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  • Rain Barrel Pump Setup

    Hello, I was looking to design a small DC pump setup for my rain barrel system (4 55-gallon barrels). However, the more I looked into things, the more confused I became, so I thought I'd ask for some guidance!

    This project is half for fun and half because I don't want to have to run power out to this system. We just need a small pump to get the water from our barrels to the flowers around the house a couple times a week (assuming there is enough water). My original thought was the following system:

    2.8gpm 12V pump
    18Ah AGM battery
    20W panel
    Charge Controller

    However, after more research, I'm not sure if I have enough Ah in the battery, or a big enough panel to keep it charged above the 50% level (in Chicago BTW). Does this seem reasonable or am I low on the battery and panel size?

    Thanks!!

  • #2
    That 12V pump will draw 3 amps so basically 36watts. With the 18Ah battery you will be able to run the pump maybe 1 1/2 hours a day which calculates to about 250 gallons (without any losses). That may or may not be enough water for you.

    To be safe I would go with at least a 35 Ah battery and and 80 watt panel otherwise you may end up killing that battery sooner then you want to.

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    • #3
      Originally posted by SunEagle View Post
      That 12V pump will draw 3 amps so basically 36watts. With the 18Ah battery you will be able to run the pump maybe 1 1/2 hours a day which calculates to about 250 gallons (without any losses). That may or may not be enough water for you.

      To be safe I would go with at least a 35 Ah battery and and 80 watt panel otherwise you may end up killing that battery sooner then you want to.
      Thanks! That's just the type of information I was looking for. Looks like upsizing to the 35Ah battery and 80 watt panel would probably only be ~$80 more. Although the cost of a new 18Ah battery is only $35. So I guess there's probably a balance in there.

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      • #4
        Originally posted by longstate View Post

        Thanks! That's just the type of information I was looking for. Looks like upsizing to the 35Ah battery and 80 watt panel would probably only be ~$80 more. Although the cost of a new 18Ah battery is only $35. So I guess there's probably a balance in there.
        A quick rule of thumb for charging any lead acid battery is to have a C/12 to C/18 charge rate. Where C = Ah rating of the battery. So a 35Ah battery needs about 3 amps to 4.4 amps of charging and most 80 watt panels will provide about 4 amps at best.

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        • #5
          Originally posted by SunEagle View Post

          A quick rule of thumb for charging any lead acid battery is to have a C/12 to C/18 charge rate. Where C = Ah rating of the battery. So a 35Ah battery needs about 3 amps to 4.4 amps of charging and most 80 watt panels will provide about 4 amps at best.
          Thanks! Based on your recommendation (and the constraints of my budget), I did size up some to a 20Ah battery and 30 watt panel. Should hopefully end up within that desired charging ratio.

          We will see how it goes. I'll post the results later for people's future reference!

          Comment


          • #6
            Originally posted by longstate View Post

            Thanks! Based on your recommendation (and the constraints of my budget), I did size up some to a 20Ah battery and 30 watt panel. Should hopefully end up within that desired charging ratio.

            We will see how it goes. I'll post the results later for people's future reference!
            You are welcome. Let us know how your system performs and if we can help you in any way.

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