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  • Water Pump DC or AC?

    I am setting up a small 400w system on a remote cabin. It will be running through a 40a PWM charge controller, to a battery bank of two 12v 200ah batteries then to a Xantrex 1800w inverter. I will only be powering lights on this system with exception of a small water pump for a toilet and a sink (Shurflo 3 or 3.5gpm). My lights will be running AC off the inverter. My question is in reference to the water pump itself. Is there an advantage or disadvantage of running a DC water pump directly off the batteries/charge controller or running an AC pump off the inverter? I can purchase the pump in 115v ac or 12v dc. The run from the battery bank to the pump would be less than 20-22 feet.

    Thank You,

    VICK
    Last edited by cvick; 09-25-2018, 04:09 PM.

  • #2
    If you used a much smaller sine wave inverter, you can save a lot of power. If you need over 1,000 w of power, you need to have a 24V system
    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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    • #3
      OK thanks. Maybe I should have just asked - is it more efficient to run a water pump from DC output of inverter or the AC output of inverter.

      Thanks,

      VICK

      Comment


      • #4
        Originally posted by cvick View Post
        OK thanks. Maybe I should have just asked - is it more efficient to run a water pump from DC output of inverter or the AC output of inverter.

        Thanks,

        VICK
        NO

        you are asking questions and throwing terms around like you think you know something.

        You need to design a system. A design is not done by grabbing parts off the shelf at an RV dealer or hardware store.

        Slow down, take a breath and write out what you need.

        I'm not sure what the specs of the Shurflo pump are, compared to what you need. First start with pressure. Do you need 10 psi of water, or 30psi ? Toilets will slowly refill at 0.5gpm, faster with more flow. What sort of pressure do you need at the sink, shower ?

        Where is the water source ? An IBC tote on the ground outside ? A spring level with the cabin ? A well 8 feet down? a well 80 feet down. Those all use different pumps. Some can run from DC , some not.

        DC pumps often have brushes that need replacement every couple years.

        Your AC power . The larger the inverter, the more self consumption is has. a 1800w inverter will burn more power internally, and a couple LED lights in your cabin can consume, in a small system, that makes the difference of dead batteries in the morning, or if you have power after 2 cloudy days.

        I'm trying to help you have power, and not dead batteries. I doubt my nightime lighting load in a 2 person 200sf house exceeds 80watts at any time. Thats a lot of LED lighting.
        Look at the self consumption specs of several inverters and find one that consumes less power than all your loads consume.
        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


        • #5
          My system has plenty of power for my needs. I've already written all this out and I already own the system and am just adding the water pump to it. The water is coming from a water tank above ground level that actually exerts water pressure without the pump. I can run a gas powered pressure washer right off the tank it has outflow pressure. The pump is needed to add extra pressure for shower etc. I am just in need of knowing (mainly for knowledge) if a DC pump or an AC pump is a more efficient pump if they are comparable in size and style, just out of curiosity more than anything.

          Thanks

          VICK

          Comment


          • #6
            When I bought my place in Baja the kitchen water pump was under the sink. Funny thing the 12 volt source was in the garage, approx. 100 feet away. The 12 volt power was ran in conduit with 10 awg. wiring. It worked. I thought I'd measure the voltage at the pump just for the fun of it before I changed the location of the 12 volt battery bank. I was getting just over 9 volts. The pump had been running off this source for many years. You should be fine with DC power to your pump. You wont have the losses from inverting the power that way.
            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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            • #7
              Thank you, this is what I was trying to determine. If it was more reasonable to take the loss of converting to AC or to just run it direct with DC. I am not so much concerned with exact efficiency on this system but for future knowledge it was something I was curious about. Thank you.

              Comment


              • #8
                Originally posted by cvick View Post
                I am setting up a small 400w system on a remote cabin. It will be running through a 40a PWM charge controller, to a battery bank of two 12v 200ah batteries then to a Xantrex 1800w inverter.
                OK Vick that is a poorly designed system and throwing away a lot of money. Your first and biggest mistake is using inexpensive PWM Controller makes everything else real expensive. Using two parallel 12 volt 200 AH batteries is stuck inside a 12 volt toy box and a perfect plan to destroy the batteries as fast as you can. That is your plan, a very poor plan. Something a DIY would do.

                First thing that does is you just turned 400 watts of panels into 260 watts with only 22 amps of charge current, which is only 1/2 the current required for a 12 volt 400 AH battery you plan on doing. You need at least 700 watts using a PWM Controller to support those batteries.

                Since you stated 400 watts of panels on a PWM controller, I can only assume you are using 4 x 100 watt 12-volt Battery Panels, and that is a huge mistake which is going to cost you a lot of money to make them work. It requires you to wire all 4 panels in parallel which is the last thing you would want to do. 4 parallel panels requires 4 times the wire, much larger wire, a Combiner with Fuse Blocks to combine them vs wiring in series. With just 1 or 2 parallel strings none of that expense is required. But with PWM operating at toy voltages of 12 volts, you threw all that away along with a lot of cash.

                Smart money would have been to use much less expensive Grid Tie Panels of 200 watts each wired in series. Half the mounting harware, and 1/4th much smaller less expensive wire with no fuse or combiners needed or required. Only catch is you have to use a MPPT Controller. Yes MPPT controllers are more expensive than PWM, but in a system saves you hundreds of dollars of equipment cost and a lot less labor and materials. Here is where you will really kick yourself when you see the LIGHT. A 400 watt MPPT system generates roughly 33 amps of current vs 22 amps using the same panel 400 watts of panels with a PWM System. Put another way it takes a 600 watt PWM system forcing you to use very expensive (1/2 $/watt or 50% less expense) 12 volt battery panels instead of using much less expensive Grid Tied Panels. If Battery panels cost $2/watt a 600 watt then panel cost is $1200, or smart money buys 400 watts ($1/watt) of Grid Tied Panels for $400 and gladly pay up another $400 ($800 total for panels and controller) for a good 40 Amp MPPT Controller and let a sucker buy PWM controllers and battery panels.

                I am not even going to touch on how bad an idea of using parallel 12 volt batteries and a very dangerously over sized Inverter. But here is an idea of how poorly you matched things up.

                An 1800 watt 12 volt inverter requires a minimum 12 volt 1400 AH battery. All you have planned is 400 AH. You are not even close to having enough battery to support much Inverter. At 1800 watts screams for a 24 volt or even better a 48 volt battery system. Once you go over 500 watts of Panels or Inverter , you step out of the 12 volt toy box you are stuck in and move up to 24 volts up to 1500 watts. Above 1500 watts falls in 48 volt territory. .

                A 12 volt 1400 AH requires 140 amps of charge current. If using PWM would require 2 x 80 Amp PWM Charge Controllers and 2500 watt of panels split between the two controllers and a copper mine to make all the wire the size of your wrist to make it work. A very expensive 12 volt toy box you are stuck inside of. Bet you have never heard 2 4, and 6 volt batteries or 24 or 48 volt solar systems. That is what happens when you are stuck inside a 12 volt toy box.If you only knew how dangerous a 12 volt 1800 Inverter is I bet you would scrap your whole idea and fix it.




                Last edited by Sunking; 09-26-2018, 02:08 PM.
                MSEE, PE

                Comment


                • #9
                  Yes, I am a DIYer. Yes, I am not skilled in this field. I have been, however, working with someone at Grape Solar that has told me to do as I have. I purchased the system equivalent to this:

                  https://www.homedepot.com/p/Grape-So...-203505963-_-N

                  I was told that two 12v 200ah hour batteries would be sufficient for running a small cabin with this set up. The problem that I am having is that I am being told completely different information from every person I speak with on the systems. Yes, I am aware that the PWM controller is less desired and efficient charge controller. I am aware the system I have is a cheap, off the shelf "hardware store" system that is nowhere near as efficient as it could be. This is however a simple kit I can purchase off the shelf and install myself to power a few lights and a pump 8-10 times a year, probably once a month or less. I am not looking to power an extensive system. I am not needing a Ferrari here. I just need some thing to get me from point A to point B safely. I do want it safe and if this is not safe, as you have outlined, I have a real problem on my hands as I have been directed by others to build this system and it be a safe system. If you are stating that it is not safe I will be immediately going back to them.

                  Thanks,

                  Vick

                  Comment


                  • #10
                    Vick personally I could care less about you or what you do. I am a licensed professional engineer (PE) with about 40 years of direct experience. That means I am liable for my work.

                    So ask whoever sold this to you; What size wire and fuse does it take between the Batteries and Inverter?

                    Its a trap question you already know the answer too. If they answer incorrectly you know they don't know WTF is going on. If they say anything less than a 1/0 AWG with a 200-amp fuse, they have no clue what they are talking about. Anything less is dangerous and does not meet minimum electrical codes.

                    If they answer correctly and say use 1/0 AWG and 200 amps fuse your next question you should ask is how would you terminate that 1/0 cable to the Inverter? Another Trap question because the Inverter Input Terminal is too small and cannot terminate a 1/0 AWG conductor.

                    FWIW a 1/0 AWG is about the size a cigar, .35 inch diameter. Try to find a place to stick it in. House wiring cannot handle 200 amps except your service wire from the utility, and yould never draw 200 amps, but at least the wire and fuse is capable of it if demanded.

                    Having said all that I am confident you can make what you have work except the Inverter.. Wire your panels configured 2S2P 2 in series, 2 in parallel and configure the two batteries in series for 24 volts, Use a 24 volt 1000 watt or less Inverter. Then use an AC powered water pump. It will cost you a lot less to install be safe, and will work. Not ideal, but better than what you have now. Makes the most of what you have and meets your needs. That is what I do for a living.
                    Last edited by Sunking; 09-26-2018, 05:41 PM.
                    MSEE, PE

                    Comment


                    • #11
                      Because your electricity is weak, this is a problem for your water pump , which is being used.

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