• ** REMEMBER! **The microwave can still shock you even unplugged!!

    ALWAYS discharge the high-voltage capacitor first if you even think your hands will come close to any HIGH VOLTAGE components.

    Jeff mentions this: Anything in the high voltage ( magnetron, capacitor, diode, wires to and from ):
    ...Use a metal ( not the shiny chrome type ) screw driver with a insulated handle to short across ( touch both at the same time ) the terminals of the high voltage capacitor to discharge it.

    From Jeff's site: http://www.applianceaid.com/component-testing.php

    Jake

Current draw

edf

Premium Member
Joined
Dec 20, 2010
Messages
22
Location
US
Model Number
401.85042210
Brand
Sears Kenmore
Age
1-5 years
The rating plate on our microwave rates the appliance at 15A. When I measure the current draw with a Kill-A-Watt device, the current draw exceeds 15A. Since the Kill-A-Watt is only able to measure up to 15A, I can only say it is over 15A (it beeps), but not how much. The microwave is on a 15A breaker, but the breaker does not pop.

Is this normal behavior for a microwave, or do they normally operate comfortably below their nameplate current rating?

Btw, this is what I mean by a kill-a-watt: Kill A Watt Meter - Electricity Usage Monitor | P3 ( Kill A Watt Meter - Electricity Usage Monitor | P3 )

I posted this yesterday,but it never showed up. Sorry if it shows up twice.
 

jeff1

Appliance Tech - Moderator
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Ontario, Canada
Hi,

The microwave is on a 15A breaker, but the breaker does not pop.
The instructions say to hook up a 20 amp service to the microwave.

The power supply cord and plug should be brought to a separate 20 ampere branch circuit single grounded outlet. The outlet box
How long did you test with the meter?
-Some- microwaves give more power for the first 1-2 minutes ( most of us just heat things up ) and then the power slows down a little if you are cooking in it for longer periods of time. So having a 15 amp reading at the beginning is likely normal....most are probably 12-14 amps approx.

jeff.
 

edf

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Messages
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Location
US
Hi,
The instructions say to hook up a 20 amp service to the microwave.
Wow. You're right. I assumed it would be 15A service, given the nameplate rating. I just double checked and the nameplate is actually 13.5A. Ahhhh. I see. 13.5A actual current, but derate the circuit 80% and you get 17A, so it has to be a 20A circuit. Ta da. Okay, that's easy to handle (it's a 12 gauge dedicated home run).

How long did you test with the meter?
-Some- microwaves give more power for the first 1-2 minutes ( most of us just heat things up ) and then the power slows down a little if you are cooking in it for longer periods of time. So having a 15 amp reading at the beginning is likely normal....most are probably 12-14 amps approx.
jeff.
Probably just a minute. It was long enough that I saw the current drop to around an amp or so when the oven went to the lower power part of the cycle, then back up over 15. It seemed as if it was cycling between applying microwave power and just spinning the turntable and that it would be over 15A any time it was delivering heating.

I can try again. I should have tried setting to a lower power, too.

I guess I skipped all that because it did not seem like a device should ever draw more current than what is stamped on the nameplate (even if the manual does say to put it on a 20A circuit). Is that not correct, then? We have a device stamped 13.5A, but it's drawing over 15A. Of course, the kill-a-wat may not be the most accurate thing....
 

jeff1

Appliance Tech - Moderator
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I guess I skipped all that because it did not seem like a device should ever draw more current than what is stamped on the nameplate (even if the manual does say to put it on a 20A circuit). Is that not correct, then?
You are correct, normally speaking it shouldn't use more than the tag....tag may be off a little, meter could be off a little, etc, etc.

jeff.
 

edf

Premium Member
Joined
Dec 20, 2010
Messages
22
Location
US
more info

I can try again. I should have tried setting to a lower power, too.
I tried again. During a "frozen vegetable" setting, which ran for a few minutes, it immediately went above 15A and stayed there throughout.

For a one minute 60% power run, it alternates between drawing over 15A and drawing 0.6A. When drawing the higher current, the microwave hums gently to moderately and when drawing the lower current, I just hear fan, turntables, and so forth. The 15A portions are around 15 seconds long and the low current portions are around 10 seconds long.

For a one minute 10% power run, it's the same story, but the 15A portions are much briefer, about 3 seconds followed by around 25 to 30 seconds of low power.

It seems like this oven either delivers full power, at which time it draws over 15A, or it draws only 0.6 A. It seems "low power" cycles on this machine aren't low power, but are just full power applied less often. Is that how microwaves usually work?

I also noticed that the kill-a-watt shows 15.3, 15.2, etc., i.e., it isn't just locked at 15 even (the limit for the meter), so maybe we're past the rated limit for the kill-a-watt, but it's telling us it isn't much past 15. In any case, 15 is just 10% over the 13.5 A nameplate.

If microwaves work this way- cycling between full power and being minimal power, then probably everything's okay and 90% agreement is reasonable?
 

jeff1

Appliance Tech - Moderator
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It seems like this oven either delivers full power, at which time it draws over 15A, or it draws only 0.6 A. It seems "low power" cycles on this machine aren't low power, but are just full power applied less often. Is that how microwaves usually work?
On manual settings ( reheating on high ) the power level would stay on high for the whole time selected.
On manual settings you can also select a lower power level ( EG: 50% or medium ) and the high power draw will be on 50% of the time and off 50% of the time )...high power 50% of the time, very low power 50% of the time.
On auto settings like pizza, soup, beverage, veggies, etc the power off and on is pre-programed and will cycle on and off at certain times or be on fully at certain times.

Some newer microwaves use an inverter board which is different.
100% is high power all of the time.
50% or medium would not be high power 50% of the time, very low power 50% of the time....it would actually give 50% cooking power 100% of the time.

Yours is the first style.
Hope this helps.

jeff.
 
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