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I'm lost. Need to power a DC irrigation pump.

DaveCaddell

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Jul 12, 2020
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I need to power a pump to bring water in from a lake for maybe an hour or two daily (max) with a pump that uses 230v and runs at 11.2a (to water lawn, etc).

I know it's sad that I can watch all these great tutorials and still be lost, but I am. Can anyone help an old man figure out how to get this done? What size panels and battery I need?

Once I learn how to do these things, I want to go solar on everything!

Thank you in advance!

Dave
 
The issue that may drive the inverter size is the startup Amps for the pump. Is there any way you can find out that information? Other members with experience may be able to estimate the start up current from the 11.2 Amps you reported above.
 
I agree with @Ampster, it's the surge that's going to be difficult to manager, unless the pump has some kind of 'soft start' mechanism?

But in general, 230V x 11.2A = 2,576W (VA for the purists, I'm assuming unity PF for the sake of simplicity), my guess it that your pump will surge three times that. But let's assume surge is sorted, a 3,000W inverter preferably running off a 24V (nominal) battery pack would do you. Running 2,576W for two hours is 5,152Wh, that's around 214AH at 24V of Lithium ion or around 429AH at 24V of lead-acid. Lithium ion is about $500 per 100AH, so $1,070. Lead-acid is about $100 per 100AH so $429.

In order to replenish 2,576Wh per day, you'd need ballpark 644W PV in Summer, 2,576W PV in Winter, though I guess you won't be doing much water pumping in Winter!

Edit: Ooops, double the prices, forgot it's 24V.
 
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Most pumps publish a "locked rotor" current or "surge current" multiple. I'm guessing that's about a 3hp pump. Most submersible pumps have a surge on the scale of 5X run, and it's not for a trivial amount of time.

A soft start mechanism is almost always required, and all solar pumping kits include something like this. A line of Grundfos 3" submersible pumps have these built in.

These guys sell complete kits: https://www.rpssolarpumps.com
 
Thank you all for the comments.

The pump is a Goulds GT20. It's a 2HP irrigation pump and is NOT a submersible pump. I'm still noodling around with the idea.

Best,
Dave
 
When designing the system for powering my well pump, I purchased a Fluke clamp meter with "inrush current" capability. Inrush is the startup current that the motor draws just in the first 1/2 second or so that it starts. I my case, my 1hp Grunfos pump draws ~9.5amps running, and 37-38amps at startup. Note though that a regular clamp meter might briefly show a somewhat higher current draw at startup, but your typical meter does not respond fast enough to measure the real startup current. So 38A/9.5A = 4. If your pump runs on 11.2 amps, I'd suggest your startup is likely to be 44-45amps (11.2A X 4=44.8A).

Here's a second meter that's far cheaper than the Fluke that seems to work just as well.
I'd recommend getting this one.

Now, getting back to your situation, my personal recommendation is to have enough solar power to run the pump live, without drawing from the batteries. On rotating mounts, I can expect my arrays to put out about 75% of their rated capacity more or less between 9am and 3pm. So, dividing 2575W/0.75 = 3430W of panels. If you build rotating mounts like this, you might squeeze six grid-tie panels per array, for 1500-1800W per array. Two of these arrays turned to point at the sun, and the system will work.

Now, for the inverter. You are talking about 10,400W of startup power, and I can name two different brands of inverters that can handle this kind of surge. Mine is the Schneider XW+6848. The second is Outback's Radian GS8048A. Both can handle startup surges as high as 12,000.

Of course though, some of these numbers are estimates. It's your job to get a clamp meter to actually measure your starting current, then you'll be on firm ground to actually design your system to handle your real-world numbers. Get back to us again when you have these, and then we can proceed further in your overall design.
 

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I found an installation manual for that pump dated Nov. 2015, so there may be a later design. It does not list the locked rotor or surge amps, but it does say to fuse it at 40 amps. And for a circuit breaker, a non delay breaker should be 40 amps, a delay type breaker should be 25 amps. The full load running amps is shown at 13.9 amps. You should definitely have at least a 40 amp surge current rating to get that thing started.

The manual also lists wire gauge requirements. It is only calling for #12 wire at 150 feet. That seems a bit light for a 40 amp surge. That is nearly 0.5 ohms of wire resistance. At 40 amps, that would drop 20 volts or so. That is almost a 10% sag.
 
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