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Topic: Today's Microwave/Inverter Question

Posted By: JoeChiOhki on 12/05/08 04:33pm

Hey Folks, here's my silly question of the day. Microwave, its a 0.7c, 700 watt unit. Is its input wattage 700 watts, or is it higher?

Reason I'm asking is I'm thinking about upgrading to a bigger inverter to run the microwave on periodically when its night. I usually use it to reheat stuff for like 3-4 minutes.

I found a Xantrex Xpower 1000 watt unit for a really good price, but, I need to know if it can handle running my microwave, or if I should go up to the next model up, the 1500.

The microwave is a Emerson MW8871W, standard household type.


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Posted By: ScottG on 12/05/08 04:44pm

That micro uses 700 watts so the 1000 watt inverter should be ok as long as it's not trying to do anything else at the same time. If the 1500 isn't much more, I would go for that just for the added capacity.


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Posted By: JoeChiOhki on 12/05/08 04:46pm

Well, I found the 1000 watt for $50 on clearance, the 1500 is $137. Its a 1000 watt continuous, not surge.


Posted By: Murgatroid on 12/05/08 04:51pm

JoeChiOhki wrote:

Well, I found the 1000 watt for $50 on clearance, the 1500 is $137. Its a 1000 watt continuous, not surge.


Some microwaves have a problem with the cheaper modified sine wave (which is really a modified square wave) type of inverters. It might work. I believe there is also a startup current to contend with, but I think the 1000W inverters have some capacity for that.

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Posted By: Geewizard on 12/05/08 04:55pm

I had about the same size microwave with a 1750W modified sine wave inverter. The problem is the inverter. 99% of microwaves don't like the output waveform of a modified sine wave inverter and tend to only produce about 50% power. That's what I found with mine. I've since installed a pure sine wave inverter and now the microwave can produce a full 1000 watts. There's some references on the web about this issue and a Google will find them. I may have posted some thread on the Forum too, I just don't remember.

Your mileage may vary.


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Posted By: 2oldman on 12/05/08 04:56pm

Good thing you asked..

(as I can see that posted just before me)That inverter is a modified sine wave, which means that your MW isn't going to run very well with it. What usually happens is they run, but only heat at about 50% of normal, so you end up running it twice as long.

3-4 minutes is a pretty good strain on any battery system - even 4-6v golf car batteries. Do you have at least that much?

I would go for the 1500. And judging by the price, those aren't very good quality inverters. Just buying on price is good for your wallet but not so good for what you want to accomplish.


Posted By: JoeChiOhki on 12/05/08 04:57pm

The unit in question was rated as being usable with microwaves, and its made by Xantrex. Normally, its a $129 unit, the company selling it has it marked down for clearance.

http://www.xantrex.com/web/id/23/p/1/pt/29/product.asp

That's the product information on it from the Xantrex company.

EDIT: This is why I posted, I wondered about how well it would work. I have a generator, but I doubt that it would bring too many smiles from folks getting fired up in the evening.

Sadly, I haven't found a Pure Sine wave unit on clearance yet.


Posted By: 2oldman on 12/05/08 04:57pm

Of course it's "usable"..just not very well. We know what we're talking about.

'Marked down for clearance' has nothing to do with what YOU need.


Posted By: JoeChiOhki on 12/05/08 05:04pm

Well, took a quick look at the prices on the Xantrex, Pure Sine 1000 watt units, as well as Samlex 1000 watt.

Looks like I'm gonna have to scrap the Microwave Inverter plan and just run it off the Champion instead, no sense in running the batteries dry if its going to take 6 minutes to do three minutes worth of reheating.

You get much over $200 and it goes right out of my budget range.

Btw, I have 3 deep cycles, two Group 31, and One group 27 for the record.

* This post was edited 12/05/08 05:26pm by JoeChiOhki *


Posted By: travelnutz on 12/05/08 06:47pm

Joe,

We have used a 1000 watt, 1200 watt, inverters in our boats and RV's and the 1500 watt inverter presently in the Lance, along with the 2500 watt that's in the Carrilite 5er and all have run the RV's microwave and it never took double the time to cook the same things as we do when on shorepower. Our 1000 watt and 1300 watt microwaves in our home sure do cook faster but it's due to higher wattage. Our 750 watt Vector Inverter wouldn't operate the previous camper's 700 watt microwave but it would run the 800 watt coffeemaker with the same brewing minutes as shore power. It had made many pots of coffee and I still have the inverter as it's used in our Vee nosed enclosed trailer.

Id sure go for the 1500 watt as it can be used for an 1100 watt toaster, 950 watt coffee maker and other things also. We use a 1350 watt toaster oven in the Lance as our toaster on the 1500 watt inverter as it has so many other uses than just toasting bread.


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Posted By: Matthew_B on 12/05/08 06:50pm

The 700W rating is the output. Look at it as one case of actually rating the microwave at what the customer wants: how much power it actually puts into the food.

So first you have to add in the losses in the magnetron and power supply. But that's not all. Magnatrons are unstable when feed from a fixed voltage. So the transformer based microwaves limit the current to the magnatron though a whole bunch of series inductance in the design. This means that there is a phase shift and the power factor is bad. There are amps flowing that don't deliver power. Still not done..... The current draw is also very non-sinusoidal. Even more of a power factor hit.

You'll find that the 700W microwave needs at least a 1500W inverter.

A cheaper alternative is to pick a microwave that's an "inverter" model. By "inverter", they mean that there is a switching power supply to convert 120V to the 2.5kV the magnatron needs. "Inverter" has nothing to do with feeding it 12V. This is good for two reasons. #1, they are much nicer to cook with. Instead of the scorch - pause - scorch that transformer microwaves have when set to low power, you get 10 real power levels. They are much, much nicer to cook with! #2 - They will run on a MSW inverter only a little bigger than the microwave rating.

The added price for a inverter microwave will save the difference in price between a true sine wave and MSW inverter.






Posted By: Geewizard on 12/05/08 07:13pm

Matthew_B wrote:

The 700W rating is the output. Look at it as one case of actually rating the microwave at what the customer wants: how much power it actually puts into the food.

So first you have to add in the losses in the magnetron and power supply. But that's not all. Magnatrons are unstable when feed from a fixed voltage. So the transformer based microwaves limit the current to the magnatron though a whole bunch of series inductance in the design. This means that there is a phase shift and the power factor is bad. There are amps flowing that don't deliver power. Still not done..... The current draw is also very non-sinusoidal. Even more of a power factor hit.

You'll find that the 700W microwave needs at least a 1500W inverter.

A cheaper alternative is to pick a microwave that's an "inverter" model. By "inverter", they mean that there is a switching power supply to convert 120V to the 2.5kV the magnatron needs. "Inverter" has nothing to do with feeding it 12V. This is good for two reasons. #1, they are much nicer to cook with. Instead of the scorch - pause - scorch that transformer microwaves have when set to low power, you get 10 real power levels. They are much, much nicer to cook with! #2 - They will run on a MSW inverter only a little bigger than the microwave rating.

The added price for a inverter microwave will save the difference in price between a true sine wave and MSW inverter.


Matthew, do you have a source for switching PS microwaves? I tried to find one to no avail when I was searching for alternatives to a pure sine wave inverter. Of course, this is Alaska and I looked in 2004. Probably a lot out there now.

(edited) FYI: I did a web search for inverter microwaves and it seems Panasonic is the most well known brand. However, the consumer reviews rate it very poorly because they break down so often and sometimes last only 3 months. Any others out there known to be more long-lived?

* This post was edited 12/06/08 01:50pm by Geewizard *


Posted By: travelnutz on 12/05/08 07:24pm

Matthew,

I don't know if i'd agree that it takes a 1500 watt inverter to run a 700 watt output microwave but it sure would be the wise choice to have. Our 1000 watt inverter would run the microwave but the light bars indicator would all be bright meaning it was maxed out. The 1200 watt inverter had a needle indicator and it wouldn't be pinned but not far from it. Neither are very scientific measurements but are a reasonable indicator of power use.

I sure do agree that the 1500 watt inverter is the way to go so it's not stressed to the max as we don't know the actual watts draw his microwave will have.


Posted By: JoeChiOhki on 12/08/08 09:28am

Matthew_B wrote:

The 700W rating is the output. Look at it as one case of actually rating the microwave at what the customer wants: how much power it actually puts into the food.

So first you have to add in the losses in the magnetron and power supply. But that's not all. Magnatrons are unstable when feed from a fixed voltage. So the transformer based microwaves limit the current to the magnatron though a whole bunch of series inductance in the design. This means that there is a phase shift and the power factor is bad. There are amps flowing that don't deliver power. Still not done..... The current draw is also very non-sinusoidal. Even more of a power factor hit.

You'll find that the 700W microwave needs at least a 1500W inverter.

A cheaper alternative is to pick a microwave that's an "inverter" model. By "inverter", they mean that there is a switching power supply to convert 120V to the 2.5kV the magnatron needs. "Inverter" has nothing to do with feeding it 12V. This is good for two reasons. #1, they are much nicer to cook with. Instead of the scorch - pause - scorch that transformer microwaves have when set to low power, you get 10 real power levels. They are much, much nicer to cook with! #2 - They will run on a MSW inverter only a little bigger than the microwave rating.

The added price for a inverter microwave will save the difference in price between a true sine wave and MSW inverter.


At 700 watts of output Matt, I've yet to have a moment where I actually needed to turn down the power , usually I have to add on a minute or two to the cook time. Not certain if that's entirely the microwave, or the fact that the camper's on 75' of 12 gauge extension cord.... (I'm setup for 20amp hookups, vs 30).


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