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I recently took apart a microwave, and I managed to get a magnetron out of it, as well as a transformer that appears to be the power source for the magnetron, but looks a little small for the advertised amount of power this magnetron can handle (~1 kW). Also, the magnetron does not have any leads for supplying the filament voltage, just for the HV. I would like to get that magnetron running, I plan to put on a waveguide and do a bit of experimentation with microwaves.

1) Does the magnetron have something built in to step down a fraction of the power recieved to the 3.3V required to heat the filament?

2) Is it possible to run the magnetron simply by powering the microwave transformer with mains and hooking up the hv output to the input of the magnetron, or do I need a microwave capacitor? I was not able to locate a capacitor in the microwave, I think that might be because it is an inverter-style microwave.

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    \$\begingroup\$ darwinawards.com \$\endgroup\$ – EM Fields Sep 15 '14 at 0:25
  • \$\begingroup\$ If you are saying what I think you are, then my response is: There was not an HV capacitor in this microwave, like I said it is an inverter-style which at least in this case appears to use transistors to regulate power instead of an HV cap. I have taken apart another microwave before this one and seen the capacitor, so I know what they look like and would not be dumb enough to touch one (hopefully). Also, this microwave has not been in operation for quite some time, and so the cap would have discharged long by now, especially if it had a bleeder resistor. \$\endgroup\$ – user16871 Sep 15 '14 at 0:56
  • \$\begingroup\$ @user16871, OK sorry I'll delete my comment. Do be careful though. \$\endgroup\$ – George Herold Sep 15 '14 at 13:51
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    \$\begingroup\$ You do realize, that when I can buy one for 70 dollars in the store, that the manufacturer has already answered your question. \$\endgroup\$ – gbarry Nov 14 '14 at 17:52
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I believe the way microwave oven magnetrons are wired is that there are two coils on the transformer more or less in series, one to supply the HV and one to supply filament. The filament doubles as the cathode and it has some series inductors to keep the RF from leaking out the power terminals. The HV return from the anode could just be the metal case as it is less than an amp. An inverter-driven microwave likely has the same setup, however the transformer will be smaller as the switching frequency will be much higher (60 Hz vs several kHz). The inverter should have essentially the same connection to the magnetron as the older style single transformer solution. Also, you won't be able to run the inverter transformer by itself, you'll also need the rest of the inverter drive and control electronics. I'm not sure if it will work without the front panel/user interface; it may be required to turn the inverter on and possibly select the power level in some way.

However, turning on a magnetron outside of a case is very dangerous. Not only could you kill yourself with the high voltage, the high power microwaves could give you serious burns as well as possibly causing interference and damage to electronic deivces. The magnetron could also overheat due to reflected power if it is not properly coupled to a waveguide.

Edit: Looks like the inverter microwaves operate on exactly the same principle as the older ones, just at a much higher frequency. You'll either need to keep the front panel or figure out what signal it sends to the inverter to turn it on.

Panasonic inverter schematic

Image from http://www.electronicspoint.com/threads/microwave-inverter.234684/

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Acknowledging that this is an old question...

1) Does the magnetron have something built in to step down a fraction of the power recieved to the 3.3V required to heat the filament?

Yes. On the bottom of the magnetron, just below the input terminals, there is usually a square crimped-on cover. With that cover removed you should see two heavy gauge leads that run to a pair of fat RF chokes. These change the HV pulses from the power supply into the DC required for the filament heater.

2) Is it possible to run the magnetron simply by powering the microwave transformer with mains and hooking up the hv output to the input of the magnetron, or do I need a microwave capacitor? I was not able to locate a capacitor in the microwave, I think that might be because it is an inverter-style microwave.

No. The transformer alone will not reach the voltage required to drive the magnetron. Additionally, the transformer outputs AC power. Connecting unrectified AC to the magnetron will very likely destroy it and/or the transformer in very short order.

This link can answer many of your questions. Do be careful, an operating magnetron is like a 1,000 Watt Lightbulb. Close up or as a directed beam it can burn you and make you blind faster than you can blink. Additionally, it can destroy electronics at obscene distances. I have yet to see one equipped with an undo button.

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