually is still working for the new owner. Chuck

 

[seadaddler]

More Info

Need more info on how much the microwave draws but even more in important is the size of the battery house bank.
You need to do the math how much the microwave will draw and how much your house bank will be used.
I have a 2000 watt inverta hooked up to 2-4D's at I think and when using the microwave the house bank does not go below 50% but does use a lot of battery power.
Nick

 

[Paul F]

Have a small 700 watt inverter from Harbor Fright peaks to 1800 watts. It runs the small microwave just fine. But as others have said expect a large battery draw. I normally run the engine/alternator while running the microwave to offset the battery draw down. Have however run the micowave for more than 10 minutes off the house batteries without a problem.

 

[Stu Jackson]

"Expecting a large battery drain" is like wishing for the tooth fairy!

It's also misguided advice.

It's really simple math, folks, not something unusual. West Marine has a good description in their Advisors: http://www.westmarine.com/webapp/wcs/stores/servlet/westadvisor/10001/-1/10001/Inverters.htm

It's something not really hard to do, like converting watts to amps, figuring how much time your microwave is going to run, converting the AC to DC by using a factor of 10 or 12 to include the inefficiencies in conversion, and it's simple.

If you have a 200 ah house bank, and you haven't run your lights all night long, and you haven't watched a 120V TV from night time to dawn, running a microwave on an inverter will not kill your house bank.

Fact is, if you've been using your boat for a few years, you should already know what's up with the electrical system. Having the Link 10 is a very wise move.

We have a small (physical) microwave and it works just fine on our Freedom 15 1500 watt modified sine wave inverter. I say physical size for the microwave since it was there when we bought the boat and I never have removed it to check the nameplate. I figured since it was a small microwave it would have a small electrical load. Our small microwave takes 82 to 86 amps when it is running for short periods of time, based on our Link 2000 readings. So less than five minutes for a bag of popcorn uses up around 8 amp hours (5 mins./60 mins per hour) X (90 amps). If you can't handle THAT load, you have bigger electrical problems than an inverter and microwave!

Just do the math for selecting your inverter. In fact, since they come in only a few varieties of sizes, what you need to do is the math to figure out how to avoid buying one that's too small.

You'll also need to decide if you want to wire it into the boat's AC electrical system, in which case you'll need either an inverter with an internal transfer switch or a separate switch like this: http://c34.org/bbs/index.php/topic,833.0.html. I find that spending all sorts of $$ for an inverter and then needing to have extension cords run around inside the boat to use it makes little sense to me.

 

[Ron20324]

You can find microwaves at around 800 to 850 watts. I found a nice little one like maybe on the coffee counter at work at a goodwill store.

 

[r.w.landau]

Make sure the wiring to the inverter will handle it. 2000 watts at 12 volts is 166 amps. That can make wires really hot really quick. 12 gage wire is designed to handle a 20 amp load. #4 will handle 100amps provided the length of run is 10' or less.
That is alot to draw out of a battery at one time.
r.w.landau

 

[txtowman]

generally you can take the rated watts multiply by 1.25 this will give a close estimation of required input. for example my 1100 watt requires 1500 watts to run efficiently but will struggle on a thousand watts. make sure the inverter is rated for "continous" output
some say 1000 on the box but that is the surge watts.

 

[Bill Roosa]

Watts is watts

An 800 watt (120 volt) MW will still draw 800 watts at 12 volts. At 120 volts it draws (P=V*A) 800/120=6.67 amps, at 12 volts it draws 800/12=66.7 amps!!

You might notice though that batteries are not rated in watts. To get to Ah you need to know the time the MW runns. For 10 munutes (10/60 hours) at 66.7 amps it would draw (10/60)*66.7=11.1 Ah. For a 100 Ah battery bank that is about 10% total capacity or 20% working capacity!!!!!!!! For a 400 Ah bank it would be 2.8% total or 5.6% working capacity.

Size does matter.

 

[Don12364]

Just read the wattage off the label on the back of your microwave and this is the power of inverter you will need. It is unlikely that you will find an inverter of exactly the power of the microwave so just go to the next size up. I would caution against going too high in power as static inverters are incredibly power hungry.
I have an 850 watt microwave which runs perfectly well from a Freedom 1000 watt static inverter. It draws 74 amps!
You will need either a 'modified sine wave' type or a pure sine wave one.

Tips:-
If cooking for more than a few minutes then run the engine to have the alternator put some power back as the inverter draws it out. This way you do not deplete the house bank too much. My microwave draws 74 amps but this reduces to 35 amps with the engine on at fast idle.
Also switch off the inverter when cooking is done because microwave cookers keep their magnetron heater powered up all the time, even when they are 'off', and this takes quite a bit of power over time.

 

[wufibugs]

The least power hungry microwaves are now 700 watts. Got one on black friday for $24. Course lower power means longer cooking times, so for a boat, there may be little difference ultimately if you have the extra inverter power. Don's point about "standby" mode causing a constant battery drain applies to several appliances including most TVs and radios. I suppose I should install a power shut off switch to the outlet for the micro to account for that.

 

[Jim2798]

Don't overthink it...

Simply unplug the little devil!

 

[zeehag]

mine took a suicidal swim LOL...i use nothing that sukks electricity on my boat as i know the difficulty in making the banks return to good after the one cup of coffee is made LOL..why not just use the stove and then have a warm cabin also???? uses far less juice, then there is some left for bilge pumps LOL.....i used my liveaboard experience for getting into the cruising mode--i use nothing i would not use while underway and keep nothing on board i will not ever use .....

 

[Ken Honeycutt]

On my old Hunter I installed a Chinese 2000 watt inverter off ebay (not marine rated) for a lot less than the marine type. Worked fine for the 2 years I owned the boat running the microwave, vac cleaner and other assorted tools. There probably is some reason why you shouldn't install one of these but I never had a problem.

 

[wufibugs]

Jim, I'm not a big fan of turning devices on and off by plugging and unplugging them because I think the plug ultimately get lose. Also, the plug is in the cabin ceiling and I don't like having wiring hanging all over. While I am rewiring, I will just create a dedicated outlet/switch combo for the microwave. Is the draw just the ubiquitous clock, or is there some other part of the oven that is in standby mode?

 

[Stu Jackson]

If you have a Link 1000 or 2000 you can use it to turn the inverter off.

If you don't have a Link, then you can use the switch on the unit (at least my 1998 Freedom 15 has a switch on the unit for the inverter - if you don't have a Link X000, then the charger goes on whenever you plug in).

And turning off the AC breaker is also a plan.

This is not an issue.

 

[Migrant III]

use of inverter generator

There are several 2000 and 3000watt inverter generators on the market. Would it not be simpler to use one instead of getting into the expense and storage, and strapping them down well, of clunky batteries? Marinas as getting so expensive, ($60 a night at Port Dover, Ontario, if I remember correctly from last summer). I am planning to use the Honda 3000 and use it to power my inboard electric motor which only cost $3000 US and all onboard power including an 1100 watt GE microwave. The gas saved (instead of the Evinrude 9.9) will be half.
Anyone care to comment, advise?.

 

[Benny]

An inverter is most efficient when its size is matched to the load. I would provide a 20% cushion to allow for variations. So to drive a small 800 watt microwave I would use a 1000 watt inverter. I would not size an inverter for a boat just based on the microwave oven. I would look towards the maximum requirements like flourecent lights, refrigeration and TV/DVD units. I run a 1500 watt inverter and can accomodate all my needs.

 

[Ross]

I sometimes wonder how I have lived for 70 years without a microwave cooker. My grand daughter was speechless when she learned that we don't have a microwave in our house. I told her that I do have a computer and a cellphone and she said doesn't everyone?

 

[Benny]

Ross, there is not much to wonder. I do not refer to a microwave oven as a cooker as it does not do a good job at that. It is a great tool for heating and its value aboard a boat is the convenience it brings. We have learned through the years that it is much easier to cook at home than in the boat. So we cook at home and reheat food in the microwave oven. There is no nostalgia in not having to wash pots and pans. Meats are done on the grill, breads in the propane oven and eggs are fried on a skillet but everything else pretty much goes on microwave.