The only thing I know about inverters is that they convert DC into AC. But I've come across the term before and am curios to exactly what's going on. For instance, my MIL (Mother-In-Law) has a washing machine with an "Inverter" type motor. I know NOTHING about what that is, other than it is used to spin the drum or agitate the clothing. The way it works is the motor reverses direction. I know that to be contrary to good practices with motors as they don't like slamming back and forth. Still, this is what I have heard of.

Also, in another thread someone was asking about reducing power to a microwave oven. The comment was made by @MrAl: "...I got a Panasonic oven that has 'inverter technology'..." and I'm wondering what other ways inverters are being used.

 

Your M-I-L's W.M. most likely has a Fisher Paykel out-runner motor, they do not use a gear box as the older style did. The outer rotor is attached to the drum.
It is three phase - electronically produced.
https://www.fisherpaykeltechnologies.com/
Max.

 

Thanks @MaxHeadRoom. I'm more interested in learning what other ways "Inverter Technology" is being applied. @MrAl mentioned purchasing a microwave with Inv. Tech. Immediately started wondering exactly what that means? My three microwaves all have a feature where you can defrost meat. The problem is when you defrost, because the rotary plate spins at 6 RPM (one revolution every 10 seconds) when defrosting - the oven heats at full power for (lets say) half the time, meaning the food is typically in the same place when the heating occurs. This results in parts that are still frozen and other parts that are beginning to cook prematurely. I think an oven with an adjustable output (for cooking) would be marvelous. I don't know if such things exist.

Anyway, I'm more interested in learning something new than trying to solve any problems at this point.

But thanks for the reply. Always appreciated.

 

Thanks @MaxHeadRoom. I'm more interested in learning what other ways "Inverter Technology" is being applied. @MrAl mentioned purchasing a microwave with Inv. Tech. Immediately started wondering exactly what that means? My three microwaves all have a feature where you can defrost meat. The problem is when you defrost, because the rotary plate spins at 6 RPM (one revolution every 10 seconds) when defrosting - the oven heats at full power for (lets say) half the time, meaning the food is typically in the same place when the heating occurs. This results in parts that are still frozen and other parts that are beginning to cook prematurely. I think an oven with an adjustable output (for cooking) would be marvelous. I don't know if such things exist.

Anyway, I'm more interested in learning something new than trying to solve any problems at this point.

But thanks for the reply. Always appreciated.

Hi,

Inverter Technology for a microwave oven essentially means that it actually turns the power down not pulse it.
In a normal 1000watt oven, for 50 percent power it might pulse on for 10 seconds and off for 10 seconds, then repeat.
In an inverter 1000 watt oven, it just turns the total output power down to 500 watts and is always 'on' never 'off'.

What a general converter/inverter does is it takes in say 120vac and puts out whatever you adjust it for, like 100vac, 90vac, whatever.
So the inverter microwave oven just lowers the input power so the oven cooks more slowly and evenly.

Using the Variac, i just turn the voltage down to whatever gives me a certain input power like maybe 600 watts instead of the full 1500 watts.
So i get slower cooking without having it pulse on and off.

Converters/Inverters are used in various places for various things.
One use is to convert DC to AC of course.
Another is to convert one type of AC to another type, either voltage or frequency or both.
A very common use in industry is to use one to 'regulate' the output voltage despite what the input voltage is. In most parts of the country the line can vary from about 90 to 130vac, and of you want a constant 120vac then one way is to use a converter because you can adjust it for 120vac and it will stay constant (as long as that is part of the design).
Another use so to change the frequency. I've seen them go from 50 to 60 Hz and from 50/60Hz to 400Hz for aircraft.

 

@MrAl mentioned purchasing a microwave with Inv. Tech. Immediately started wondering exactly what that means?

According to Wikipedia "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".

 

So then (theoretically - or maybe factually) an inverter can be used something like a variac. Yes? No?

 

Although a Variac does not 'convert' as such, just a variable linear controller.
Max.

 

One other example of an invertor as used in your in-laws WM is a VFD.
Max.

 

I know nothing about VFD's (other than Variable Frequency Drive) (if that's even correct).

 

Yes the inverter stage takes HV DC and converts to variable 3ph AC, usually via a 'inverter' IGBT switching output stage.
Max.

 

One interesting thing about 3-phase is that the combined power output of the 3-phases is constant.
There is a fluctuation of the voltages, of course, but the power is constant.
That's why 3-phase motors are quieter and more efficient than single-phase motors.

 

Varying the input of a inverter microwave oven to try to control power does not provide good control and may damage the oven. The pulse width modulation provides better control of power level. I don't understand why anyone would try to take a less efficient means when a better method is already in use.

I am a former microwave oven engineer from the pre-inverter days but recognize the utility of the inverter circuit since I also designed SMPS after I left the microwave oven industry. The inverter circuit is definitely superior to the voltage doubler circuit we had in the 80s.

@Tonyr1084 The microwave energy distribution in the oven is very complex and the food being in the same place while the oven is on doesn't cause as much of an issue are you suppose. Just moving the food a little can substantially change the energy distribution pattern. You might get better distribution by setting the food off center so that the microwave energy pattern is more varied.

 

You might get better distribution by setting the food off center so that the microwave energy pattern is more varied.

Don't the ovens these days include 'mode stirrers' to distribute the energy more evenly; or is that old school?

 

Varying the input of a inverter microwave oven to try to control power does not provide good control and may damage the oven. The pulse width modulation provides better control of power level. I don't understand why anyone would try to take a less efficient means when a better method is already in use.

I am a former microwave oven engineer from the pre-inverter days but recognize the utility of the inverter circuit since I also designed SMPS after I left the microwave oven industry. The inverter circuit is definitely superior to the voltage doubler circuit we had in the 80s.

@Tonyr1084 The microwave energy distribution in the oven is very complex and the food being in the same place while the oven is on doesn't cause as much of an issue are you suppose. Just moving the food a little can substantially change the energy distribution pattern. You might get better distribution by setting the food off center so that the microwave energy pattern is more varied.

Hello there,

You dont understand probably because you did not read this whole thread before you replied.

First, no one is trying to vary the input power to an already inverter type microwave oven. The input power vary method was being used for NON inverter ovens only. That turns a pulsing on/off type controlled oven into a smooth variable power controlled oven. So we start out with a regular non inverter oven and set it on HIGH, then use the Variac on the input to change the power level in a continuous manner rather than a slow pulse manner.

We know there are inverter type ovens, but they are more expensive than the cheap run of the mill non inverter ovens. So if you have a variac you can use it on a regular oven and get smooth power level settings.

If you worked in this industry then maybe you can tell us more.

 

Don't the ovens these days include 'mode stirrers' to distribute the energy more evenly; or is that old school?

Hi,

Some of them do, some of them dont. Mine does not and it was a higher priced inverter type oven.

 

The ones I have use the carousel method. Some I've scrapped had a small aluminum plate (I think it was aluminum) also on a gear driven motor that would (as I suppose) redirect the MW energy to distribute a more even heating. I haven't pulled mine apart yet, but I do notice a few issues: First the food still seldom cooks evenly. I can still scald my tongue with one bite then sooth it with the next, still cold, some cases icy bite. The second issue is that when on the defrost cycle it will cook, as I believe @crutschow said, on for (for example) five seconds, off for five seconds (on/off depends on percentage level chosen). This will cause part of the food to begin cooking prematurely while other parts are still frozen solid.

If there are better ovens then I'm up for buying one for over the stove and installing it. While at it I may choose to vent the cooking fumes outside as opposed to sending them up over head into the room. Someone needs to invent a smoke alarm that automatically shuts off when the wife yells "I'M JUST COOKING!" (from the jokes thread, someone else joke, not mine).

 

You might get better distribution by setting the food off center so that the microwave energy pattern is more varied.

I do that. Gets better results, but sometimes food is just so large it must be somewhat centered. And I still get cold spots and nuclear summer spots.

[edit]
BTW; this is not about microwave ovens. I was asking about the use of the term "Inverter Technology". To me it seemed like more than just the inverters I know of from 12 volt inverters, UPS and solar inverters.
[end edit]

 

"inverter technology" is a buzz word. Marketing has to use something.

For microwave ovens, you get more uniform heating, not On and OFF cycles. The filament takes time to warmup.

For motors, lets call it, Electrically Commutated Motors. It might generate 3 or 6 phases electronically. No brishes.
the cool part is energy efficiency. the other cool part, you get RPM. Apparently within a system, its capable of measuring static pressure and CFM and operating at an infinately variable speed.

Had amotor at work that ran at 40,000 RPM.

House thermostat shows CFM, static pressure and RPM.

This: www.icemeister.net/Articles/ECM_Motors.doc might help.

 

So, as I've learned today, in some cases an inverter is used to convert AC to DC then back to AC at a different frequency. OK. Got it. At first I thought it might be some alien technology stolen from Roswell or Area Fifty-One.

 

Tony, I have wondered the same thing. I think the use of the term comes from the use of the term converter.

In the olden days, most electronic apps, used DC. And a power supply would convert AC line V into DC voltage.

So originally to invert, would be to convert DC back into AC. Or a Power Inverter. Such as powering tube equipment from batteries.

We now have the tech, to control AC very precisely from a DC bus. In amplitude, frequency, phase and duty cycle. Lot's of parameters to work with.

Now, establishing and controlling these AC parameters could be called inverting.

Right now, one use of this is for our old motor tech. But as seen, now we are building new types of motors, to take advantage of the control techniques. Motor technology has a bright future.

Of course "inverters" doesn't just apply to motor tech. It's great for regulation and control for many apps.

That's my take. The word has a more general meaning now.

Now, I don't get out much, my opinion might be out-dated.