Inverter Microwave - Current Draw vs. Power Setting

There should be a plateau minimum somewhere down in the power range. Just like a stereo with the volume turned off. My 1875 watt commercial microwave (20 amp plug) draws a disproportionate amount of energy and it's not modulated it's simply timer variable on-off. I laughingly refer to it as "555 control"

I did a test with a killowatt meter years ago when I installed a panasonic true inverter mw. Besides doing a MUCH better job of cooking at lower power, yes, current draw is reasonably linear with power setting. On mine 50% power draws 800VA, just perfect to run from my 1000VA true sine inverter. draw keeps dropping all the way to 10% and I didn't see any cycling jumps in power below 30% as others have mentioned, but at the low power level, the constant draw from the rest of the electronics comes into play and at 10% power IIRC it still drew aroun 25% of full rated power.

I tried one Panasonic "inverter" microwave model on MSW and it wouldn't run at all. If you're using MSW you might want to check that out before committing to a plan.

You're Welcome!
Glad I could help.

Boon Docker wrote:
Just did a test on my inverter mic and at full power it draws 16 amps. At 50% power it draws 8 amps. Tested with a Kill A WATT meter.

Thank you for taking the time to do this test, Boondocker! Wanted to get a confirmation that there was a corresponding reduction in current when the power level was reduced. My wife prefers the way an inverter microwave cooks and defrosts, so looking to replace the unit in our camper. The unit we were looking at draws a bit more current than I'd like (at 100%). Just wanted to make sure we could reduce the power/current level to accommodate our inverter if need be. Thanks again.

You are right about the lower setting. Below 30% power the magnetron does cycle on and off according to the KILL A WATT meter.

Inverter microwaves do indeed have their (peak) current draw change when the cooking power changes, down to some value (maybe 30 or 50% power). Below that level, they cycle on and off at the lower power setting similar to standard microwaves.

For this reason they're especially useful with inverters; by lowering the peak power draw, you can get better battery life thanks to operating in a better part of the peukert equation.

(Internally, inverter microwaves basically just use a switching power supply, with a switching frequency of ca. 20-40 kHz, rather than a 60Hz transformer to generate the high voltage needed for the magnetron. There are some details and constraints that make it not a run-of-the-mill switching power supply, but that's the basic concept. As such, they should be pretty well immune to line voltage changes and operate efficiently at full power with MSW inverters.)

Gdetrailer wrote:

BFL13 wrote:
One of the guys here posted about his Panasonic MW that pulls less power with lower settings. A "normal" MW draws full power when on, but at lower settings is not "on" as much.

A MSW inverter will draw less from the battery bank than a PSW inverter with a MW as load, but it takes longer to "cook" something. Even so, I found the MSW draws fewer AH doing that because the Amps component is bigger than the Hours component.

Also a potato is "ready" when you stick a knife in it, and how soft you want it is subjective, and it softens more after you take it out of the MW, so just when is a potato "done" anyway?

Also with things you have to cool down before you can eat them. Why get them so hot?

Some older MWs like the one in our 1991 C will not run on MSW so you need a PSW inverter anyway. MWs since at least 2003 (as in our 5er we had) run ok on MSW. You do need a MSW inverter that is rated to run motors though. They can do a MW.

Standard MWs use a PWM method when you set the power level lower than 100% basically changing the duty cycle to control power level.

Basically the average power is lower during the MW operation.

They vary the time ON vs Time OFF and when ON, the magnetron is at full wattage.

Example, 90% power level and the magnetron is ON 90% of the time and 10% OFF of the time.

50% setting magnetron is ON 50% and OFF 50%.

Boondocker has said that they see half the current draw at 50% with their Inverter MW which means the inverter type are not using full on power, so they must be lowering the magntrons input voltage to lower the output.

Interesting..

From what I understand this is the way it operates.

BFL13 wrote:
One of the guys here posted about his Panasonic MW that pulls less power with lower settings. A "normal" MW draws full power when on, but at lower settings is not "on" as much.

A MSW inverter will draw less from the battery bank than a PSW inverter with a MW as load, but it takes longer to "cook" something. Even so, I found the MSW draws fewer AH doing that because the Amps component is bigger than the Hours component.

Also a potato is "ready" when you stick a knife in it, and how soft you want it is subjective, and it softens more after you take it out of the MW, so just when is a potato "done" anyway?

Also with things you have to cool down before you can eat them. Why get them so hot?

Some older MWs like the one in our 1991 C will not run on MSW so you need a PSW inverter anyway. MWs since at least 2003 (as in our 5er we had) run ok on MSW. You do need a MSW inverter that is rated to run motors though. They can do a MW.

Standard MWs use a PWM method when you set the power level lower than 100% basically changing the duty cycle to control power level.

Basically the average power is lower during the MW operation.

They vary the time ON vs Time OFF and when ON, the magnetron is at full wattage.

Example, 90% power level and the magnetron is ON 90% of the time and 10% OFF of the time.

50% setting magnetron is ON 50% and OFF 50%.

Boondocker has said that they see half the current draw at 50% with their Inverter MW which means the inverter type are not using full on power, so they must be lowering the magntrons input voltage to lower the output.

Interesting..

One of the guys here posted about his Panasonic MW that pulls less power with lower settings. A "normal" MW draws full power when on, but at lower settings is not "on" as much.

A MSW inverter will draw less from the battery bank than a PSW inverter with a MW as load, but it takes longer to "cook" something. Even so, I found the MSW draws fewer AH doing that because the Amps component is bigger than the Hours component.

Also a potato is "ready" when you stick a knife in it, and how soft you want it is subjective, and it softens more after you take it out of the MW, so just when is a potato "done" anyway?

Also with things you have to cool down before you can eat them. Why get them so hot?

Some older MWs like the one in our 1991 C will not run on MSW so you need a PSW inverter anyway. MWs since at least 2003 (as in our 5er we had) run ok on MSW. You do need a MSW inverter that is rated to run motors though. They can do a MW.