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  • #16

    Re: ac refrigerator on inverter

    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).

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

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    • #17

      Re: ac refrigerator on inverter

      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.....)

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      • #18

        Re: ac refrigerator on inverter

        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.

        -Bill

        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, 13:46.
        20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

        Comment


        • #19

          Re: ac refrigerator on inverter

          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.
          http://tinyurl.com/LMR-Solar
          http://tinyurl.com/LMR-BigLug
          http://tinyurl.com/LMR-NiFe

          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

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          • #20

            Re: ac refrigerator on inverter

            Re: ac refrigerator on inverter

            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?

            Comment


            • #21

              Re: ac refrigerator on inverter

              Re: ac refrigerator on inverter

              True PFC converters/equipment should also run fine on DC too (check with Mfg. first).

              How are you making the 144 VDC? Multiple solar chargers chargers on series connected batteries? Or something else?

              Did you address any code issues with the >60 VDC of NEC--or it does not matter in your area (being way off-grid--it probably does not matter).

              Sounds interesting in any case.

              -Bill
              20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

              Comment


              • #22

                Re: ac refrigerator on inverter

                Re: ac refrigerator on inverter

                Originally posted by jacobs View Post
                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?
                Oh yes ! There are inverters that have 20+ "steps" in the output, the original Mod Sine Wave. then there are the ones with 2 steps, one more than a square wave. The 2 step mod-sine is really more like a square wave, and that's what's toasting folks stuff.
                http://tinyurl.com/LMR-Solar
                http://tinyurl.com/LMR-BigLug
                http://tinyurl.com/LMR-NiFe

                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

                Comment


                • #23

                  Re: ac refrigerator on inverter

                  Re: ac refrigerator on inverter

                  We have 3 sets of 11 12volt panels wired in series. The reason for the high voltage is in 1980 when we started building our home, our wind generator was about 1500' from the house and we had to go with 120vdc to keep voltage losses within reason. At that time PV's were selling for over $20 a watt. Adjusted for inflation that's about $50/watt today. Later when PV prices came down, we abandoned the wind generator and installed PV's and upgraded to 144vdc. We've since added even more panels.

                  We had electrical inspections while we were building but the NEC wasn't as stringent as it is today. They didn't care what voltage or what type voltage (ac or dc) you were using. You could even install your batteries under your bed if you wanted to! The big issue then was grounding. At that time, the NEC only applied to anything over 50 volts and it didn't address off grid installations.

                  Comment


                  • #24

                    Re: ac refrigerator on inverter

                    Re: ac refrigerator on inverter

                    How are you doing the charge controlling? From what little I know--I have not seen any commercial 144 VDC solar charge controllers out there...

                    Did you make your own? Dump type controller?

                    -Bill
                    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

                    Comment


                    • #25

                      Re: ac refrigerator on inverter

                      Re: ac refrigerator on inverter

                      Interesting reading which may explain the problem I had with my HVAC.

                      Three years ago, I had a furnace ignitor circuit problem. Everything in the Off Grid house ran perfectly from high end electronics, computers, A/C, fans, security system, appliances, well controls, etc except the furnaces wouldn't cycle properly.

                      After bedevilling the electricians and furnace manufactuerer for a couple of months (unfortunately for me during the winter) it turned out a simple $20 capacitor installed on each furnace immediately corrected the problem. They have run and cycled perfectly ever since.

                      Since we had installed four SWs' this was an unexpected problem. I wonder if installing the newer XWs' would have avoided the problem.

                      Always learning something new here.
                      Last edited by Mangas; January 20th, 2009, 5:47.
                      Off Grid 4x5500SW Plus Xantrex SinePlus Inverters/48V DC System/44x185W Sharp Panels/64xTrojan L16-REB 6v/Two Outback FlexMax 80s'/Water Miser Caps/Inverter Managed Air Extractor System/Output to two 100Amp AC Service Panels/Two Communicating 3 Ton Central Air Conditioning Units & Air handlers/Propane Generator CumminsOnan RS20000/RASTRA House Construction

                      Comment


                      • #26

                        Re: ac refrigerator on inverter

                        Re: ac refrigerator on inverter

                        jacobs
                        I was not nearly as fortunate with my Kirkland refers, 18cf energy star made by Whirlpool. The first one I bought at Costco lasted about 6 months of full time use on a cheap msw inverter. I returned it to Costco and they gave me another and at the same time I upgraded to a X brand DR2412. The second refer lasted 10 months of full time use before the motor burned out. Took it back to costco and got my money back. Costco is a great place to do business. I then went to sears and got an 18 cf Kenmore and also bought an Outback VFX 2812, that was 4 years ago and have had absolutly no refer problems. In my case the pure sine wave inverters are well worth the exta money.
                        Larry
                        Off Grid in Bahia de Los Angeles, Baja Norte , Mexico. 2 stacked Outback VFX2812 inverters, 12 Evergreen 190w PV (2.28 kw), 2 Homemade solar trackers, FM 80 and MX 60 charge controllers, E-meter(same as Link 10) battery monitor system, 6-2v Enersys DDM AGM 125-33 batteries@2000amp hours, Kubota 6.5kw diesel gen. Outback X-240 transformer.

                        Comment


                        • #27

                          Re: ac refrigerator on inverter

                          Re: ac refrigerator on inverter

                          Originally posted by BB. View Post
                          How are you doing the charge controlling? From what little I know--I have not seen any commercial 144 VDC solar charge controllers out there...

                          Did you make your own? Dump type controller?

                          -Bill
                          There's a charge regulator factory installed in the inverter. The inverter was made by Michigan Energy Works. Prior to purchasing this 144vdc, 3kw, 10kw surge transformerless inverter in 1999, I constructed my own dump type charge regulator.

                          Comment


                          • #28

                            Re: ac refrigerator on inverter

                            Re: ac refrigerator on inverter

                            High quality MSW and TSW inverters are very similar in efficiency. The idle power of the TSW inverter will be higher than the TSW though. Two to three times! Some one mentioned that the TR was an upgrade and power factor corrected? It is not power factor corrected and was redesigned to be built in China rather than the US. It may be a good inverter though. I have looked inside mine and was for the most part very impressed over my DR design from 1992. I have not turned it on though. Magnum has the only PFC charger in a MSW inverter to my knowledge. PFC charging makes a HUGE difference in efficiency! The DR charger was probably 35% efficient. The Magnum is about 90%.
                            Fridges do run hotter on MSW, but it is not usually a problem. It all comes down to how well the compressor was built. Things seem to be made cheaper and cheaper these days, so it is probably more of an issue now vs. when all there was were MSW inverters twenty some years ago. I was the mechanical engineer for all the Trace inverters, some Xantrex, all the OutBack and some of the Magnum products. As inverters go, everything is better today than back in the days where you bought a Trace or a Trace. Appliances have become fussier though. UL is going to quit approving MSW inverters soon. There are compatibility issues.

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                            • #29

                              Re: ac refrigerator on inverter

                              Re: ac refrigerator on inverter

                              Originally posted by Robin Gudgel View Post
                              ...Some one mentioned that the TR was an upgrade and power factor corrected? It is not power factor corrected and was redesigned to be built in China rather than the US.
                              According to the Xantrex website specs:
                              New power factor corrected (PFC) charging, combined with a more sophisticated multi-stage battery charging algorithm, reduces electricity draw and generator run-time..
                              Are you saying they really are not. Now even I am confused
                              Northern Arizona Wind & Sun Forum & Website Administrator

                              Comment


                              • #30

                                Re: ac refrigerator on inverter

                                Re: ac refrigerator on inverter

                                Originally posted by Robin Gudgel View Post
                                Fridges do run hotter on MSW, but it is not usually a problem. It all comes down to how well the compressor was built. Things seem to be made cheaper and cheaper these days,
                                From what I read a while back.. someplace.. the reason that some new appliances have problems with MSW is because they have been redesigned to meet Energy Star standards, and one way of doing that is to use smaller more compact motors, which means they also have more of a problem in dissipating heat.
                                Northern Arizona Wind & Sun Forum & Website Administrator

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