Off grid cabin build: 115 vs 230 volt submersible pump?

Madmarc

Hi! Thought it best to post specific questions rather than dozens of questions in a sea of sentences.

Question: Which is better, or more specifically which is able to operate more efficiently on an off grid solar only system?

Our situation: well pump at 120' Well head 100' from cabin.

Thanks!
Marc

inetdog

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

Madmarc wrote: »

Hi! Thought it best to post specific questions rather than dozens of questions in a sea of sentences.

Question: Which is better, or more specifically which is able to operate more efficiently on an off grid solar only system?

Our situation: well pump at 120' Well head 100' from cabin.

Thanks!
Marc

Simple answer: It depends....

The differences in efficiency between two different pumps with the same input voltage can be greater than the differences between two otherwise identical pumps at different operating voltages.
But, if otherwise comparable, the 240V pump (nominal 230) will use half the current that a a 120 (nominal 115) volt pump will use. That will allow you to use 1/4 (not just 1/2) as much expensive copper or aluminum wiring for the 220' from your cabin to the pump.

That could be a deal maker for most people. You should also have more variety available in 240 volt models.


Take a look at the Grundfos pump models, some of which will run off almost any AC or DC input voltage and have the advantage of very small or zero staring surge to bog down your inverter or generator. They are pricey, but for some off-grid situations may pay off in the long run.

waynefromnscanada

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

Another thing to consider is what you have for an inverter. If it has 220 volt output available than go with a 220 volt pump. If you only have 115 volt inverter, then you will require a step up transformer with the expense and losses that go with it.
One of the most important things to consider is a 2 wire + ground pump, or a 3 wire + ground pump. The 3 wire models have an external starter box with Capacitor start, far easier (less surge) to get started than the 2 wire units, regardless if 115 or 230 volt units.
Most off the shelf 1/2 hp sub pumps will top out at roughly 100 PSI at the pump outlet. The water will naturally find its way up the pipe to the level of the water in the well, regardless of how far down the pump is. If for example the water level is 100 feet down, it will require roughly 50 PSI just to get the water to ground surface. In that case, the total max the example pump could provide after getting the water to the surface, would be less that another 50 PSI, for a total of 100 PSI at the outlet of the pump. But to be safe, in this example, plan on no more than 30 PSI at the well head - - - if indeed the water level is 100 feet down.
There are other models of these standard, off the shelf sub pumps that pump only 5 GPM instead of the "normal" 10 GPM, and the lower output pump produces higher pressures. It has more, but smaller impellers than the standard model, thus lower flow but higher pressure.
These are centrifugal pumps, so unlike positive displacement pumps, they don't work harder at higher pressures, in fact higher pressures are easier on them because they don't move as much water. Think of your mother's vacuum cleaner, you plug the inlet or the outlet, and the motor speeds up because of reduced loading, less air or no air is being moved.
And of course you could also consider the Grundfoss. Expensive, but depending on your situation, could be worth it.

Cariboocoot

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

"100 feet from cabin" and 120 feet down = 220 feet of wire.
120 foot deep well = submersible pump around 3/4 HP = 240 Volt motor.

A 240 Volt system will have less Voltage drop across such a distance.
If the pump is the only 240 Volt item then an auto transformer can supply it.

animatt

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

If the pump would be the only 240v item i would vote for 110v pump. Instead of tranformer spend a bit more on thicker cable. I would think the cable would be cheaper upfront and in the long run as wire would tend to have a much longer life than a transformer. If you had longer runs transformer could win out.

I have a 1hp well pump 330ft on 10awg wire. 110v. I bought 110v as can be powered from my backup inverters as well as my main. Wire cost about 160 dollars. And easier to find a generator that supply 110v in a pinch. I would have gone with smaller than 1hp but that was what i had on hand.

But having a autotransformer could be useful to future system expansion.

Cariboocoot

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

A 1 HP pump should not be 120 VAC. The current draw on start-up would be enormous; far above what even a 20 Amp circuit could handle. Very bad design. You are getting away with it because of all the resistance in the wire. As a result, your 1 HP pump is probably performing like a 1/2 HP pump. But nobody ever checks these things so since it "works" the engineers are wrong. Right?

animatt

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

I understand what your saying. But for my situation it works. My points are valid and my be worth consideration. Although it wastes copper in transmission of power it saves transformer cost. But you do need a power source that kind supply peak current. I know 8 awg in my case would be more appropriate. My 1hp pump is using. Roughly 750watts based on trimetric. Less than 7amps over 330ft 4.7 % voltage drop.

Cariboocoot

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

animatt wrote: »

I understand what your saying. But for my situation it works. My points are valid and my be worth consideration. Although it wastes copper in transmission of power it saves transformer cost. I know 8 awg in my case would be more appropriate. My 1hp pump is using. Roughly 750watts based on trimetric. Less than 7amps over 330ft 4.7 % voltage drop.

746 Watts is 1 electrical HP. Now there's a coincidence.

But you can't always expect this to be the case, as the pump ratings can be misleading. The harder it has to work, the more current. A 1/3 HP pump should run at ~250 Watts, yet they may draw 800+ if they are working hard. Getting the pump sized right for the water need is the first step. It's not good to have too small or too large of a pump. You lucked out.

animatt

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

I would have bought a .5hp in my case if readily available as i am pumping water just 20ft down. It was either the 1 hp or the 1.5hp. I am in mexico and selection were i was, was a bit limited.
I was suprised myself at how close the pump was to using 746.

Cariboocoot

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

animatt wrote: »

I would have bought a .5hp in my case if readily available as i am pumping water just 20ft down. It was either the 1 hp or the 1.5hp. I am in mexico and selection were i was, was a bit limited.
I was suprised myself at how close the pump was to using 746.

This happens practically all the time.
The 'ideal' pump size works out to be 0.67 HP which doesn't exist, so you put in a 1/2 HP and make it work harder or a 3/4 HP and let it work less. The latter is better for the pump of course.

Your pump is loafing along and should last a very long time indeed!

mike95490

Re: Off grid cabin build: 115 vs 230 volt submersible pump?

There is also the power factor of the motor, and all the system losses. My XW inverter logs my 1/2 hp pump, at about 1,000 watts. It pumps to an elevated holding tank and runs 1x a day for about 3 hours. I am well within the spec'd lift/volume curve for my pump.