On Sun, 30 Dec 2018 05:47:48 -0000, Johnny B Good wrote:

On Sat, 29 Dec 2018 13:23:55 -0800, mike wrote:

On 12/29/2018 10:16 AM, William Gothberg wrote:
On Sat, 29 Dec 2018 17:38:04 -0000, Clare Snyder
wrote:

On Sat, 29 Dec 2018 08:07:42 -0800, Bob F wrote:

On 12/29/2018 6:37 AM, trader_4 wrote:
On Saturday, December 29, 2018 at 9:23:42 AM UTC-5, Bill Gill wrote:
On 12/29/2018 7:43 AM, William Gothberg wrote:
Shouldn't we have faster microwaves by now giving out a few kW?
They were invented decades ago.
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

+1

That about covers it. Not sure how useful more power would be. For
example,
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.


It gets the 30% power by cycling the 100% power on 30% of the time.

(By the way, adjusting the level does not actually change the
wattage.
It simply means the microwave will pulse on and off at its fixed
wattage until the desired level is reached.)

https://lifehacker.com/5974788/famil...elf-with-your-
microwaves-power-settings-to-make-microwave-cooking-a-joy

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)

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!

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.

I knew the inverter types could still only rely upon variable duty cycle
heating control like the earlier voltage doubling HT transformer/
rectifier/HV capacitor designs did. I just wasn't quite sure what the
benefit of an inverter over a simple voltage doubling circuit was until
you let on about the cathode heater/filament being able to remain fully
powered throughout the whole cycling period.

This 'cathode filament/heater always on' aspect isn't the only benefit
of an inverter type allowing a higher cycling frequency to be employed,
it also provides a well regulated HT voltage, free of the 50/60 Hz ripple
which spoils the efficiency of the magnetron in the older designs.

The HT voltage (and anode current - no longer affected by heating/
cooling cycles imposed upon the cathode) has to be kept to within a
fairly tight tolerance (by the standards typical of domestic white goods)
for optimum operation at the correct microwave frequencies.

The effect of changing anode voltage is analogous to the effect of how
hard you blow across the open top of a beer bottle (empty or partially
empty) to generate a musical tone. The stronger you blow, the higher the
sudden jump in pitch will be. The microwave frequency produced by a
magnetron is likewise affected by how strong a voltage is applied to its
anode and will jump in frequency just like a blown beer bottle and for
exactly the same analogous reason (electrons rather than air molecules
being involved in this case).

In short, the only way to control the power output of a magnetron
without detuning it from its optimum 'microwaving' frequency is by using
variable duty on/off cycling. There's no smooth continuous analogue power
control option in this case.

As for those large 2 and 3 KW microwave ovens used in commercial
kitchens, they use a much larger cooking cavity so that a bunch of "Five
Minute Meals" can be heated concurrently in the recommended 5 minutes
rather than be processed in batches of just one or two at a time.

The microwave energy doesn't magically focus in the deep interior of the
food and heat it from the inside outwards. The microwaves only penetrate
the first centimetre or two before losing sufficient of their energy in
this process so as to have insignificant effect on the deeper interior
which therefore relies upon conduction from the hotter outer portions to
raise its temperature sufficiently to kill any pathogenic micro-organisms
so as to eliminate the risk of food poisoning.

Can we not have a different frequency which goes deeper before being absorbed? Or even a combination of more than one frequency? Or a choice depending on the food you're cooking?

This, as has already been pointed out, takes time and, surprise
surprise, doubling the rate at which microwave energy is being poured
into the outer layers of the foodstuff in question, does not halve the
time required to complete the cooking process.

Indeed, as has also been pointed out, such an increased rate of energy
input will tend to overheat the outer layers so much so as to overcook
them. The increased temperature will simply result in a higher rate of
radiative and convective heat loss back into the cooking cavity with
rather less than you may have imagined making any useful contribution to
raising the deep interior temperature of the foodstuff in question.

Depends what you're cooking/heating in there. If I put in a large bowl of vegetables in cold water, it takes quite a while to get to boiling point before the veg starts to cook. And since it's chopped veg in water, everything gets heated, nothing is more than a cm deep. Doubling the power would heat them up way faster.