regulating PV output for driving motor

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  • Tim Green
    Junior Member
    • Oct 2011
    • 4
    #1

    regulating PV output for driving motor

    Hi,

    kind of new to electrical stuff so need a little help. I am trying to run a pond oxygenator directly off a solar panel but the motor in the oxygenator runs wild when the panel is in full sun. I know the panel i have is much bigger than the one that is usually supplied with the oxygenator but I want the thing to keep pumping even in more overcast conditions. The device is 3.5v-6V, 0.8W and the panel is 6V, 5Wp. Is it excessive voltage or power that is causing the motor to race and how to best rectify?
    Thanks
    Tim

    edit: sorry, posted in wrong place i think!
    Tags: None
    • Sunking
      Solar Fanatic
      • Feb 2010
      • 23301
      #2
      Same answer. Solar PV panels are current supplies, not voltage. You need a charge controller and batteries to regulate power.
      MSEE, PE

        Comment

        • RCinFLA
          Member
          • Aug 2011
          • 41
          #3
          You can sometimes run a DC motor directly off a panel. You should check what the unloaded, open circuit voltage is on the panel to make sure it doesn't go too high for the motor. With a motor that draws only 0.133 amps and a panel capable of up to 0.8 amps you will operating at near the unloaded panel voltage much of the time.

          PV panels are illumination based current source. One potential problem is low illumination may result in insufficient current to turn the motor. Question is what happens to heating on motor at this low current when it is not turning. With such a small motor you will likely be okay.

            Comment

            • Tim Green
              Junior Member
              • Oct 2011
              • 4
              #4
              thankyou

              Thanks to both of you for the info/advice. I think I'm grasping things a little better now.
              I did a little test to try and control the excess voltage from the 6V panel by putting a battery into the circuit but with a diode to stop the battery from being able to drive the air pump. Works very well and the pump runs well in bright-overcast to full sun conditions without over-cranking.

              Have decided now to integrate the oxygenator circuit with my solar garage lighting set-up. Basically the same circuit as I mentioned above but using a 20W 12V panel and a 12v-6v converter to the air-pump. Excess voltage is again "soaked up" by a battery (this time via a charge controller) and the battery runs the garage lighting.

              It's odd how you set out to make a very simple system and then find that the slightly more complicated one is actually easier. This time I had all the components in an existing setup so didn't need to buy anything extra...always a bonus!

                Comment

                • Mike90250
                  Moderator
                  • May 2009
                  • 16020
                  #5
                  The other thing that can be done, is to use a Linear Current Booster, which is designed to power a motor directly from PV, and overcome the problems of motor stalling
                  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

                    • 4321loco
                      Member
                      • Sep 2009
                      • 80
                      #6
                      I've got a small 6v solar panel 9v open circuit,It's like 5x5 inchs or maybe bigger, not sure on wattage but if your in USA I can give it to you......might be like 2-3 watts, I was gonna chunk it yesterday

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