Slow microwave ovens

Shouldn't we have faster microwaves by now giving out a few kW? They were invented decades ago.
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On 12/29/2018 7:43 AM, William Gothberg wrote:

Higher powered microwaves would require higher powered electric outlets, probably 220VAC (in the USA).
Also it is questionable whether higher powered ovens would be practical for use. Getting warming times down to a couple of seconds might not be a good idea. More speed is not always better.
Bill
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On Saturday, December 29, 2018 at 9:23:42 AM UTC-5, Bill Gill wrote:

hey

+1
That about covers it. Not sure how useful more power would be. For exampl e, last night I was thawing out a tomato sauce in a quart plastic container. The Panasonic has a defrost mode that uses about 30% power and cycles that. Even so, after a couple mins you have to check, because the bottom gets hotter and the plastic can soften or melt. Other things tend to heat uneve nly as well, eg you can have one area starting to spatter, while the other is lower temp. If you had more power, those issues just become worse. And for sure the fact that receptacles are 15 or 20 amps limits the practical upside as well. If people had a MW and it trips the breaker when they use another small appliance, they wouldn't be very happy.
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That's not really true anymore. The newer "inverter" style microwaves actually reduce the power level.
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That was true of the first generation of Microwaves, but the current "inverter" driver units actually CAN throttle the power. Inverter microwaves are much better for defrosting AND cooking.
We've had ours for about 2 years now - replacing our original that we bought in about 1985.
BIG difference (but the old one would likely still be working by the time this one dies)
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Why is it called an invertor? I thought an invertor was a device to increase the voltage - like running 240V devices off a 12V car battery.
And why on earth would you not want to cook on full power? I've never had a reason to lower the power from the maximum of 800W. I want the meal as soon as possible!
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Typical microwaves use fixed AC power to drive the magnetron. Inverter driven magnetrons use DC power, which can be variable.
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So they rectify the AC, then boost the DC voltage as required by the user setting?
But even without an invertor, surely you could have a few tappings on a transformer to change the AC voltage to the magnetron? It's not like you need infinite control, just 3 or 4 would do.
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On Sat, 29 Dec 2018 12:27:21 -0600, Arthur Conan Doyle

No, the inverter still produces AC - but the AC is variable. The AC in both systems is rectified to DC for the magnetron.
The inverter produces a lot higher frequency AC than line frequency. High frequency produces a much easier to filter DC .
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wrote:

Wrong.
Both styles actually take AC incoming mains, raise it to 5k or so, and convert it with a single diode mind you, to DC to feed the magnetron. The filament is fed by low voltage AC. Neither of them can or do vary the voltage going to the magnetron. That's just not how it works. You can't lower the voltage to reduce microwave energy. And you can't raise it to get more microwave energy, either. The magnetron requires voltage within a certain range to function. More than that will burn the magnetron up. Less will prevent it from making viable microwaves.
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On 31/12/2018 07:18, Diesel wrote:

So what is the difference between inverter and non inverter types? Is 'inverter' an appropriate term? How do either control the power?
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Max Demian

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On Monday, December 31, 2018 at 9:43:22 AM UTC-5, Max Demian wrote:

He abundantly and mostly correctly explained that in his previous post, including the one you copied. The inverter type still pulse the magnetron, just at a very fast rate, so that for all practical purposes, it's like being continuous. It's like dimming a 100W bulb. If you turn it on and off half the time in 1 second cycle times, you will see it blinking. If you do that with a very fast cycle time you will see a dimmed but continuous light. That's how bulb dimmers work too.
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On 12/31/18 9:12 AM, trader_4 wrote:
[snip]

I built a PWM dimmer as a project I did in college. The improved efficiency was obvious if you felt the heat in the power transistor. Too low a switching frequency would show the light on for part of the time.
Also, with AC, a diode in series reduces the brightness (approx. 49% duty cycle). This works on some LED lights as well. I have them on some Christmas lights that are normally too bright (green tape lights around tree and light pole in picture below).
http://notstupid.us/include/picviewer.php/graphics/xmas2018?seqno=5&desc=XMAS2018&back=/winter.php&backname=winter+holiday+2018
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Well they're meant to, but you can see them flickering, especially at the lower quarter of brightness. Or maybe I have better eyesight than the designers?
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To run a 5kV magnetron from 240V.

Microwaves do not penetrate all the way through larger volumes of food - the heating is done in the outer 1-2cm. Heating the middle is done by conduction (and by convection if the food is a fluid). If you pile in energy faster than it can conduct all the way through, you will have a burned outside and a cold middle.
Domestic microwave food products are not designed to be heated in 2kW ovens. Many would fail to cook properly/safely. Commercial microwave food products (some anyway) are designed to be heated in 2kW microwaves.
And in reference to your other post, it's not simply a matter of dividing the cooking time by two. The amount of energy absorbed by a food product also depends on the surface area exposed to the microwaves (1 pea in a 2kW oven will not absord 2kW), so the cooking time in a 2kW oven depends on the size and shape of the item - it would have to be calculated by the manufacturer and included on the packaging, but in practice, most domestic food products will not have sufficient heat conduction to be able to absord 2kW and cook properly.
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Andrew Gabriel
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That could be done with a transformer, with a few tappings to allow lower power.

I never have that problem, water (which most foods are primarily made of) conducts pretty quick.

Most meals are way bigger than a pea. Everything I cook is in a dish and about 1 inch deep. I'm sure that most if it would be hit by microwaves directly.
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wrote:

Because that's how it works.

As usual, you are so stupid that you havent even noticed that most words have more than one meaning.
https://en.wikipedia.org/wiki/Microwave_oven
In most ovens, the magnetron is driven by a linear transformer which can only feasibly be switched completely on or off. (One variant of the GE Spacemaker had two taps on the transformer primary, for high and low power modes.) Usually choice of power level doesn't affect intensity of the microwave radiation; instead, the magnetron is cycled on and off every few seconds, thus altering the large scale duty cycle. Newer models use inverter power supplies that use pulse-width modulation to provide effectively continuous heating at reduced power settings, so that foods are heated more evenly at a given power level and can be heated more quickly without being damaged by uneven heating.

Yeah, you know it all, no microwave designer knows anything.
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On 12/29/2018 10:16 AM, William Gothberg wrote:

There's been a lot of nitpicking in this thread.
All microwaves reduce power by cycling between 0 and 100% power. The relative power level is the duty factor of that on/off cycle.
Older microwaves switch the INPUT to the power transformer. That also runs the filament. The time to heat up the filament is the limiting factor in how short you can make the on-time. You get a minimum of about 10 seconds on-time. That minimum time is plenty to make food explode.
Better microwaves are called "Inverter" microwaves. I believe they're all licensed from Panasonic. When I bought mine, it seemed that all the licensees had dried up leaving Panasonic as the only locally available units.
It's my understanding that they heat the filament independently and can have very short on-times. Duty factor is the same as the older microwaves, but the on-time can be much shorter.
Foods don't explode on low power like they used to.
Food is not uniform. The effectiveness of microwaves decreases as the food thickness increases. There's a thermal time constant. So, if you cook at lower average power for longer time, you can warm the inside without seriously overcooking the outside or having local boiling that makes food explode.
The minimum on-time really helps with that. I haven't had food explode since I got an Inverter microwave. The defrost cycle really does work well.
They're slightly more expensive, but it's worth it.
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I've never exploded food on a non-invertor microwave. Maybe I don't cook thick enough stuff. Or maybe they should work more on making the microwaves more even so you don't get so many hotspots.
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