Question about Panasonic "inverter" microwaves

[Cybrvanr]

Panasonic claims that it actually reduces the amount of power delivered to the magnetron on their inverter microwaves, instead of just cycling it on and off like other makes do.

Now, here's the dilemma I am up against. I have a 1000 watt power converter in my camper that converts 12 volt power (from 2 golf car batteries) to 120 volts power. A long time ago, finding microwave ovens that consumed less than 1000 watts was easy to find. The problem is now, pretty much all microwaves produce enough radiation to wipe out a small Japanese city. My idea is to install an inverter microwave in the camper, and then just run it at half power or less, thus keeping me within the 1KW maximum limit.

 

[sudsmaster]

Interesting question.

I'd have to hook a watt meter up to my Inverter. Maybe in a few days, unless someone else beats me to it.

 

[ttuee2006]

Microwave Wattage

Let's be reasonable here folks. Read the wattage information on the nameplate of the microwave itself. Doesn't list it? Multiply the amperage rating by 125V and you'll get your wattage. As a rule, if the microwave is a "1000 Watt" unit, it CANNOT pull less than 1000 watts regardless of what technology is uses. You can't get something for nothing. If you've got a 1000w capacity, you're looking to get a 750W or smaller microwave. Plain and simple. It doesn't matter what kind of microwave it is.

 

[sudsmaster]

Eric,

Actually, it may matter with the Panasonic inverter. Since it doesn't reduce power by cycling on and off, but rather by reducing the wattage of the magnetron, the overall current draw may well be lower at 50% power than at 100% power. Probably not 50% lower, but that will require some testing.

It's like a dimmable light bulb. It draws less wattage at a lower light setting.

 

[sudsmaster]

OK, I did some tests.

Panasonic Inverter Genius 1.6 cu ft 1300 watt

Measurements with "Watts Up?":

Full power: 1.9 kW
70% power: 1.4 kW
50% power: 1.1 kW
30% power: 0.7 kW

At power levels in between these, the power cycles lower than the level but never completely off.

The readings are probably approximate since the Watt's Up? says it's only good to 1250 Watts. (1.25 kW). But I think it's close enough to demonstrate lower power draw at lower power settings.

1.9 kW would be about 15 amps at 120 volts.

 

[panthera]

That is an efficiency

which is out of this world - you get back 2/3 for every 1 watt you put in.

Outstanding!

 

[ttuee2006]

Now here's the kicker...

Did the Watts Up! device measure pure watts or did it measure the VA draw? Yes, it does matter. The inductive components of the microwave (magnetron, fan, blower, etc) all add a reactive component to the current draw. The VA draw will always be higher than the normal "wattage" draw and can easily exceed the limits you have on the inverter. If the person with the Panasonic Inverter mwave can redo the test measuring their voltage and current draws at these levels it'll be a much more meaningful result than pure watts.

For what it's worth.......yes it DOES matter.

I still think for your application, you're better off getting a microwave that's smaller than your inverter capacity. All it's going to take is someone to forget to set it at half power and poof.....no more inverter!

Also worth considering is how "clean" is the sine wave coming out of that inverter? Usually they're pretty trashy and meant for running power tools and such. If it's a "noisy" sine wave, you can easily toast the circuitry in that microwave, especially if that inverter in the microwave interferes with the circuitry in the inverter itself! (I work at a company that makes voltage regulators....believe me.....I know my shit about this subject! I deal with it every single day explaining the same things day in, day out.)

 

[Cybrvanr]

WATTS UP meters I think will measure both VA and true wattage. I know they have a power factor, and they have correction built in for it's measurements. They will also measure pure amperage too...they are pretty fun little gadgets!

This is perfect information though. The Panasonic Inverter microwaves DO run less juice in when scaled back The power converter in my camper is measured in true watts, and it looks like that I won't be able to get the power down low enough in the microwave to be within the usable window of the converter, and still have the microwave be useable. 30% power will be simply too little power I think. Maybe if I upgrade the converter to a 1500 watt model, it might work better. That would get me into the 70% range, where the microwave would be very useful.

Still, I'm surprised that microwave ovens are as inefficient as they are. Yes, 2/3 of the input energy is going to radiation energy, but that's pretty bad when you consider a conventional oven is near 100 percent efficiency (power that goes in gets converted to heat energy) Most elecric motors are in the 85-90 percent range for efficiency.

 

[sudsmaster]

My Watts UP? meter measures just watts. I till convert them to pennies if you input a cost per kWH.

It does not measure amps directly. You can compute the amps by dividing the watts by the volts, more or less.

It does not measure volt-amps either. Just the watts, just like the meter outside your house.

 

[panthera]

Steven,

Efficiency is not the be all and end all of cooking - at least, that was Amana's defense way back when. I agree, when you consider that the power conversion of resistance elements is 100%, this seems lousy.

That said, what counts is how much of the energy consumed is converted into cooked food. There, microwaves are better at many things than other cooking methods.

May I make a suggestion? If the microwave isn't going to do it, why not try using a pressure cooker? They are often faster than a microwave and need very little heat to reach operating temperature.

 

[toggleswitch2]

WAIT! STOP THE PRESSES.

I need a 'slapantion of the difference between watts, VA and power factor. SPEAK SLOWLY! LOL

Would you just look at those prices! I did a search for 12v appliances.

http://www.autotrucktoys.com/semi-truck-accessories/RoadPro-Semi-Truck-550-Watt-Microwave-and-800-Watt-Power-Inverter-Package-PRD13575.aspx

 

[toggleswitch2]

LOL

65a @ 12v

OutdoorGB - the Outdoor Equipment Specialists

To do description base controler - take code from Head

www.outdoorgb.com

 

[toggleswitch2]

uhm... can't inverters handle a 3 to 4 minute overload? (i.e. enough time to zap a plate of food in a lower powered m-waver).

Only 90 pounds sterling!

12V In-Car Microwave Oven - fast food for trendy travellers - The Red Ferret Journal

This 12V In-Car Microwave Oven proves that you can never make ‘em too small, or too black for those travellin’ treats. Plug it into your cigarette lighter socket and roast that hog on the hoof. £89.98. Meals on the move! · Compact and portable · Fast cooking speeds · Powered via 12V cigarette...

www.redferret.net

 

[panthera]

Steve,

I will try. Let's hope this goes better than the split-phase question.

OK. If you are talking about direct current, then VA=W...volts * amps = watts. Watts mean work. As in sweaty horses, perspiring men and glowing ladies type work.

There is no power factor correction in that simple formula.

When you go to alternating current, things can get interesting.

As long as the load is purely resistive, you are safe assuming a power factor of 1 (power factor is expressed as a percentage). As soon as a load is reactive, the ability of the circuit to do work and the actual load on the circuit are going to be out of sync. The power factor will be less than 1, tho' greater than 0.

The power factor reflects this difference between apparent power (volts * amps) and real power, the actual work done.

Since microwave ovens are very reactive loads, you need to know the VA and the power factor to determine the real life work the inverter needs to do.

Interestingly, it is relative easy to bring things back into sync, either passively (if the load is inductive, put in a capacitor and vice-versa)or actively, which can bring you back to a situation where current and voltage are not out-of-sync.

Does that help? Wikipedia has a decent article on the subject...

(And, yes, I could see this thread getting very slutty very fast between us.)

 

[ttuee2006]

Ok.......I'm done!

Education aside, it's apparent that the "smart people" on this forum simply "know much more" than I do about my everyday profession!

Enjoy the sweet burnt smell of your inverters people!

By the way, if the original poster would like a LOGICAL, and CORRECT explanation of why I say what I do and the logic, math, and physics behind it in an UNDERSTANDABLE way, by all means.....email me!

 

[panthera]

Eric,

what bug crawled up your ass? Nobody is attacking you here and I have read no disagreement - in fact, I voiced the same view, if somewhat more reservedly, as did you: It is not a good idea because the sine wave the microwave needs is not going to be the dirty, unstable saw-toothed jiggery-pokery it will probably get?

By the by, several folks here are either electricians, electrical engineers or (my case) work in the natural sciences.

 

[ttuee2006]

No Bug Here...

No bug here, just the responses of some of the "experts" above.

I'm more or less a combination of all of the above in your last post. I work in the engineering/problem solving department of a generator voltage regulator manufacturing company. I literally deal with problems similar to the above every single day, just in a much larger scale.

I ask for information, I get ridiculous posts from "know-it-alls" discussing the merits of a plug-and-play device of which they don't even understand!

There is SO much more going on behind the scenes in this particular scenario than just watts or amps. So much more...

Long story very, very short: A traditional microwave less than 1KW total load will work for your application. The inverter microwave most likely will not. If it does work (which is quite possible) the microwave or the inverter will not last long. We're talking seconds to minutes of life expectancy here. Even a high-quality oversized inverter will have difficulty with the inherently choppy/spike-riddled waveform that the inverter microwave will produce.

I should really check my files and see if I have any O-Scope files that show the types of sine-wave destruction that happens from inverter-on-inverter situations.....it is NOT pretty and usually results in explosions or short-circuits.

 

[sudsmaster]

Eric,

Well, sorry if my answer to your "question" was so annoying to you.

You asked if the Watts Up? devices measures volt amps. I replied that it does not, it measures watts. I can't find the owner's manual the moment (it's around here somewhere), but I did find the original box. On the back it says:

"State of the art digital microprocessor design utilized high-frequency sampling of both voltage and current measurements for true power. Power factor is captured so even phase-shifted loads such as motors are accurately measured."

Remember, the Watts Up? is designed to measure how much an electrical device will COST to run. In virtually all residential consumer applications, the cost of electrical power is per WATT, not per VOLT-AMP.

Frankly I don't know you or what your qualifications are, but in general I tend not to trust someone when they get defensive about what they say they know. I've avoided telling CBVanr that his inverter will work with a panasonic microwave, I just told him the results of my tests. Sorry if that runs contrary to some dogma. Personally I'd go looking for a bigger power inverter and a small, cheap low power mwave to run off it. Walmart should have something along those lines, I would think.

PS-I also have formal education in electronics and a fairly substantial scientific background. But no, I don't make transformers for a living.

 

[toggleswitch2]

Sorry If I have been an @$$.

Simply looked at what is available in 12v, and I asked if inverters can withstand a temporary overload, as generators say they can.

Will re-read this thread to be sure I have caught the technical subtleties.

Thank you for your patience!