Microwaves and Variable Power

[panamajack]

Why do microwave oven power settings have such long periods? As far as I can tell, most, if not all microwaves use a single tube of constant power, and switch it on and off depending on the selected power setting.

Firstly, I'm wondering if there's ever been a microwave oven that used a different method for reducing the power. If I had to guess, I'd think it was because it's far easier to design around one tube, or that the average power would still be too high if other schemes were used.

The thing I don't get is why the cycle is so long. On the one I just looked at the cycle is 30 seconds. Others seem to be similar. This seems crazy given that most items in a microwave are only there for 5 minutes or less. Does it really take that much time to warm up the tube, or is it just the tradition?

Also, do most microwaves still use a magnetron or do some now use solid-state emitters (which would make this problem go away)?

[mks57]

I think the long cycle is to avoid premature failure of the magnetron. Most vacuum tubes do not like being repeatedly turned on and off. It stresses the tube.

[Q.E.D.]

Yes, they still use a magnetron tube. Some higher-end ovens are capable of regulating the output power of the tube directly, rather than resort to controlling the duty cycle, but the circuitry to do this is more complicated and therefore more expensive.

[yoyodyne]

I have a Panasonic countertop that has a power inverter which changes the tube output instead of the cycle time. I think most of theirs do it that way.

[si_blakely]

Originally Posted by yoyodyne

I have a Panasonic countertop that has a power inverter which changes the tube output instead of the cycle time. I think most of theirs do it that way.

Yep, so the inverters seem to fail with astounding regularity. At least, that was my experience - three inverters over 4 years. Once all the extended cover ran out, I refused to get another Panasonic.

Si

[panamajack]

Thanks for the answers - I was thinking it might be a reliability/longevity issue.

Poking around I found that a solid state microwave oven was patented in 1971 US 3557333, with a few other innovations since then.

It seems odd that it's taken so long for any company to successfully market one (as far as I know).

I also see that the patent references a MTTF for magnetron tubes at 500 hours (back then at least). Did they just get a whole lot cheaper/better since then?

[yoyodyne]

Originally Posted by si_blakely

Yep, so the inverters seem to fail with astounding regularity. At least, that was my experience - three inverters over 4 years. Once all the extended cover ran out, I refused to get another Panasonic.

I've had mine for four years with no problems at all.