May 28th, 2013
All microwave ovens work the same. But do you know how they work? Where did they come from?
Each and every Microwave oven has four basic parts that consist of a (Very) High Voltage Source (Transformer), A (Very) High Voltage Capacitor, a Diode (or rectifier) and a Magnetron Tube. These Four items make up the HIGH SIDE, and if any one of these four items fail, the microwave won’t heat. Of course, there are other causes for failures but are all located on the LOW SIDE, which I’ll get into later.
To make a Microwave Oven work, ordinary house voltage (120 VAC) is fed into the Primary Winding of the Transformer. This 120 VAC or Alternating Current, reverses itself 60 times each second (in the USA–Elsewhere its 50). Those of you who have had basic physics or electricity know that Alternating Current produces an expanding and contracting magnetic field, and is the reason so much can be done with AC Voltage, and why Edison’s Direct Current technology was never adopted for widespread use in the U.S.
This “alternating” magnetic field flowing through the Primary windings of the Transformer “cuts” (by magnetic induction) across the windings of the Transformer’s Secondary Windings, (which has many, many more windings than the primary) and “induces” a voltage in them. (A winding is nothing more than a single turn of copper wire “wound” around and iron core). The more windings in the secondary the higher the voltage will be in that winding.
The POWER remains the same, because you cannot eliminate energy, only convert it, but that’s an other story…
So now the 120 VAC in the Primary winding has been “transformed” into roughly 2500 volts. That’s a lot of energy- but we’re not through yet. As high as that voltage is, its STILL NOT ENOUGH to activate the Magnetron Tube.
So we need a VOLTAGE DOUBLER. That’s where the Capacitor and Diode come in. Now, the Secondary Winding with its 2500 volts charges the Capacitor in ONE direction (remember, AC voltage goes two ways, or ALTERNATES. The Diode on the other side of a Capacitor allows current to flow in one direction only. That’s what Diodes do. So, the Diode allows current to charge the capacitor in one direction and blocks current in the other direction which essentially “PUMPS UP” the capacitor to TWICE the voltage being applied to it via the Transformer Secondary. You see, without that Diode on the Capacitor there- the AC current (from the transformer) would alternately charge the capacitor on both sides, resulting in equal charge on both sides or no voltage at all.
Nada, zip, zero, nix.
Don’t worry, it gets worse.
Ok, that leaves about 5000 volts at the capacitor ready to go to the Magnetron tube. Think of the MAG TUBE as an antenna, because that’s what it really is, a VERY HIGH VOLTAGE antenna that vibrates at about 4.5 Mega (Million) Hertz, or cycles. That 5000 volts pushes against that MAG TUBE antenna SO HARD that it starts to vibrate. Those 4.5 Mega hertz (or Mhz for shorthand) are what cooks your food, or more specifically whats causes the WATER MOLECULES in the food to vibrate about furiously, knocking into and colliding against each other- FRICTION, and THAT is what makes heat.
So that is essentially what makes a Microwave oven work. I’ve spent a lot of time writing about the HIGH SIDE, but what about the LOW SIDE?
Well, the Low side is nothing more than a timer, or some electronic control that switches on the 120 VAC that goes to the HIGH SIDE. All those fancy controls and electronics on your Microwave oven are essentially in the purest sense, a switch. That’s it. And of course a variety of safety devices in the form of door switches assures that the oven won’t ever operate with a door open, flooding the kitchen with Microwave energy. Also, the Door is designed specially too. Those screens on the door are sized very specifically so Microwaves will not pass through them. On all microwaves, the size of those screen holes is all the same.
So what about those Power Levels eh?
Remember the microwave control (or switch) just does ONE THING- its turns something ON and OFF. There are no varying levels of power going to the HIGH SIDE. Varying power is done by timing the on and off cycles to the High Side. Low power settings may mean the High Side is switched on for 10 seconds of every minute and conversely, high power would mean the high side switched on for one minute of every minute, and everything in-between.
Microwave cooking was discovered quite accidentally during WW2. Radar technicians adjusting the equipment noticed the Hershey bars in their pockets were melting. And from there, somebody got the idea of using those waves to cook. The first commercially available microwave oven was made in the 50′s by Amana, which was absorbed by Maytag, which was absorbed by Whirlpool. It was called (fittingly) the RADAR-RANGE.