The endless DC/AC pump question

[confused]

Is there a good reason why a submerged DC deep well pump will not work, if you run an AC power supply to the well head to an AC/DC transformer and power the pump from that.

I have a feeling that this is a really stupid question but I don't see why.

The reason for my query is that my well is 300 meters from and out of sight of the house. Putting in a sophisticated Solar pumping system is an advert to thieves looking to steal anything not nailed down. I have a 3Kw inverter that can power an AC pump if need be but DC is so much more efficient and I'm happy to pump slowly over a longer period of time.

Due to thieving no-goods, I currently pump using compressed air but this is even less efficient than an AC pump. It does have the advantage of only leaving 2 plastic pipes in the well.

Regards
Confused

[inetdog]

Is there a good reason why a submerged DC deep well pump will not work, if you run an AC power supply to the well head to an AC/DC transformer and power the pump from that.

I have a feeling that this is a really stupid question but I don't see why.

The reason for my query is that my well is 300 meters from and out of sight of the house. Putting in a sophisticated Solar pumping system is an advert to thieves looking to steal anything not nailed down. I have a 3Kw inverter that can power an AC pump if need be but DC is so much more efficient and I'm happy to pump slowly over a longer period of time.

Due to thieving no-goods, I currently pump using compressed air but this is even less efficient than an AC pump. It does have the advantage of only leaving 2 plastic pipes in the well.

Regards
Confused

There is no reason that supplying power to a DC pump using AC to a DC power supply (not called a transformer!) at the well head would not work. It may not be the most efficient way to do it though.
Some DC pumps have controller units which will accept either AC or DC input over a wide range of voltages. (In effect they include the DC power supply.) You may be able to send DC at a high enough voltage that the wiring losses over the 300 meters are reasonable, so you should explore that option. Use aluminum wire for the 300 meter run as it will both be less expensive for the same current capacity even though the aluminum wires will be larger, and it will be less attractive to wire thieves.
High voltage DC on the wires will also be more of a hazard to a thief than AC, which could either be an advantage or a disadvantage depending on your outlook.

[Sunking]

but DC is so much more efficient and I'm happy to pump slowly over a longer period of time.

Not exactly sure where you came up with that idea but it is very flawed for your application. DC motors efficiency range from 50% up to around 80%. The cheapest AC motor is 80% and induction AC motors up around 97%. Not to mention AC motors will last a lot longer and less expensive.

[peakbagger]

If I had to guess I believe that the efficiency he discussed is regarding the pump. Pumps that are usually driven by DC motors are usually posiitive displacement which are usually 95 % plus mechanically efficient. Pumps typically driven by AC are usually multistage centrifugals and may be 70% mechanically efficient per stage. Of course the inefficiency of the DC motor will offset at least part of the efficency gain associated with a positive displacement pump so the overall pump and motor efficiency is specific to the configuration.

[billvon]

Of course the inefficiency of the DC motor will offset at least part of the efficency gain associated with a positive displacement pump so the overall pump and motor efficiency is specific to the configuration.

Good DC brushless motors are actually more efficient than an equivalent AC induction motor. In DC motors, the field is created by permanent magnets. In AC motors the field is created by induced current in the rotor; this is power that cannot be used for creating torque and is essentially wasted.

However, AC is typically chosen over DC because they are incredibly rugged, lighter, and do not require a controller; they can generally accept AC power directly. A three phase induction AC motor is among the simplest motor systems possible.

[confused]

Thank you for your replies gentlemen.
I was referring to the nature of the pump as regards efficiency.
Your replies at least keep my options open.
It is a vexing issue. How to pump a minimum of 1000 liters a day without having the hassle of humping up through the olive groves to find that some ne're do well has cut through the fence, smashed through the brick well head, pulled the contents of the well out and run off with it. Only to return after a few weeks to see if you have replaced your pump with a bright shiny new one.
I lost a Lorentz PS200 mini and it's controller, which saddens me to this day. The only saving grace was that the panels were to heavy for them to make off with at the same time.
I periodically search for new alternatives to my airlift pumping, without the need for expensive controllers and solar panels to installed in what is clearly an exposed location.
Should anyone have any ideas, I'd love to hear them.
In that regard, I have an 8 inch well, 90 meters deep. Water level at 17 meters and I pump from 40 meters down, so 23 meters below water level. The water flows from the well head down hill to a 6000 liter tank, some 40 meters above the house. The well is 300 meters from the house.
I currently pump using a 2hp compressor and a 6Kw diesel generator or weather permitting a 3000W inverter. I also have a PTO compressor that runs off of my old tractor.

regards
Confused

p.s. currently welding a new secure well cap, inspired by Ned Kelly's helmet.
p.p.s I particularly liked the reference to the dangers of a DC cable as far as thieves are concerned. Fizzle, fizzle, pop!
That is precisely what happened to a chap not far from here a month ago, whilst stealing live high tension cable. What was he thinking? Sadly we'll never know.

[NeilTheCop]

Perhaps a windmill.
Rusty barbed wire around the tower is a great discouragement for thieves

[confused]

Good afternoon NeiltheCop, you read my mind.

Sadly, even that option looks a little pricey. I keep up an periodic search for air compressors that could run off of a smallish windmill and still achieve a minimum of 5 bar. Gast seem to produce compressors that would do the job, but they cost a fair bit and that is before even contemplating making or purchasing a windmill.
Unfortunately, I am unable to site a turbine at the well head, as it would conflict with an site of historical importance, thus the 300m run on either cable or air-hose.
Airlifttech.com make the perfect windmill/compressor system which if I had 5000 bucks, I'd purchase in a heartbeat.
Still, I haven't given up and my lonely vigil continues.
Any thoughts or links to dirt cheap air engines/compressors would be appreciated.
Regards
Confused

[Txtinner]

Lama to the rescue!

I bought a Lama once to keep wild dogs away from my goats, and they also kept anyone away that didn't know how to work with him.
If you didn't bring him a head of lettuce, and let him eat before any other animal, you couldn't take your eyes off him, or he would jump on your back and spit at you. Nasty green spit too.
I buy, sell, and trade Boer Goats at the local Livestock Auction, and see some Lamas come through, or you will find them on Craigslist.
If you are close to the Dallas / Fort Worth area, I'll help you out.
Have had issues at my Hobby Farm in the past with people too lazy to get a job.