Discharge rates

JudeJude Registered Users Posts: 2
I am putting together a system to permanently power essential systems (well pump, refrigerator, freezer) My problem is that my well pump is a 2 wire with high startup loads, I need around 5kw surge capacity and pure sine wave (explicit manufacturer warning). I have a 2500/5000 12v inverter and 4 12v 125 ah deep cycle batteries. I have measured the amperage when the well pump is running at 12.5 A. Thats about 30A out of the batteries for roughly 30 seconds around 24 times per day. The other draws are relatively low in comparison. I could set it up as a 24v system, but pure sine wave inverters in that range are wll over $1000 (I'm assuming that the $400 chineese models on Amazon are junk?). Will this setup work? Or will it ruin my batteries and justify the purchase of the 24v inverter? I could also buy more batteries, but if I have to spend the money I think I would rather spend it on the inverter.
Thanks

Comments

  • SolarMusherSolarMusher Solar Expert Posts: 172 ✭✭✭
    Re: Discharge rates

    Jude, if your pump draw 12.5Aac (1500Wh) at 120Vac it should draw around 125Adc minimum and not 30Adc on a 12Vdc system. 12mn per day should be around 25/30Adc out of your 500Ah 12V system, it could work for your pump with a good quality pure sine wave inverter but I can't see how you could power pump, freezer and fridge with a small 3kwh at 50% discharge. Better buy stronger batteries to build a one string battery bank that could fit the capacity and autonomy that you need and a 24V inverter/charger that could connect to the grid to charge these batteries.
    I'm in doubt that you will use this pump only for 12mn per day, better plan for 1 hour.
    Someone will correct me if I'm wrong.
    Just my opinion,
    Erik
  • JudeJude Registered Users Posts: 2
    Re: Discharge rates

    Thanks, I will check my numbers. I have good measurements for all of them, just not handy. My concern is that the discharge rate, which I calculated at around 120Adc for the 500 Ah system (30A per battery) is too high and will result in short battery life.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Discharge rates

    Yes, avoid those junk china inverters. You should expect to pay at least $1000 for a good 3000watt PURE sine wave inverter, and that is just for a stand alone inverter. The inverter chargers (and ones that can stack) are closer to $2k+

    And your "basic" loads may appear basic/small to you but in Solar terms, that is not a small system.

    If you have a somewhat new energy efficient fridge that will likely use around 1 to 1.5kwh per day. Freezer, might be be close to 1kwh per day. If they are more than 5 or 6 years old, they could be using double or tripple that. Conservation is cheaper than solar. Better to spend $600 on a new fridge than have to spend twice that on solar just to run the old one.

    And also, consider going up to 24v at least. A 12v inverter will need VERY large (perhaps even double) cables to handle the draw of 2500+w. At 24v you will be at half that current. 48v will be at 1/4 the current and even better.

    Also there are a lot of very efficient 110v well pumps that people on here have recently switched to and have had great luck and very minimal starting surge, etc.
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  • SolarMusherSolarMusher Solar Expert Posts: 172 ✭✭✭
    Re: Discharge rates
    jcheil wrote: »

    Also there are a lot of very efficient 110v well pumps that people on here have recently switched to and have had great luck and very minimal starting surge, etc.
    Agree, see grundfoss pump, very soft start. 1/2 force is 700Wh.
  • mike95490mike95490 Solar Expert Posts: 8,377 ✭✭✭✭✭
    Re: Discharge rates
    Jude wrote: »
    I am putting together a system to permanently power essential systems (well pump, refrigerator, freezer) My problem is that my well pump is a 2 wire with high startup loads, I need around 5kw surge capacity and pure sine wave (explicit manufacturer warning). I have a 2500/5000 12v inverter and 4 12v 125 ah deep cycle batteries.....
    Thanks

    48V system needed with the loads you are running. That will reduce the amps strain on your batteries 4x. Wire the batteries in series, new inverter, re-program the charger. But, your inverter needs to be able to handle the starting surge .
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  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: Discharge rates
    Jude wrote: »
    I am putting together a system to permanently power essential systems (well pump, refrigerator, freezer) My problem is that my well pump is a 2 wire with high startup loads, I need around 5kw surge capacity and pure sine wave (explicit manufacturer warning). I have a 2500/5000 12v inverter and 4 12v 125 ah deep cycle batteries. I have measured the amperage when the well pump is running at 12.5 A.
    Are you sure your 12 V inverter can start the well pump? 12.5 A at 120 VAC is 1,500 w for continuous operation and motors often require 5 to 10 times their continuous rating to start.

    Your battery array seems small for starting the well pump. If they are cold in the winter, then they will have less ability to source the high current. Even when fully charged, their voltages might not stay above 12 V DC when starting the well pump.

    Starting the well pump might require 5,000 W / 12 V / .75 (efficiency of inverter) = over 556 A flowing into the inverter. I think you need at least a 24 V battery array.
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