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  • High Voltage Battery Only with 240v Inverter? What's the highest efficiency possible?

    I need to power an air conditioner that runs at 240 volts AC and I have a battery from an EV that is around 400 volts DC. My solar panels are hooked directly to the battery as a 390 volt string which keeps them topped up in the sun, so all I want is the inverter to run directly from the battery without complicating things or losing efficiency.

    The Solaredge inverters claim 99% CEC efficiency and have the correct voltage ranges, but those seem to require the Solaredge optimizers to function. Same goes for the Huawei brand, also 99% CEC and needs optimizers (I assume the work the optimizers are doing allow the Inverter to "cheat" out that last percent that other inverters don't get?)

    Is there a "dumb" standalone string inverter that will just take 400 volts DC and output 240 volts AC without requiring any other hardware, or needing a constant load like the grid would have?

  • #2
    Hello NotGonnaLie and welcome to Solar Panel Talk

    I have not heard of a stand alone inverter like that so my guess it would be a very unique piece of equipment. The only ones that will accept a high DC input voltage and produce 240V AC are grid type or hybrid inverters. Although those are usually connected to solar panels and not a battery for the DC input

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    • #3
      You may be able to find a used industrial UPS that uses a high voltage battery, and salvage the inverter from it.
      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister

      Comment


      • #4
        Originally posted by SunEagle View Post
        Hello NotGonnaLie and welcome to Solar Panel Talk

        I have not heard of a stand alone inverter like that so my guess it would be a very unique piece of equipment. The only ones that will accept a high DC input voltage and produce 240V AC are grid type or hybrid inverters. Although those are usually connected to solar panels and not a battery for the DC input
        Thank you. Do you suppose something like the SMA SunnyBoy would treat a battery hookup as if it were PV? I don't see anything about the SunnyBoy requiring extra gear to be connected to the solar panels, unlike the SolarEdge stuff.

        Originally posted by Mike90250 View Post
        You may be able to find a used industrial UPS that uses a high voltage battery, and salvage the inverter from it.
        True but I doubt they are prioritizing efficiency at all, I'm not going to see anything like the 95-99% range these PV string inverters have. Trying to power off-grid air conditioning from a solar-charged battery array, I want it to be as efficient as possible, even if I have to pay a premium.
        Last edited by NotGonnaLie; 09-24-2021, 03:22 PM.

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        • #5
          Originally posted by NotGonnaLie View Post

          Thank you. Do you suppose something like the SMA SunnyBoy would treat a battery hookup as if it were PV? I don't see anything about the SunnyBoy requiring extra gear to be connected to the solar panels, unlike the SolarEdge stuff.



          True but I doubt they are prioritizing efficiency at all, I'm not going to see anything like the 95-99% range these PV string inverters have. Trying to power off-grid air conditioning from a solar-charged battery array, I want it to be as efficient as possible, even if I have to pay a premium.
          Well solar panels are current sources while a battery or power supply are voltage sources. I don't think a DC battery will work but then again I have been proven wrong in the past.

          Comment


          • #6
            I will point out, that it might be possible to run an air conditioner DIRECTLY from
            your 400VDC battery, skip the inverter. I am talking about the latest mini split
            units, which can be more than TWICE as efficient as old stuff. Here the input is
            250VAC, but that is immediately rectified to around 350VDC to drive the variable
            speed motors. Skip the rectifier (and the inverter), go in direct with a big power
            savings (and other advantages).

            This is how the Conditioning units powered directly from solar panels work, often
            with a line backup input. Have not tried it yet, more research needed. Bruce Roe

            Comment


            • #7
              Originally posted by bcroe View Post
              I will point out, that it might be possible to run an air conditioner DIRECTLY from
              your 400VDC battery, skip the inverter. I am talking about the latest mini split
              units, which can be more than TWICE as efficient as old stuff. Here the input is
              250VAC, but that is immediately rectified to around 350VDC to drive the variable
              speed motors. Skip the rectifier (and the inverter), go in direct with a big power
              savings (and other advantages).

              This is how the Conditioning units powered directly from solar panels work, often
              with a line backup input. Have not tried it yet, more research needed. Bruce Roe
              That's fascinating, my batteries are LiFePO4 so they hold an extremely flat voltage curve as they discharge and are almost permanently near at that voltage. How did you discover that those units are doing that rectification to 350 volts DC rectification? I was looking at the Mitsubishi MSZ-FH06NA https://www.mitsubi****echinfo.ca/si...9_201910_0.pdf

              Is there a way that I could confirm that a specific model could be hardwired to the battery, short of purchasing it and opening the unit up? I'm sure the manufacturer isn't keen to expose that info for fear of electrocuting customers.

              Comment


              • #8
                Originally posted by NotGonnaLie View Post
                ........

                Is there a way that I could confirm that a specific model could be hardwired to the battery, short of purchasing it and opening the unit up? I'm sure the manufacturer isn't keen to expose that info for fear of electrocuting customers.
                In addition to heat pump AC units that can be run off DC there are also ones that are variable speed that I assume use an internal inverter to modulate the speed. I have not done a deep dive but I assume most of those are variable frequency three phase inverters. The ones I am thinking about are the ones that have high SEER ratings.
                My next purchase is probably one of those units that can be run off 240 AC so I can use my existing grid tie system to power it. That way when not using the heat pump AC, I can sell excess solar power to the grid with out any additional hardware. Since efficiency is in the title of this thread, that is going to be the most efficient system for me.

                For someone off grid the math is different.
                Last edited by Ampster; 09-24-2021, 07:53 PM.
                9 kW solar. Driving EVs since 2012

                Comment


                • #9
                  Originally posted by NotGonnaLie View Post
                  That's fascinating, my batteries are LiFePO4 so they hold an extremely flat voltage curve as they discharge and are almost permanently near at that voltage. How did you discover that those units are doing that rectification to 350 volts DC rectification?

                  Is there a way that I could confirm that a specific model could be hardwired to the battery, short of purchasing it and opening the unit up? I'm sure the manufacturer isn't keen to expose that info for fear of electrocuting customers.
                  To be sure, find a panel operated AC unit, note the range of panel voltage possible. I
                  have not explored that, or opened up any of the 6 variable speed motor heat pumps
                  here YET. But inside each is an AC motor driven by a DC to AC inverter, no doubt 3
                  phase. My rather high 250VAC line gives 350VDC with a basic rectifier, as the peak
                  is 1.414 times the rms.

                  There are NO USER SERVICEABLE PARTS signs on such equipment, so moving
                  to straight DC input involves good technology and safety knowledge today. Maybe soon
                  it will be possible under warrantee. My first approach will be to see if DC can just be
                  applied to the AC input to flow thru the rectifier, such as the ancient AC/DC radios did.
                  Bruce Roe

                  Comment


                  • #10
                    Looks like this Plug Out Power makes what you want. They supply inverters that convert various Hybrid cars to home generators. I think they are 240VAC output units.

                    Comment


                    • #11
                      Plug out Power looks to be an improvement over the inverter I hooked up to the 12 volt battery in my Tesla. I did not see a price but to deliver 240 volts AC it has to cost
                      more than the $200 I spent.
                      Last edited by Ampster; 09-25-2021, 12:35 PM.
                      9 kW solar. Driving EVs since 2012

                      Comment


                      • #12
                        Definitely a lot more. I think ithat are in the $3,000 range.

                        Comment


                        • #13
                          Originally posted by bcroe View Post

                          To be sure, find a panel operated AC unit, note the range of panel voltage possible. I
                          have not explored that, or opened up any of the 6 variable speed motor heat pumps
                          here YET. But inside each is an AC motor driven by a DC to AC inverter, no doubt 3
                          phase. My rather high 250VAC line gives 350VDC with a basic rectifier, as the peak
                          is 1.414 times the rms.

                          There are NO USER SERVICEABLE PARTS signs on such equipment, so moving
                          to straight DC input involves good technology and safety knowledge today. Maybe soon
                          it will be possible under warrantee. My first approach will be to see if DC can just be
                          applied to the AC input to flow thru the rectifier, such as the ancient AC/DC radios did.
                          Bruce Roe
                          I think see what you're talking about now. Because of how RMS works, changing AC to DC with a bridge rectifier will always get 1.414x the AC voltage input as DC output?

                          Doesn't the rectification introduce some inefficiency? 250 volts AC times 1.414 is 353.5 volts DC. If you were measuring 350 volts DC from a 250 volt AC input like you said, that would suggest the bridge rectifier in your unit is 99% efficient?

                          It sounds like without knowing the efficiency of the rectifier in whichever unit I try to run on straight battery DC, I can't know what the compressor inverter will be expecting / receiving. Unless I actually buy it first and test with a multimeter?

                          Comment


                          • #14
                            As I said this may be an experiment for those with the experience giving good technology
                            and safety knowledge. If a unit has any circuit running directly off the AC input (no I have
                            not taken mine apart YET), it will fail. 99% efficient is about what I would expect from a
                            bridge rectifier at this voltage.

                            The safe way to do this is use HVAC designed to be run directly from solar panels. I do not
                            know if these go up to 390VDC at this time, though my solar system certainly does. Bruce Roe

                            Comment


                            • #15
                              Originally posted by NotGonnaLie View Post

                              .........
                              It sounds like without knowing the efficiency of the rectifier in whichever unit I try to run on straight battery DC, I can't know what the compressor inverter will be expecting / receiving. Unless I actually buy it first and test with a multimeter?
                              Please folks, this is not science lab. This is high voltage gear and if you are guessing or hoping, you are in trouble already.

                              No User Serviceable Parts Inside

                              If you touch the wrong thing, or accidentally short the wrong thing, AC or DC, it's quite possible to kill you....

                              Bruce knows his stuff, I don't know you and you are asking far too basic questions for me to ignore.

                              danger do not touch hurt while you die.jpg

                              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                              solar: http://tinyurl.com/LMR-Solar
                              gen: http://tinyurl.com/LMR-Lister

                              Comment

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