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Producing 24v 60w of DC power from 12v panels

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  • Producing 24v 60w of DC power from 12v panels

    So, I tried to figure this out myself but I got too confused. I'm hoping someone here can help.

    I need to power a DC exhaust fan in my greenhouse. The fan I want to buy can take up to 24v 60w of DC power. It can use less power but not more. I looked around and didn't find many panels that provide 24v 60w of power or something close. Those I did find were pretty expensive. 12v panels are cheaper and I understand there is a way to hook two of them together to provide the power I need. So, my question is what size 12v panels do I need to produce something close to 24v 60w of DC power?

    Thanks in advance for your help.

  • #2
    Hello Henderman and welcome to Solar Panel Talk

    I guess my question to you is how many hours do you need that exhaust fan to run?

    Without a battery you may only get a few hours a day depending on where you live and how much useful sunlight you get.

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    • #3
      I only need the fan during the sunlight hours as I'm venting excess heat from my greenhouse. So it works great without a battery. I live in northern New Mexico and I get a lot of useful sunlight. I have another greenhouse with a similar setup, but a crappy lower powered fan, and I'm happy with when it turns on and off. If this new fan works, I'll probably buy another for my old greenhouse.

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      • #4
        Using enough 12V panels wired in parallel might give you 18V in good sun. If half favored
        east facing and the others west, you might get a couple hours more operation at the cost of
        more total panel watts. Bruce Roe

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        • #5
          How big are the greenhouses ?

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          • #6
            12 x 30'. But I'm not looking for advice on what size fan to use. I'm wondering if I use two 12v panels, what size 12v panels do I need to produce something close to 24v 60w of DC power?

            Comment


            • #7
              Originally posted by Henderman View Post
              .......... I'm wondering if I use two 12v panels, what size 12v panels do I need to produce something close to 24v 60w of DC power?
              To reliably harvest 24v @ 60w, you'll need at least 120w, preferably 150w. you could use 12V panels in series, or 24V panels in parallel.

              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

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              • #8
                So, do I need some kind of controller to ensure I don't exceed 60w going to my fan?

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                • #9
                  You said you could use less power, which is why I suggested enough 12V panels would
                  not exceed 20V, might drop to 15V. If you go to 24V panels, you will need some kind of
                  regulator/limiter to avoid seeing maybe 36V. And it will take a lot more watts of 24V
                  panels since they put out half the current, with the extra voltage being wasted. Bruce Roe

                  Comment


                  • #10
                    Originally posted by Henderman View Post
                    12 x 30'. But I'm not looking for advice on what size fan to use. I'm wondering if I use two 12v panels, what size 12v panels do I need to produce something close to 24v 60w of DC power?
                    NOMB, or concern, but it's usual to have a goal in mind such as how hot/cold you want the air in the greenhouses and under what conditions and use that to determine the air flow and hence fan power required, and then from that figure out how much fan power you need and if you need to change things to achieve the goal(s). Part of that calc. requires area size/volume to be heated/cooled.

                    Forget I brought it up.

                    Comment


                    • #11
                      Originally posted by bcroe View Post
                      You said you could use less power, which is why I suggested enough 12V panels would
                      not exceed 20V, might drop to 15V. If you go to 24V panels, you will need some kind of
                      regulator/limiter to avoid seeing maybe 36V. And it will take a lot more watts of 24V
                      panels since they put out half the current, with the extra voltage being wasted. Bruce Roe
                      OK. Should I be looking for 2 12v 75w panels?

                      Comment


                      • #12
                        Originally posted by Henderman View Post

                        OK. Should I be looking for 2 12v 75w panels?
                        That may work if they are wired in series. Yet if you are concerned about burning out the motor then power it from a 24V battery source and use the panels to charge the batteries. A little more expensive but your fan won't be overvoltaged.

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                        • #13
                          Originally posted by Henderman View Post

                          OK. Should I be looking for 2 12v 75w panels?
                          I proposed keeping them in parallel to limit voltage. Once you series them and generate more voltage,
                          you must protect the motor from it. A full battery plant will certainly do it and allow full 24V operation,
                          but you will multiply complexity and possibly flatten the battery every night, soon destroying it.

                          Some motors will tolerate a lot more voltage than their nominal rating. The "48VDC" fans I used in
                          phone equipment were rated to 56V operation. Check it out. Bruce Roe

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                          • #14
                            The manufacturer says "[FONT=sans-serif][SIZE=15px]Fan motor accepts varying voltages such as those shown on the chart. [/SIZE][/FONT][FONT=sans-serif][SIZE=15px]DO NOT EXCEED 24 VOLTS DC. Higher voltage/amperage [/SIZE][/FONT][FONT=sans-serif][SIZE=15px]on fan motor will decrease brush life.[/SIZE][/FONT]"

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