Running Microwave from inverter

[wrwakefield]

Originally Posted by svfinlandia

Bill
Greetings from another Nauticater (NC36).
Just wanted to say that I am surprised that you didn't fry your microwave with a non-sine wave inverter. The spikes from a square wave type inverter are really hard on most electronics, and esp. a microwave.

Al, S/V Finlandia

Hey Al,

Thanks for reaching out. I do enjoy your contributions on the Nauticat forum.

I, too, am surprised the microwave survived the old inverter technology. I knew we would need to replace the inverter [and possibly the microwave] when we bought the boat in May 2014, and finally got around to installing our new inverter in early 2015... [Not that we use the microwave all that much when not on shore or generator power...]

Please touch base if you are ever near our area [SE AK] - we usually have a spare cabin...

Cheers!

Bill

[motion30]

My microwave runs fine on a magnum modified sine wave inverter. It takes a little longer to heat things I'm sure does suck a lot of juice

[mitiempo]

Originally Posted by Frankly

Replacing the Freedom 10 with a Freedom 20 (2000 watt MSW), the inverter shuts down immediately when we start the microwave (go figure).

The inverter is likely shutting down due to low voltage. When you draw 100 to 150 amps from a battery bank the voltage drops considerably if the bank is either older or too small.

[Terra Nova]

Originally Posted by Frankly

...Replacing the Freedom 10 with a Freedom 20 (2000 watt MSW), the inverter shuts down immediately when we start the microwave...

Could it be that you re-used under-size cables?

[mitiempo]

Originally Posted by Terra Nova

Could it be that you re-used under-size cables?

Yes, undersized or too long cables can make the difference as well.

[pitlaw]

MarK
Which model magnum do you have? I have a magnum MS 2000 which is a pure sine wave. I also have the same set up with a 700 watt micro and slightly larger agm house bank. No real problems. The micro needs longer than your typical home micro which is probably more powerful. The noise I have is a typical hum.
Most likly you do not have an inverter issue. Lots of good advice above.

[Salty Mike]

How far from the battery bank is the inverter and what size cables do you have?
In my motor home I mounted it right next to the batts and used cables big as my little finger that was overkill but it gets the job done.

[geoffr]

Here's an odd one which I haven't figured out on our boat.

We have a Xantrex pro 1800W modified Sin inverter. In order for our microwave to work I must turn on a second load (an incandescent bulb) before the microwave will start up correctly - once running it can be turned off! If the bulb is not turned on the microwave runs, but incorrectly (platter turns very slowly and makes an odd noise).

[topmast]

If you look at the modified sine wave on an oscilloscope it looks like a bunch of square waves with the edges rounded a bit. Sort of like ride
ing your motorcycle on rail road ties. Gets you there but vibrates .Lots of digital stuff just smokes.

[misssherry]

Originally Posted by geoffr

Here's an odd one which I haven't figured out on our boat.

We have a Xantrex pro 1800W modified Sin inverter. In order for our microwave to work I must turn on a second load (an incandescent bulb) before the microwave will start up correctly - once running it can be turned off! If the bulb is not turned on the microwave runs, but incorrectly (platter turns very slowly and makes an odd noise).

I had an inverter in an RV that would not start the tv unless a light bulb was turned on to kick the inverter out of standby mode. Seems that your Xantrex is not seeing the microwave as a load.

[smac999]

I have no issues running mircowaves on the 2000w pure sine ones. as above check voltage at inverter. if you have the rc50 screen it should tell you on it.

[StuM]

Originally Posted by smac999

I have no issues running mircowaves on the 2000w pure sine ones. as above check voltage at inverter. if you have the rc50 screen it should tell you on it.

Nor does anyone else.

The problems are with many microwaves and many modified sine wave inverters. And the problem is not the shown AC voltage it is the waveform of the AC and often also the way that waveform varies with differing DC input voltages.

[Wanderlust]

I have a 700W electronic microwave (1150W input), running from a 1500W modified sine wave inverter. The microwave was the smallest and most basic I could find in the store.

It runs OK on the inverter but is noisier than when on mains power. Heating food takes quite a bit longer. I also found that if the house battery bank is down a bit, the microwave will switch itself off (or maybe the inverter resetting itself).

I'm not expecting a long life from this microwave.

[Dockhead]

I think you've gotten your answer already, but I will add one tiny detail --

If your microwave is 900 watts, is that output power or input draw? Those are very different things. 900 watts output is fairly typical of medium sized microwaves, but these will typically need about 1500 watts to run.

So it is possible that you have a power problem as well as wave form problem. Note also that inverters are often rated deceptively. My Victron looks like 3000 watts, but if you read the specs carefully, it's really 3000kVA, or 2500 watts. And that's only at 20 degrees C. At normal operating temperature it's really more like 2000 watts . Now that being said, this inverter does run everything on board without any big problems. I even run a washer/dryer off it while motoring.


It pays to read the specs carefully, before assuming what the practical output is from these units.

And in any case, as others have suggested, it would be a good idea to ditch the modified sine wave and get a true sine wave unit. Many types of equipment will work ok on modified sine wave, but others will not, and the difference in cost is not that great, so why mess with it?