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Correct Design? Solar-direct and Battery Hybrid (temporary)

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  • Correct Design? Solar-direct and Battery Hybrid (temporary)

    I'm running a manufacturer-designed solar-direct pump (Dankoff 24v 6amp Solar SlowPump) for running sprinklers at a remote location. Until my grass seed germinates, I've decided that I'd like to temporarily soak the ground during the night and I'd like to learn how to set up the battery side of my system. (This is all a big experiment to teach myself backwoods solar applications anyway.) I'm running one 24v 8amp panel through the proprietary charge controller for that pump (and other Dankoff pumps)

    I'm wondering if someone here can tell me how to link in the battery charging side of the equation (stuff in blue on the diagram). Everything in black is solar-direct and currently working.

    Two questions:

    1. What will happen if I don't include a timer that will prevent the battery from charging at the same time as the pump is running? There is extra amperage coming from the panel (a couple amps). I'm guessing it'd trip the breaker, but I don't know if the charge controller is smart enough to know that there's an 6 amp draw on the leg -- and if the charge controller will adjust to take whatever amperage is left after the pump draws. I can't imagine that would work unless the charge controller is smart. My solution is to run a timer that will prevent the battery being charged during the use of the pump. How's that sound? My charge controller is an HQST 30amp PWM Smart Solar Controller or I can order whatever might work.

    2. What will happen if the direct leg of the system is supplying 6 amps to the pump and the battery is in the loop? I'm guessing the amperage will pour back toward the battery and jack it up without a diode, since there's no charge controller on that leg. Do I need a second timer on that leg just to prevent back-flow of power into the battery?

    This is getting complicated and I'd move to a pure battery-based system instead of solar-direct, but I'm only planning on using the battery-based night irrigation for a couple weeks -- and I don't want to buy a new pump. After the seed germinates, I'd like to go back to solar-direct.

    Any help is greatly appreciated. Solar Irrigation Wiring Scheme.jpg

  • #2
    Without speculating on what the "proprietary" charge controller is doing, I'd suggest just taking it out of the picture entirely. Connect the panel to the HQST charge controller, the charge controller to the battery (with a fuse or breaker in between!), and the battery to the pump timer (with a fuse or breaker in between!). The DC- side of the pump should connect back to the DC- of the battery.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      Originally posted by JOracle View Post
      I'm running a manufacturer-designed solar-direct pump (Dankoff 24v 6amp Solar SlowPump) for running sprinklers at a remote location. Until my grass seed germinates, I've decided that I'd like to temporarily soak the ground during the night and I'd like to learn how to set up the battery side of my system. (This is all a big experiment to teach myself backwoods solar applications anyway.) I'm running one 24v 8amp panel through the proprietary charge controller for that pump (and other Dankoff pumps)

      Two questions:

      1. What will happen if I don't include a timer that will prevent the battery from charging at the same time as the pump is running? There is extra amperage coming from the panel (a couple amps). I'm guessing it'd trip the breaker, but I don't know if the charge controller is smart enough to know that there's an 6 amp draw on the leg -- and if the charge controller will adjust to take whatever amperage is left after the pump draws. I can't imagine that would work unless the charge controller is smart. My solution is to run a timer that will prevent the battery being charged during the use of the pump. How's that sound? My charge controller is an HQST 30amp PWM Smart Solar Controller or I can order whatever might work.
      No real big problem. Your pump just runs until it completely drains the battery dead. Any off grid solar system charges the battery and runs the equipment at the same time.

      There is really no point in answering any more of your questions because this is just not going to work or ever happen. You simply do not have the equipment to make it work, and when you find out what it will take, will decide it is not worth spending the money or time.

      Your pump if powered from a battery will pull 150 watts. You did not say how long you want to run it at night so I will guess 10 hours. That means you would be using 1500 watt hours. To do that even on a temporary basis is going to require a a 24 volt 180 AH, a 250 pound $700 battery.

      To support that battery with your 30-Amp PWM charger to replace the 1500 watt hours used every day is going to require you to buy 2 more panels.

      If you only want to run it on batteries, then you are going to have to buy and come up with a timer and switch to do it automatically.

      So as you can see, this is just not going to happen. You are not going to go spend another $1200 to make grass grow. Being somewhat of a gardener, last thing you want to do is water at night. You are asking for mold and mildew diseases. All your seed bed needs is to be moist, not drenched. You want water early so by night the top layer of soil is dried out so the seed does not rot.

      FWIW your drawing is completely wrong.
      MSEE, PE

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      • #4
        In order to get the seed to germinate (which is the goal), I think I'll only need two hours of water pressure per night. Does that change anything?

        In the alternative, I can run the night watering as long as I can afford before reaching 50% discharge on my small battery bank (I need to look at my LA batteries and see what AH they're rated for.)

        Thanks for the info! I'm learning! I appreciate the patience. (This stuff is like alchemy.)
        Last edited by JOracle; 07-10-2017, 10:47 AM.

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        • #5
          The solution from ancient times is to fill up a tank when the sun shines (used to be when the wind blows).
          Turn on your sprinkler later. Tanks are cheaper than batteries, more efficient too. Bruce Roe

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          • #6
            It means you would need a 24 volt 80 AH, 110 pound $300 battery, switch and timer. Use the pump to fill a tank during the day without a battery, then water at night for the seed to rot in.
            MSEE, PE

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            • #7
              Sorry Bruce you beat me to it.
              MSEE, PE

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              • #8
                Thanks, guys. Done. 55Ah batteries and running the whole thing off a standard MTTP charge controller. It's working great. Much appreciated.

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