Microwave heating, two 30 second cycles don't equal one 60 second

Discussion in 'General Electronics Chat' started by jmoffat, Aug 24, 2016.

  1. jmoffat

    Thread Starter Member

    Jul 18, 2012
    My casual observation (no actual measuring instruments have been harmed in any way) is that food or beverage placed in the microwave doesn't get as hot when the 30 second heating cycle is used twice compared to when the 60 second cycle is selected. Is this possible? Why?
  2. crutschow


    Mar 14, 2008
    There may be a small delay between the start of the time period and the actual output from the microwave magnetron (on my microwave you can tell by the sound).
    If you do two cycles, then you would get two delays instead of one.
  3. tcmtech

    Distinguished Member

    Nov 4, 2013
    A magnetron is still a vacuum tube and like any vacuum tube it has a heating element inside it that needs to get things up to temperature before it produces any output.

    Figure 5 - 10 seconds to get things up and going before any microwaves of high enough energy to cook food are being produced.
    Aleph(0) likes this.
  4. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
    Yep, totally true. the magnetron doesn't instantly heat,

    If you phase angle fire for power, then the sine wave timing won;t be linear. You can use the RMS of V or the RMS of V^2 vs phase angle.
  5. Aleph(0)

    Active Member

    Mar 14, 2015
    Yupper! it can take 7 seconds for 2M series magnetron filament to be up to full emission, even longer if appliance totally shuts filament current off when standing by:cool:
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  6. tcmtech

    Distinguished Member

    Nov 4, 2013
    Highly likely being most every microwave oven I have ever scrapped out had the magnetron heater driven off the same transformer that made its HV so there was no independent preheat/standby heater circuits in play.
    Hypatia's Protege likes this.