Modified or pure sine wave inverter for microwave?

[WalkaboutHubby]

Hello all,
I'm just starting (so far just in my head) my build.  I've decided that I must have a microwave for short bursts for several purposes.  I know that in a perfect world that a pure sine wave inverter is best, but the cost for one that will run a microwave is very high.  So here is my info and then questions.

I will have 540 watts solar, and a 100 watt portable if I need it..  I will have 400-440ah of golf cart batteries.  The microwave is 700 watts. That will be my highest use electrical appliance.

How many watts, steady and peak should my inverter be?

Can I get away with using a modified sine wave inverter?

 

[Putts]

Microwave ovens come in various sizes with substantially different current draw. Can you find the current draw required for your nuker?

 

[ZoNiE]

Regardless of Amp Draw, use a Pure. A Modified can fry the microwave and/or it may not even run at all.

 

[Hermes1]

Microwaves are one of the appliances where a pure sine wave inverter is needed. Since you mention a microwave is important for you, invest in a pure sine wave to properly operate it and you the upside is you won't have to worry about any other electrical items you may use.

 

[WalkaboutHubby]

The microwave is one of the old fashioned, simple, non digital dial ones. I was wrong, it is 600 watts, drawing 850 watts. It was about $50, if I recall.

 

[WalkaboutHubby]

My wife had a brilliant idea of making popcorn with the microwave on the house alternating current. Then when it cools off this evening, we'll bring the microwave out to her van (300ah battery with 2 gauge cables to an 1100w/2200w peak Krieger inverter.

She's the rocket scientist in this home. I'll post the results.

 

[tx2sturgis]

Huh. :huh:


I've been running small microwave ovens on cheap modified sine wave inverters for at least 10 years...yep...they buzz and get a little bit hotter.

So what?... its a $50 microwave and a $100 inverter.

When you fire up the microwave and inverter, it will make a lot of noise on nearby radio receivers and maybe even wipe out the XM radio and the TV....but its only for a few minutes...then life gets back to normal.

 

[Optimistic Paranoid]

The simple truth is that it's impossible to predict whether a modified sine wave inverter will work or not.

Take cordless power tools. Porter-Cable, Dewalt, Ryobi, Craftsman, etc.  Some people here have reported that they can recharge their batteries with a msw inverter.  Others have reported that their batteries won't charge on one.  Depends on how the engineers designed and built the charger.

I suspect the same is true of the inverters themselves.  Different brands designed and built differently.

The same is probably true of microwaves.  Some will work, some won't.  No real way to tell without trying it.

Buy an mss inverter from someone who will take it back and exchange it for a psw inverter if necessary.

And don't be completely surprised if the msw causes the magic smoke to leak out of the microwave.

 

[tx2sturgis]

BTW when I said 'cheap' I mean that as 'inexpensive'...not junky....

Inexpensive compared to pure sine.

There are literally millions of modified sinewave inverters powering the microwave ovens in the sleeper compartment of OTR tractors running all over this country.

It can be done and IS done all the time. I did it for at least 10 years, probably more like 15, over the course of 3 or 4 tractors, more than a million miles, and thousands of quicky meals. It worked on 3 different ovens and 3 different modified inverters.

Our ENTIRE fleet of over 8000 tractors run almost exclusively modified sine wave inverters for the microwave. A few drivers with sleep apnea will run the CPAP on a 300watt pure sine inverter, that's the only way they can stay in compliance. But it is separate from the generic 1500 or 1800 watt modified sine inverter.

Over the road tractors normally do not have solar, but they do usually have 4 large truck batteries and sometimes an APU (auxiliary power unit). We always have plenty of current available. That's the secret. You wont have good luck with one battery because the inverter will sound the alarm that the input voltage is low and your inverter will probably shut down.

If you are buying a $900 microwave then by all means power that thing with good clean expensive pure sine waves.

But for the rest of us mortals, you can get by with much less.

 

[Weight]

Pure sine wave inverters are getting lower in cost.

 

[tx2sturgis]

Pure sine wave inverters are getting lower in cost.

True that. They are becoming a consumer commodity.

I own a couple of them and they are much better for running sensitive electronics, and of course, medical, audio, and video equipment.

But if you are willing to tolerate a little bit of buzzing, a less expensive msw inverter will run a normal, low end, lower power microwave just fine. They do tend to cook just a little bit slower, but whats 5 minutes vs 4 minutes for a bowl of soup?

Now if you were trying to roast a 10 pound turkey in a high power and expensive convection microwave like you see in modern motorhomes and nicer RVs, then yep...you should use a nice, high quality pure sine inverter.

 

[akrvbob]

I'm going to say I only recommend Pure Sine Wave. I have run a micro off a modified, and I know others have as well.

I don't reommend it, spend the money and get a Pure SW

I've used this $415 2000 watt PSW with my microwave for many years and it performs perfectly! Find it here:

http://amzn.to/2vNsNji

Hopefully Jim in Denver will join in, his inverter is cheaper and also works perfectly but I don't remember which one it is.

 

[tx2sturgis]

I wonder if anyone has tried one of these 12v microwaves?

I have not...but it seems like a good idea.

Years ago, RoadPro had one at they sold at the truck stops but I didnt need one at the time, and they seem to have disappeared.

The website here shows out of stock, but worth a look anyway:

http://www.roadtrucker.com/12-volt-microwave-wavebox/12-volt-dc-microwave.htm

 

[WalkaboutHubby]

The not-so-scientific results are in. I used my wife's van (so you don't have to look back, 300ah batteries connected with 2ga cables to a Krieger 1100w modified sine wave inverter). There are many variables. Since we're past sunset, there was no power coming in from the solar panels. The starting system voltage was 12.6v. It was well over 100F all day (for most of the last 2 months, up to 110F), so the batteries are pretty warm. At the inverter, while cooking, the voltage registered at 11.6v, simultaneously, the the voltage on the battery panel read 12.1v. In the middle of popping the popcorn, with suggestion from wife, I turned on the engine, which brought the voltage up. The microwave noise level was about the same on inverter current vs the house alternating current.

Between the increased time and the decreased popped corn yield, using the MSW inverter and batteries took 44% more energy. And the vehicle popcorn looked "soggy".

I'm not planning on making popcorn on my travels, just using the microwave to heat things up. But, since I haven't yet purchased an inverter, I guess I will pay the premium for a pure sine wave.

Now, to pick one out should be interesting. Any recommendations for a 1000w PSW inverter? Thank you,
Steve

 

[Cammalu]

Now, to pick one out should be interesting. Any recommendations for a 1000w PSW inverter? Thank you,
Steve

Nature Power 1000 watt inverter from Camping World is working fine in my RV. I can't recall exactly what was spent but it was under $300.

I had originally ordered from renogy but they sent me the wrong one and I didn't want to wait forever for a new one. Gotsmart installed my system and was real pleased with everything.

As I've only had this about a month I can't speak for long term use.

 

[Optimistic Paranoid]

Now, to pick one out should be interesting.  Any recommendations for a 1000w PSW inverter? Thank you,

Do you have, or do you plan to get, solar panels?

In addition to having low voltage cut-off, inverters also cut off if the voltage is too high.  Most inverters have a cut-off value of 15 something volts, which works fine on just batteries or on batteries plus alternator.

However, solar panels, on a bright, clear, cool morning, can exceed that, and you will find your inverter won't run because the solar panel voltage is too high.  A few inverters have a high voltage cut-off value of 16.5 volts, and those are the ones you want if you've gone solar.

For example, Samlex is a good company.  Their PST series of inverters has a high cut-off of 16.5 volts.  Their SSW series has a cut-off of 15.3 volts.

BTW, it was Handy Bob who first turned me on to this fact:

https://handybobsolar.wordpress.com/inverter-issues-spring-2013/

 

[blars]

Panasonic "inverter" microwaves reportedly work fine off MSW, every other model and brand does not.

When my 2000W MSW inverter died, I bought a 2000W PSW from aliexpress direct from china for less than $200. Microwave much happier.

 

[jimindenver]

The Pure in pure sign wave is a buzz word. It is intended to mean cleaner and one company uses the term TRUE instead of pure. Then again on the opposite end of things, some MSW inverters are clean enough for anything, others are just miss labeled Square sign wave junk. Without a scope you will never know.

I use a Trip-lite PV1250fc MSW industrial inverter. It runs the microwave just fine as well as my A/C, chargers, TV, Satellite receiver. It does create a slight buzz in the Little A/C's fan but otherwise has run it fine for years. You can get it for $288 shipped with a extended warranty.

There are other higher end MSW inverters, they are usually more expensive than the junk.

My last MSW inverter was of the type to really be square wave. It did cause my chargers to get hot, my satellite receiver to get really hot and my TV had lines in the image.

 

[Optimistic Paranoid]

Here's an interesting blog post on msw vs psw.  I was particularly interested in the oscilloscope pictures of the difference.

https://www.altestore.com/blog/2015/10/pure-sine-wave-vs-modified-sine-wave-whats-the-difference/

 

[tx2sturgis]

The Pure in pure sign wave is a buzz word. It is intended to mean cleaner and one company uses the term TRUE instead of pure. Then again on the opposite end of things, some MSW inverters are clean enough for anything, others are just miss labeled Square sign wave junk. Without a scope you will never know.

I use a Trip-lite PV1250fc MSW industrial inverter. It runs the microwave just fine as well as my A/C, chargers, TV, Satellite receiver. It does create a slight buzz in the Little A/C's fan but otherwise has run it fine for years. You can get it for $288 shipped with a extended warranty.

Here is another good point.

A cheap 'pure sine wave' inverter can get pretty crummy sinusoidals during a heavy load...where a GOOD quality 'modified sine wave' inverter is hardly phased, and if it is, the wave forms can actually 'soften up' and become a bit more 'rounded'  under a heavy load.

I have been perfectly happy running an inexpensive microwave on a good quality MSW inverter for years. It can be done.

If the cost difference is spent on batteries and cabling, its a viable solution. IF money is no object, then of course, buy a GOOD quality pure sine inverter, and not the cheapest pure sine inverter you can find. Stick with the known brands.

Or so it seems to me.