Tom's Life Bits

The GE microwave has an inrush relay. I did some online googling to figure this thing out. I believe this is a Samsung controller and in my search I tripped across a Samsung patent for this inrush relay which gives some insight into the circuitry.

How It Works

From the GE wiring diagram, a relay labeled main relay, RY01, applies power to to the lamp, turntable and fan. An inrush relay applies power to the magnetron transformer through a thermistor. A third relay, Power Relay RY03 on the PCB, labeled Power Relay RY2 on the GE wiring diagram, has it's contacts wired to jumper the contacts and series thermistor of the inrush circuit. From the Samsung patent it mentions an inrush time of 30 to 40 MS. Based on this info, I have the following proposed operation:

1. Turn on the Main Relay, RY01.
2. Several milliseconds later turn on the inrush relay.
3. 30 to 40 MS later activate the Power Relay.
4. the inrush relay can now be de-activated

The magnetron activation needs to be a separate routine with the inrush control built in. This routine would activate inrush, wait 40 MS, turn on the power relay, wait 10 milliseconds, turn off inrush relay.

Duty cycle cycling of the magnetron would use the magnetron activation function to activate the magnetron periodically.

This design article proposes a time delay relay to limit inrush, very similar to what the GE microwave does.