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Thread: ac refrigerator on inverter

  1. #11

    Default Re: ac refrigerator on inverter

    A 3kw inverter seems pretty big to run a refrigerator.

    During the hurricanes here in Florida back in 2004 I ran an energy star refrigerator off of my APC SmartUPS 750XL. It ran fine, I think it is a true-sine-wave power supply. But my mom's refrigerator, non-energy star, would trip the UPS so it wouldn't run. I had to run back and forth between my in-law's house that had electricity to charge it up occasionally.

  2. #12
    Join Date
    Sep 2007

    Default Re: ac refrigerator on inverter

    Thanks crewzer

    Too many changes here, forgot to go and find it.
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  3. #13

    Default Re: ac refrigerator on inverter

    Also keep in mind there are vast differences in "MSW" inverters. In fact, a lot of what are called MSW inverters really are not modified sine wave. They are really modified square wave or just plain square wave inverters. MSW inverters can have a wide range of wave forms and unless the information is available or you put it on a scope you have no idea what your really getting. Needless to say if you have a $99.00 3000 watt inverter, well you probably have a $99.00 wave form. The Xantrex DR/TR inverters (and I would guess the Magnum) are some of the best MSW inverters and are in no way comparable to a cheap "MSW" inverter. In fact, the Xantrex SW inverters were really a MSW inverter that have a wave form so good that they could classify it as a true sine wave. But many people that have switched from SW inverters to Outback, Magnum, or the XW inverters have noticed a noted improvement in the operation of some equipment like refrigerators and microwaves. I would plug almost anything into a DR/TR inverter but I would not plug anything worth more than 99 cents into a cheap "MSW" inverter. So just keep in mind "buyer beware" when it comes to "MSW" inverters.
    2.6kw stc, XW4024,2-XWMPPT, SCP, 1760ah 24v flooded gc2.

  4. #14
    Join Date
    May 2006
    Florida, USA

    Default Re: ac refrigerator on inverter

    There are only two compressor manufacturers, Samsung is one, other is also Korean but don't remember name.

    New refrig compressor achieve energy star improvement with variable speed compressor. They should be run on true sinewave inverters.

  5. #15

    Default Re: ac refrigerator on inverter

    We've used modified sine wave inverters exclusively for over 26 years for refrigeration, 240 volt submersible well pump, laundry, large and small shop tools, electronics & etc. We live in an area that no one has commercial power and most of our neighbors have MSW inverters and have had NO problems powering various loads including refrigerators. MSW inverters are more efficient, less expensive, and less complex that TSW inverters. I personally see no reason to switch to a pure sine wave inverter. Simplicity is beautiful!

  6. #16
    Join Date
    Mar 2006
    SF Bay Area (California)

    Default Re: ac refrigerator on inverter

    I am very glad that your MSW inverters are working well for you... Since they are so much less expensive--if somebody can use them, it often does not make sense to use a TSW.

    However, MSW inverters are not more efficient when you look at the entire battery to load connection... Especially if that load is inductive (transformers and electric motors).

    Simply, because of the shape of the wave form (square wave), there are a whole lot of higher frequencies (above 50/60Hz) in the square wave that motors and transformers cannot use. These extra frequencies only are converted into heat... Approximately 10-20% of energy usage.

    Only with true resistive loads (heaters filament lamps) do MSW and TSW inverters approach equal efficiencies (modern TSW inverters are getting really good at being efficient).

    With more complex electronics (CFL's, Microwaves, electronic devices), you pretty much are left to getting a kill-a-watt meter and running the loads on TSW and MSW sources and seeing how they perform.

    For motors that run a short time (say a well pump running 10 minutes a day), the losses with a MSW inverter are not that great. However, for something that runs many hours per day (fridge, lighting, home electronics, fan, etc.) the losses may be more substantial (as well as the possibility of equipment damage from long term accumulation of heat build up).

    I believe I read somewhere (here?) that, for example, a Microwave oven on a MSW inverter takes longer to heat. However, there is a Panasonic "Inverter" Microwave Oven that does very well on MSW (looking on Amazon, the Inverter Ovens have a very mixed bag of love/hate reviews, and may not be available at this time).


  7. #17

    Default Re: ac refrigerator on inverter

    A very high percentage of electronics built today including CFL's employ a bridge rectifier at the input to change ac to dc. It doesn't matter if it's fed pure square wave, modified sine wave, pure sine wave, OR 144 volts dc. Transformers and their inefficiencies are mostly a thing of the past. Microwaves are only used a few minutes a day. You are correct an ac electric motor is more efficient when fed pure sine wave but when you consider the total load used in an average off grid home, the ac motor equation is insignificant. I stand by my original statement.....modified sine wave inverters are more efficient due to their simpler design. KISS (keep it simple.....)

  8. #18
    Join Date
    Mar 2006
    SF Bay Area (California)

    Default Re: ac refrigerator on inverter

    Actually, a bridge rectifier/voltage doubler front end on most electronic devices of any size has pretty much gone away (by US and International requirements) because of the very poor power factor (only take current very near the peak of the AC voltage waveform, giving a very narrow, very high amperage current spike 120x per second). The poor power factor is from a bridge front end causes large losses in the building wiring and transformers--both because of the spectrum content (high frequencies) and because of the I^2*R heating losses cause by the amplitude of the current spike.

    You can read a bit about the issue here:

    A particularly important class of non-linear loads is the millions of personal computers that typically incorporate switched-mode power supplies (SMPS) with rated output power ranging from a few watt to more than 1 kW. Historically, these very-low-cost power supplies incorporated a simple full-wave rectifier that conducted only when the mains instantaneous voltage exceeded the voltage on the input capacitors. This leads to very high ratios of peak-to-average input current, which also lead to a low distortion power factor and potentially serious phase and neutral loading concerns.

    A typical switched-mode power supply first makes a DC bus, using a bridge rectifier or similar circuit. The output voltage is then derived from this DC bus. The problem with this is that the rectifier is a non-linear device, so the input current is highly non-linear. That means that the input current has energy at harmonics of the frequency of the voltage.

    This presents a particular problem for the power companies, because they cannot compensate for the harmonic current by adding simple capacitors or inductors, as they could for the reactive power drawn by a linear load. Many jurisdictions are beginning to legally require power factor correction for all power supplies above a certain power level.

    Regulatory agencies such as the EU have set harmonic limits as a method of improving power factor. Declining component cost has hastened implementation of two different methods. To comply with current EU standard EN61000-3-2, all switched-mode power supplies with output power more than 75 W must include passive PFC, at least. 80 PLUS power supply certification requires a power factor of 0.9 or more.[3]
    Also, with AC bridge rectifiers running on MSW inverters--they can run into serious under voltage issues.... The typical MSW peak voltage is very near that of the AC RMS voltage of 120 volts... The peak voltage of a pure sine wave is sqrt(2)*120 volts AC RMS = 170 volts (voltage doubler front ends, typically used with 120/240 VAC switchable power supplies, would be 240 vdc on MSW vs 340 vdc on TSW).

    With many electronics (and motors) being "constant power" devices, anything that lowers the useful voltage or pumps in unusable current will increase overall power consumption (power needed plus power losses due to MSW AC power).

    With the new PFC supplies, they should run pretty well on MSW inverters as they "emulate" the transfer characteristics of a resistive load (the "ideal" load).

    Modern TSW designs, while not cheap, can approach 95% efficiency just on the conversion from DC to AC for even very large systems (like the Xantrex XW family--up to 6kW click on technical specs. for PDF download).

    I am not arguing that MSW does not work for you--but there are many reasons that many folks would end up being much happier with a TSW inverter to run their loads.


    PS: Here is a nice PDF Download / Power Factor Correction paper... It is written convince people/mfg'ers to upgrade their products to PFC and 80%+ efficient designs--so the paper still has an editorial slant... But it does a through job of addressing the isssue.

    You can look at the efficiency graph of the 300 watt TSW MorningStar inverter... ~6 watt idling load; roughly 0.6 watts if in standby (waiting for an 8 watt minimum load).
    Last edited by BB.; January 19th, 2009 at 13:46 PST.

  9. #19
    Join Date
    Sep 2006
    Willits, CA

    Default Re: ac refrigerator on inverter

    If you happen to have a fridge that does not like MSW (most are actually a square wave, with a step in them), you have to replace the fried motor fairly often. What model/brand fridge do you have that works well with the MSW inverter ? That would help a lot of folks in their shopping.

    Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
    Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe battery | 15, Evergreen 205w "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT

  10. #20

    Default Re: ac refrigerator on inverter

    Quote Originally Posted by mike90045 View Post
    What model/brand fridge do you have that works well with the MSW inverter ? That would help a lot of folks in their shopping.
    Refrigerator: Kirkland Model ST18HPXKQ02 energy star made by Whirlpool (Previously used very successfully on msw) Currently using a 15 year old 12vdc RF19 SunFrost powered by an Iota converter on 144vdc. Iota, Todd, and Progressive Dynamics converters will all run on 120vac or 144vdc. They all have bridge rectifiers on their front ends.

    Freezer: 9 year old 15 cubic foot GE Model FCM15SAB on modified sine wave.

    Some of our lighting is CFL's on 144vdc. Most CFL's DO work on 144vdc.

    With the success we've had, we sure don't need pure sine wave. Maybe there's a difference in waveform between different brands of msw inverters?

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