I need to be educated on how to power at real pump for a pressurized water system

Bud1951 · June 2021

I've been trying to figure this one out for a while but I was a millwright/pipe welder/machinist instead of an electrician. I need some help translating stuff into something I can follow.

I have an RPS system that has 400 watts of solar panels feeding a controller which powers a 24vdc in ground pump. The controller also charges two 12v AGM batteries wired in series for 24vdc output. I've been running a SurFlo 24v pump for my garden but now it won't support the sprinkler. I guess it's already worn out. Rather than rebuild it two or three times a year someone here suggested going to a cast iron ac pump which sounds great to me but I need to learn more.

The ground water is pumped into a 1600 gal storage tank and the supply for the SurFlo (soon to be ac) pump comes off the bottom of the tank about 3 feet below the pump so a shallow well pump will easily handle the lift. It already has a pressure tank in the system, too.
It was suggested to go to a 24v inverter to power a 115vac pump that will also provide water to the house about 100 yards away and about 15 feet higher than the pump.

Here's the question - what watt inverter do I need and how many more batteries do I need to add to the battery bank? How do I calculate the watts/starting watts for a pump? I've seen calc sheets but not one that covers this application.

I was thinking along the lines of this for a pump -

https://www.lowes.com/pd/Superior-Pump-Jet-0-5-HP-Cast-Iron-Convertible-Jet-Well-Pump/1002778748

Also, I know the amp hrs/watts have to calculated but would it be better to run the pump on 115vac or 240vac? It looks like the inverter I'll need will start at around $800 but that's much easier to deal with than not having water here in the hurricane zone.

Thanks for any input! Directions to a solar site that deals with this stuff will be appreciated, too!

JRHill · June 2021

Bud, what is a lay of the land? For example we are on a gradually sloping platue. The shop is up above us 15' and I guttered it to fill storage tanks. The garden and livestock tanks are on the other side of the house ranging from 25 to 50' of drop from the tanks. That gives us a reasonable enough pressure for service where needed as long as the water lasts. If you are flatland, well, never mind. You haven't mentioned if you have grid available or not, I suspect not.

Our water well has a Grundfos 11sqf pump (at 165') that takes anything from around 50-250+DCV or about the same in range in AC. No switching, polarity, nothing - it just figures it out on its own and pumps. NO INVERTER. I run it on 4 200watt panels and a small Morningside controller and 8 golf cart batteries for night time if needed. At 48vdc it draws about 780 watts max and is a slow start so no surge. The pump was pricey but has had flawless operation since new. If the batteries run low I can plug it into the house system. There's a click of the transfer relay and now its 120vac. In the summer with no rain we water from the house system hydrants. During the day the pump can run continuously and still put a few watts to float the batteries. A few years ago I added a 2nd 80g pressure tank - we run 55 to 75psi and when needed to refill the storage tank during the day from the house manually.

So my point is to reconsider the pump. Instead of inverter, wire, etc, etc, just go with a direct feed DC pump (and also one that can run on whatever AC might be available). The well has been in service for 12 years and all I've done is replace the batteries 5+ years ago. We know that the water system is critical. If we lose water we might as well open the gates and find a room 50 miles away.

Maybe a system redesign is in order instead of the direction your post was asking?

Critical piece parts other than the well column:
Grundfos pump;
AC/DC Transfer switch (the Grundfos switch I have seems to be obsolete but a std xfer switch would do, wired correctly);
Storage or pressure tank;
Shut off, pressure or float.

Hope this helps.

Bud1951 · June 2021

Thanks for the info! Sounds like a the system I should have gone with! I already have an RPS 24vdc pump set about 85 ft deep. That pump fills the 1600 gallon storage tank. The tank is on the ground and in this part of Fla we have some minor rolling hills. From the house to where the solar well is located is about 100 yards and the tank is maybe 15 feet lower than the house. If I get a chance and can get access to materials I'll drain the tank and build a telephone pole tower to set it on.

We have power at the house and I could run it to the well but we're looking for an off grid water supply that we and the neighbors can depend on after a hurricane has killed the local grid. We quit having live stock when we left NC so this one is purely for convenience - and keeping mama happy!

wellbuilt · June 2021

Why not just pump water with the rps pump you have from the ground to the house in a emergency

wellbuilt · June 2021

Why not just use a second RPS pump from the tank ?

By the time you buy a inverter , pump , battery’s , solar panels to charge the extra batterys and hook it all up .

I think you will be at the same price point as a rsp pump system .

I’m seeing systems for 1500 bucks on anazon

mike95490 · June 2021

Once you calculate your water needs (gallons @ PSI ) you can choose a pump. ( don't forget the PSI ;loss in the 100 run to house)
240v pumps are slightly more efficient then 120V

The following chart has pump motor power requirements. begin with the START. That's the AC starting amps. convert that to watts, and that's what your batteries, cables and inverter have to supply.
looking at line 1 1/3hp. 230v 25.7A Volts x Amps = watts 230 *27.5 = 6,325 watts for 3 seconds. Most good 4kw inverters could have enough surge capacity to start that motor. Don't forget other loads may be running and you won't have full power, since some of it is going elsewhere.

Image: https://us.v-cdn.net/6024911/uploads/editor/rz/zncbwre9dell.jpg

tommy · August 2021

I am looking for a booster pump that will deliver 60 psi to my house and run off solar and batteries at night. Not sure if your chart applies to booster pumps. If so then my start amps are 42.5 for a 1/2 hp on 115 volts.., meaning I need about 5k watts. Does that mean that I need a 5k solar array and a 5k inverter to run one pump? And how many 200AH batteries would I need if I ran it 4 times for 15 minutes at night?

mike95490 · August 2021

the chart applies to induction motors with a starting winding. 1/2 hp, 3 wire, will run at about 1,000 watts. Starting will need about 5kw for a 3 second surge. Your batteries and wires, need to support that load without voltage sag, or the inverter will trip offline. if your water is already at ground level, you only need a small booster pump. If you have a deep well pump & a pressure tank, that is different. Expand more about your system, how high you have to lift the water and such

I need to be educated on how to power at real pump for a pressurized water system

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