Modified sinewave inverters and aircon

lazza
lazza Solar Expert Posts: 336 ✭✭✭
in Off Grid Solar & Battery Systems #1
HI

Just a quick question... how would the following appliances react to a 1500W Modified Sinewave Inverter?

a) A simple 1200W resistance heater?
b) An airconditioning unit?

Cheers
Larry
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Modified sinewave inverters and aircon

    A resistance based heater should be just fine...

    With the A/C (or any compressor/refrigeration system), it is sort of unknown until it is tested.

    My theory, if an electronic device/power supply has poor power factor (say 0.70 or less), it may overheat on MSW. If it has good power factor (0.95 or better), I would be less worried. In either case, I would still monitor the temperature of the devices to make sure they don't run hot. (we did have person here who ran a >0.95 PF power supply that died on MSW).

    With motors, they can be designed with a lot of margin (thick wires, lots of cooling, etc.), and even though (in theory) a motor on MSW uses around 20% more power (which goes up as waste heat in a motor)--But does not cause much trouble for the motor (light loads, good cooling etc.).

    With compressors/refrigeration systems, they typically design the motor to run at 100% of rated/design load. So, any extra waste heat can cause problems... Say a motor is 80% efficient. If it is running at near rated load, that 20% waste heat now becomes 40% waste heat--substantially raising the motor's operating temperature (for ever 10C increase in temperature, there is ~1/2 decrease in life).

    I guess, you could put a current meter and/or Kill-a-Watt type meter on the refrigeration system and see how much (if any) extra power/current the unit draws (difference between line power and MSW power). If there is substantually more current drawn, then it is a question how well the unit tolerates MSW.

    The other confusion is some of the nicer A/C units are using VFD's for the motor control. So, now you are back to evaluating AC Power Supplies/PF and trying to figure out how they will behave (the motor will be fine, the input to the VFD, I am not sure).

    Probably the old 80/20 rule... 80% of the electrical equipment will work fine, and 20% may have some sort of issues (running hot, timers not working correctly, noisy, etc.).

    A couple of good inverter FAQs:

    Choosing an Inverter - Home Power Magazine
    All About Inverters

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #3
    Re: Modified sinewave inverters and aircon

    Based on where I come from it would be 90/10 % , 90% have run on MSW for the last 20 years without issues. The only thing I have personally saw have problem is the newest non analog Refrigerators and a clock or two. There just are not that many TSW inverter out there, they haven't been mainstream that long. They still buy MWS because they are $200 cheaper.
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  • firerescue712
    firerescue712 Solar Expert Posts: 95 ✭✭
    #4
    Re: Modified sinewave inverters and aircon

    Last summer, I ran a GE 5000 btu window unit on a Samlex PSE-24175 without any problems. If the AC was shut off with the compressor running, it would sometimes cause a fault on the inverter when trying to restart too soon. After waiting a few minutes, it would start with no problems.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #5
    Re: Modified sinewave inverters and aircon

    I guess if they weren't still popular, our sponsor wouldn't carry so many of them. like I said, I offer them TSW, most will say they are happy with they got. There is a huge difference in the way MSW is implemented.

    http://www.solar-electric.com/maenmosiwain.html


    Is this true TWS ??

    SW4024

    Waveform Sine wave, 34 - 52 steps per cycle
    .
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: Modified sinewave inverters and aircon

    the differences between them are that there's more total harmonic distortion from a msw type than a tsw type. a modsine wave is basically termed a square wave and that is a 100% saturation of a sine wave with harmonic distortion putting it to 29.3% thd. each step added to a square wave going through in a cycle does smooth the average and lower the thd. a true sine wave waveform is rare even from the utilities, but they are kept to 5% thd or less by law so that is what governs the definition of tsw and msw inverters is that distortion. understand that motors, fans, compressors, etc like to run on tsw for the distortion winds up being dissipated as heat in the windings of these items and wastes potential power in a form that does not benefit you. the excess heat and whacky frequencies involved can play havoc with many items even if they seem to be ok as it can shorten the lifespan of the stuff being powered.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #7
    Re: Modified sinewave inverters and aircon
    niel wrote: »
    the differences between them are that there's more total harmonic distortion from a msw type than a tsw type. a modsine wave is basically termed a square wave and that is a 100% saturation of a sine wave with harmonic distortion putting it to 29.3% thd. each step added to a square wave going through in a cycle does smooth the average and lower the thd. a true sine wave waveform is rare even from the utilities, but they are kept to 5% thd or less by law so that is what governs the definition of tsw and msw inverters is that distortion. understand that motors, fans, compressors, etc like to run on tsw for the distortion winds up being dissipated as heat in the windings of these items and wastes potential power in a form that does not benefit you. the excess heat and whacky frequencies involved can play havoc with many items even if they seem to be ok as it can shorten the lifespan of the stuff being powered.
    Do you know what the threshold is when a Inverter would pass over to the TSW designation based on the number of steps in the waveform ?? Is it just a % of distortion ?? The reason I ask is that I have two different clocks, one will run faster on the same TSW inverter.

    There is a world of difference in the TSW, can't believe I listened to those buzzing ceiling fans for so many years.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: Modified sinewave inverters and aircon

    The "standard", at least in the US, is less than 5% total harmonic distortion.

    Regarding the clocks--Perhaps the run reading accurately uses an internal time reference (quartz oscillator), and the one less accurate uses the 50/60Hz from the AC line.

    For whatever reason, many AC inverters seem to not hold very accurate line frequency. Varying by +/- 0.5 Hz is not going to affect many appliances, except clocks (+/- 0.5 Hz is +/- 12 minutes per day on a 60 Hz line).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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