Microwave Blues

Tombsl
Tombsl Registered Users Posts: 13 ✭✭
in Solar Beginners Corner #1
I have a 2000 watt inverter at my cabin, and tried to use a 1200 watt microwave with it. Even tho the maximum input to the microwave is rated at 1480 watts, the inverter shuts down when I turn it on. Is there something I'm missing about microwaves?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: Microwave Blues

    What size battery bank do you have (voltage/amphour)?

    Have you measured the DC input voltage to the AC inverter right at its input lugs when running the inverter (try a full size space heater as load if you need something adjustable to test your wiring/battery bank/inverter)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: Microwave Blues
    Tombsl wrote: »
    I have a 2000 watt inverter at my cabin, and tried to use a 1200 watt microwave with it. Even tho the maximum input to the microwave is rated at 1480 watts, the inverter shuts down when I turn it on. Is there something I'm missing about microwaves?

    It may not be the microwave that is the problem... What brand and model inverter? What do you have for batteries? --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Microwave Blues
    Tombsl wrote: »
    I have a 2000 watt inverter at my cabin, and tried to use a 1200 watt microwave with it. Even tho the maximum input to the microwave is rated at 1480 watts, the inverter shuts down when I turn it on. Is there something I'm missing about microwaves?

    A). Even though it says "1480 Watts" it may draw more (isn't that nice of them?)
    B). Concurrent loads add up on inverter.
    C). MSW type inverter will not 'like' a microwave, nor will the microwave 'like' MSW.
    D). Voltage sag on the DC side can be pretty high with such a load, especially on a 12 Volt system. This is wires, connections, and batteries.

    I have a "600 Watt" microwave. It pulls 1080 Watts. I have a 24 Volt system with over-sized wiring and a 232 Amp hour battery bank. I use it only on sunny days or when the gen is running. The system still 'feels' the 45-ish Amp draw.

    You would be looking at 124 Amps+ for that microwave on a 12 Volt system. That's a nasty amount of current.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #5
    Re: Microwave Blues

    Like the other posters, my first thought is DC voltage sag dropping below the inverter's low voltage shutdown point.
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  • Tombsl
    Tombsl Registered Users Posts: 13 ✭✭
    #6
    Re: Microwave Blues

    Thanks for the help. I think you are all correct -- the problem is that my system is too light (4 6V 420 ah batteries deivering 12 volts) to feed the microwave. The inverter is 2000w pure sine wave. I read a related article that points to the same issue. The learning continues !
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #7
    Re: Microwave Blues
    Tombsl wrote: »
    Thanks for the help. I think you are all correct -- the problem is that my system is too light (4 6V 420 ah batteries deivering 12 volts) to feed the microwave. The inverter is 2000w pure sine wave. I read a related article that points to the same issue. The learning continues !
    A 1,000 watt microwave will pull 110 or so DC amps. 6v deep cycle batteries are slow to give up that much current, you have to way oversize the cabling to 4/0 on the Inverter and battery interconnects. That said, 4 of them should run it, then again your Inverter might not be up to snuff.
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #8
    Re: Microwave Blues

    A typical microwave will draw much more than the rated input power on startup. An inverter based microwave (like some Panasonic models) reduces this, although I'd like to see more actual figures.

    I am available for custom hardware/firmware development

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  • Dragonlady5
    Dragonlady5 Registered Users Posts: 19 ✭✭
    #9
    Re: Microwave Blues
    Tombsl wrote: »
    I have a 2000 watt inverter at my cabin, and tried to use a 1200 watt microwave with it. Even tho the maximum input to the microwave is rated at 1480 watts, the inverter shuts down when I turn it on. Is there something I'm missing about microwaves?

    Yes, you are (missing something) but it's not your fault. It took some digging with Panasonic but here's "watts" up:

    At Power lever 10 the following current will be drawn for the time shown.
    Time (min) 1 2 3 4 5 7 10 (min)
    Input I (A) 17 16.7 16.5 16.2 15.7 14.9 14.7 (A)

    Notes: 17 Amp X 120 VAC = 2040 Watts
    Because this higher power is NOT "continuous" (3 hours) they do not have to put the higher rating on the label.

    I typically recommend an inverter be sized to 2 times the cooking Watts. Better to be save than overloaded.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #10
    Re: Microwave Blues
    Dragonlady5 wrote: »
    Notes: 17 Amp X 120 VAC = 2040 Watts

    That would be 2040 VA, not necessarily watts - - depending on power factor, but could still "appear" as a 2040 watt load to the inverters output circuits.
    On another note, it has been mentioned a number of times in different threads here over the years, that a traditional microwave oven has a relatively large start surge. Actually, with the exception of an initial blink of an eye spike which sometimes but not always occurs when power is first applied to the main transformer, which then settles down after 2 or 3 AC cycles of the 60 Hz supply, microwave ovens actually start out at quite reduced power consumption, which ramps up to full power as the cathode in the magnetron comes up to operating temperature, allowing the magnetron to begin conducting.
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  • Dragonlady5
    Dragonlady5 Registered Users Posts: 19 ✭✭
    #11
    Re: Microwave Blues
    waynefromnscanada wrote: »
    That would be 2040 VA, not necessarily watts - - depending on power factor, but could still "appear" as a 2040 watt load to the inverters output circuits.
    On another note, it has been mentioned a number of times in different threads here over the years, that a traditional microwave oven has a relatively large start surge. Actually, with the exception of an initial blink of an eye spike which sometimes but not always occurs when power is first applied to the main transformer, which then settles down after 2 or 3 AC cycles of the 60 Hz supply, microwave ovens actually start out at quite reduced power consumption, which ramps up to full power as the cathode in the magnetron comes up to operating temperature, allowing the magnetron to begin conducting.

    PF was relatively high so it was a wash between VA/W, and that wasn't the issue.

    I have not noted any significant start up surges in the relatively new Panasonic 1500 Watt (cooking) I looked at; when AC first applied (inrush), or when irradiation starts at power level 10. Perhaps older models have these characteristics.

    The answer: An inverter should be sized 2.5-3 times the cooking Watts.
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #12
    Re: Microwave Blues

    It would be interesting if people would publish startup waveforms for specific models. Easy to do with a clamp on current probe, a laptop audio input and "Soundcard Scope" software. The brief capacitor/transformer charging currents can sometimes be addressed with thermistors.

    I am available for custom hardware/firmware development

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  • Dragonlady5
    Dragonlady5 Registered Users Posts: 19 ✭✭
    #13
    Re: Microwave Blues

    I've been using the Picoscope for couple of years, my CRT based scope is gathering dust. Audio input and "sound card" somewhat crude but will work for general interest (scaling, detail, sampling issue I assume). I don't have the time to supply (other than what I have already) for customer interest as most would not understand anyway and make their decision on price not performance & proper sizing recommendations. IMHO.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #14
    Re: Microwave Blues

    Picoscope

    Hmmm, which one? their list is massive.

    Looks to be based in BC, US address is just a P.O. in Point Roberts, WA.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • Dragonlady5
    Dragonlady5 Registered Users Posts: 19 ✭✭
    #15
    Re: Microwave Blues

    The Picoscope product (picotech.com) is out of UK, suspect you are looking at something else in NA. You can purchase though Saelig. The software is the same for all the scopes, you choose the HW based on what you need channels, BW, sampling etc...
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  • opticalmike
    opticalmike Registered Users Posts: 20 ✭✭
    #16
    Re: Microwave Blues
    Tombsl wrote: »
    Thanks for the help. I think you are all correct -- the problem is that my system is too light (4 6V 420 ah batteries deivering 12 volts) to feed the microwave. The inverter is 2000w pure sine wave. I read a related article that points to the same issue. The learning continues !
    I run my microwave on the same 4 x 6 Volt battery bank... the inverter is a 3000 watt pure sine(Chinese) and it says 1650 watts while in cook. The cables from the batteries are massive and short.
    Perhaps you need some bigger cables.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #17
    Re: Microwave Blues

    picotech.com

    Looked it up , same product, different seller.
    thanks.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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