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Powering water-air conditioner with a 12 V battery

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  • Powering water-air conditioner with a 12 V battery

    Hi,

    I was trying to power my water-air conditioner with a lead acid deep cycle 12V 76Ah battery. this a.c is very simple ; it only has a water pump and a fan. Total power usage is around 300W. my battery was full when I started testing, and I used a modified sine wave 500W inverter (12V to 220V). It worked fine for 1 hour and then the battery voltage was very low ; 10.6 V according to the controller's reading.

    I am not sure why this happened....based on my calculation, operation for 1 hour of this AC will result in roughly 0.3kWh energy consumption which is (0.3kWh/0.78kWh= 38% of the battery's capacity)....i was expecting at to go at least 60% or 50% before the voltage reduces sharply...

    Can someone explain why this happened? I know that in general, recommended DOD is 40-60% ...but lets say we exceed that, will the battery's voltage drop so much so that the inverter will shut off (note in my case here, the inverter DIDN'T shut off ..i turned it off myself)......

    Further, can someone give me a general estimation for how to power this AC for 6 hours at night? I mean the recommended battery capacity.

  • #2
    Ok a 76 AH battery is only good for less than half of the AH rating, and if your using a car/truck CCA battery even less. You are using an inverter to run what could be easily converted to a DC fan and pump, eliminating the need for an inefficient inverter. If your battery was not new for this project, has already been damaged? or wrong battery for the job. Did you initialize charge your new or re-purposed battery. Have you taken Specific Gravity readings? do you have the tools? Do you know how? do you know what to do based on your SG readings? Do you have distilled water on hand. Have you used a meter to take readings, so you know exactly how much power the unit uses? If that unit really uses 300 Watt hours, your battery only has about 450, so about 1.5 hours run will kill your battery.

    Comment


    • #3
      I can help you out here. The very short story your battery is grossly undersized.

      The fist thing going on is batteries have what is called Peuket Affect or Peukert'S Law that states: change in capacity of rechargeable lead
      MSEE, PE

      Comment


      • #4
        What the heck happened to my post MODS. It was a very detailed explanation I am not going to bother with rewriting.

        Short answer OP you ned a 12 volt 750 AH battery.
        MSEE, PE

        Comment


        • #5
          Originally posted by Sunking View Post
          What the heck happened to my post MODS. It was a very detailed explanation I am not going to bother with rewriting.

          Short answer OP you ned a 12 volt 750 AH battery.
          And perhaps an example that brevity is the soul of both wit and clear communication.

          ( I know - said the person prone to epistles, like the pot calling the kettle black/practice what I preach, etc.)

          Comment


          • #6
            Originally posted by J.P.M. View Post

            And perhaps an example that brevity is the soul of both wit and clear communication.

            ( I know - said the person prone to epistles, like the pot calling the kettle black/practice what I preach, etc.)
            I gave a very detailed answer, but the Forum Software decided to delete it and lost it. It cost me 10 minutes of time I am not going to spend again.

            MSEE, PE

            Comment


            • #7
              Originally posted by Sunking View Post

              I gave a very detailed answer, but the Forum Software decided to delete it and lost it. It cost me 10 minutes of time I am not going to spend again.
              Been there, done that - or had it done to me I guess. Sucks. Happy Sat.

              Comment


              • #8
                And I so wanted to hear what you had to say. Too bad, lol

                Comment


                • #9
                  Sorry. I don't know what happened to Sunkings post, maybe Solar Pete has an answer. There have been other reports of this happening too, but mod's cant do anything, it's an Admin issue.

                  Regarding the battery going dead. You have several things working against you.
                  Mod sine inverter - cheap, but they cause motors (your AC has 2 of them) to consume about 10% more power than nameplate rating.
                  Small Battery - The faster you consume power from a battery, the less power it can provide. see https://en.wikipedia.org/wiki/Peukert's_law

                  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


                  • #10
                    Originally posted by Sunking View Post

                    I gave a very detailed answer, but the Forum Software decided to delete it and lost it. It cost me 10 minutes of time I am not going to spend again.
                    Hello SK, did you have multiple links in the post, or did you mention the k word ( k i t c h e n )

                    Comment


                    • #11
                      Originally posted by solar pete View Post

                      Hello SK, did you have multiple links in the post, or did you mention the k word ( k i t c h e n )
                      No Sir, no links whatsoever.

                      I can give you a clue what might be going on because the common thing I have noticed is when I copy and past Text from another website like I did this time with Peukert Law definition to save some time. Use to do it all the time with no problems.

                      I know better to post a link on first reply because it takes Mod Approval before it gets posted. That started happening when you upgrade VB about a year ago. I know to Save, and then comeback in a put the links in and it goes OK without Mod Approval.

                      Here is the offending TEXT and SOURCE. I removed the links and replaced with plain Forum Text.

                      EDIT NOTE

                      Now I can get it through for whatever reason

                      change in capacity of rechargeable lead-acid batteries at different rates of discharge. As the rate increases, the battery's available capacity decreases.

                      Something is not right. Hope that helps you track the bug down.Kill it if you find it.
                      Last edited by Sunking; 01-07-2017, 07:39 PM.
                      MSEE, PE

                      Comment


                      • #12
                        Howdy SK I think it is to do with particular formats of text, we had issues where people were attempting to embed code and the system is now very sensitive to certain formats and doesn't seem to like anything that is copied and pasted from other websites, well that is how it was explained to me (for memory). If you want to copy and paste from another website I think you first need to put it into word or a text file.

                        I have been messing around with settings lately, notice we have had basically had no spam for the last couple of weeks , but this seems to be having a few side effects, I cant really go into detail about what I have been doing as that would just give a heads up to the damned spammer army. I have a couple of other things that I need some time with the programmers to get done, hopefully that should happen in the next week or two, cheers.

                        Comment


                        • #13
                          For whatever reason, I have noticed in the last week or so that the Forum is having a really bad time with formatted text.
                          In particular if you copy in text that has any outside HTML format tags or formatting codes (almost anything in square brackets) long or short it will sometimes preview the entire text correctly but when you try to post it it cuts off around the first formatting tag.

                          I am starting to copy the finished text into my computer copy buffer before saving.
                          If it does not work, I copy in again, hit the Source button to show all formatting and try to clean it up into something that will paste.
                          It may also be affecting some quotes. It is a royal pain.

                          My sympathy, SK.

                          If it would only show the truncation on Preview it would be less likely to screw people over.
                          SunnyBoy 3000 US, 18 BP Solar 175B panels.

                          Comment


                          • #14
                            I generally use windows notepad as a Text Strainer, it takes out all formatting and leaves plain ASCII
                            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


                            • #15
                              Originally posted by Logan5 View Post
                              Ok a 76 AH battery is only good for less than half of the AH rating, and if your using a car/truck CCA battery even less. You are using an inverter to run what could be easily converted to a DC fan and pump, eliminating the need for an inefficient inverter. If your battery was not new for this project, has already been damaged? or wrong battery for the job. Did you initialize charge your new or re-purposed battery. Have you taken Specific Gravity readings? do you have the tools? Do you know how? do you know what to do based on your SG readings? Do you have distilled water on hand. Have you used a meter to take readings, so you know exactly how much power the unit uses? If that unit really uses 300 Watt hours, your battery only has about 450, so about 1.5 hours run will kill your battery.
                              Well its a new a battery (lead acid not a car battery)..only a few months old...my initial estimate was : for a 10 hours runtime on battery, i will need (300Wx10= 3kWh-- which means : 3000/780= 3.8--so i will need 4 batteries like this one which gives a total Ah of : 4x65= 260 Ah)...and assuming 50% DOD, i will need 2 times this size so: 260x2= 520 Ah--basically 8 batteries)...is this calculation correct?

                              But i didn't understand some of the questions u posted here: about specific gravity (whats that got to do with this system?)..distilled water on hand??...i don't have any kWh meters currently,..so no i didn't take any readings except voltage readings using a standard 10A controller.....i didn't get how u calculated that my battery has 450 Wh//(isn't it : 12 x 65= 780Wh)...then we multiply it by 50% or 60% depending on DOD?

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