Hi,
Anyone have a (good!) idea as to what sort of load a microwave oven presents? I.e., how reactive/resistive?
Of course, all newer ovens tend to just be a single power level duty cycle modulated so you're always faced with the same
*peak* load. I'm just curious as to how much to derate an inverter for use with one...Thx,
--don
"Don Y"
** Resistive and close to a sine wave current draw.There is an inrush surge, but it's not enormous.
** The inverter will need to be rated at 2kW, have good sine wave output and the right frequency - 50 or 60 Hz.It must protect itself from overloads of 3 times or more.
Very few inverters are suitable for use with microwave ovens.
.... Phil
"Phil Allison"
** Here is one example, check out the videos.The 1500W models should do most microwaves.
... Phil
Given what little o know about magnetrons figure on full power, step up transformer, bridge rectifier onto into a massive capacitor with an otherwise resistive load with no more that 10% ripple. Inverter types may have PFC circuits which will be a much tamer load, but don't bet on it. So for a small 600 W oven i would want about 1.5 kW of inverter. Note that this will be anywhere from 50 to 120 A at 12 V.
But that is just my guess.
?-)
"josephkk"
** ROTFLTypical microwaves have one diode and one cap of less than 2uf in the PSU.
The Magnetron itself is the other diode and the PSU is resonant at the third harmonic.
Hence, the microwave energy is heavily modulated at supply frequency and the AC current draw is a reasonable sine wave.
.... Phil
From monitoring their splattering BURSTS of 2.45GHz, I would model most uWave ovens as being CHEAP. The magnetron only comes on once an AC cycle, not even full wave bridge, just a single diode into a cap, that then supplies the magnetron, with conduction angle somewhere between 10-20%. As a result, the interference is related to the AC mains frequency and 'splatters'. These two characteristics allow Bluetooth, Wifi, zigbee, other wireless to operate 'around' them.
If the uWave ovens are still made that way, that's a difficult load to drive from an inverter.
The classic circuit is a voltage doubler- the diode is in parallel with the magnetron and a HV cap in series with the xmfr, so the magnetron cathode and heater voltage swings something like +10V to -kV (anode is at ground).
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