DC motor

Tex_Ray
Tex_Ray Registered Users Posts: 2 ✭
edited September 30 in Solar Water Pumping #1
Howdy fellows, it’s nice to be here and hope y’all are doing well. My name is RAY and I hope to rely on you folks for a little help. 
From what I’ve read, a strictly DC motor is more efficient than an AC motor with a VFD or inverter that converts AC power to DC power. I see all these so called solar pumps like RSP sells that I believe are nothing more than AC motors that are converted to run on DC power with freq. drives. 
I would like to know if any of y’all know of a submersible pump manufacturer that makes a pump strictly with a DC motor. 

I’d like to have at least a 5-HP. or larger  pump capable of lifting 425’ with about another 1,000’ of 2” pipe of level transfer. 
I’m currently running an 8-HP. Goulds, 480V-3 phase. I’m not looking for anything high tech, I’d just like to manually start and stop the pump and hours of run time are not that important. If I could get six hours a day would be more better than good. Right now my first obstacle is a pump with a DC motor. 
I forgot to mention that I’m currently pumping about 50 gallons a minute. 
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  • Tex_Ray
    Tex_Ray Registered Users Posts: 2 ✭
    edited September 30 #2
    I forgot to mention that I’m currently pumping about 50 gallons a minute. 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,710 admin
    #3
    A quick web page on the efficiency of various types of electric motors:

    https://www.pelonistechnologies.com/blog/comparing-the-efficiency-of-different-electric-motor-types

    In general, Brushed DC motors are about the most inefficient type of electric motor.

    It has been many years (decades?) since I have looked at the efficiency of AC induction motors vs Brushless AC Motors (an electronically commutated permanent magnet motor). I thought that a PM AC motor was more efficient (permanent magnets in the rotor vs using induced magnet field in the Induction motor rotor)... But this web site shows the induction motor is/can be more efficient than a PM motor (I am sure there are lots of design and material and cost issues involved).

    Note a typical PM motor is very similar to a 3 phase motor--Just with a PM based rotor.

    Also a down side is a Brushed "universal" motor does have a limited brush life... From 1,500 to 10,000+ hours (more expensive brushes and better motor design, brushes can last long)--However, This is still not a "long life/low mantenance motor"... There are 8,760 hours in 1 year, so a typical pump may last 1 to a few years in a "cycling" operation... If you have a surface pump motor that I easy to access/change brushes, less of an issue vs a submersible pump.

    https://sntoom.net/how-long-do-dc-motor-brushes-last/

    One of the reasons that PM Motors are very popular with Solar Power Systems is the use of the VFD... Which is (again typically) a 3 phase Inverter (with DC or AC power input) and a 3 phase variable frequency output--This allows the VFD to vary the output frequency to the PM Motor based on actual needs... I.e., turn the motor slower when there is less sun (Morning or Evening, or poor sun/bad weather)--I.e., to harvest and use the available power of the solar array, instead of (for example) only running under full sun in middle of day, and/or oversizing the solar array to get more/better morning/evening/bad weather harvest).

    Also, the VFD controller can take other control inputs--Such as pump output pressure and water flow--And vary the pump RPM to meet the needs of the down stream water system.

    There are lots of variables here.... And I am not a solar pumping expert. Perhaps some reader(s) here can give you some guidance on your questions/needs.

    Our host, NAZ, does have sales engineers/support for water pumping... They would be a good start (not sure they support 8 HP pumping or not).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • JRHill
    JRHill Registered Users Posts: 465 ✭✭✭✭
    #4
    "There are lots of variables here..."

    Bill, that is an understatement deluxe.

    "I would like to know if any of y’all know of a submersible pump manufacturer that makes a pump strictly with a DC motor. "

    We have a Grundfos AC/DC pump for our water well. 16 years and nary a hiccup. It really doesn't care what you throw at it, AC or DC, reverse polarity, etc. if just figures it out and pumps. It just needs to be above a lower voltage (~45+) and not be higher than the upper limit (~280). It's not inexpensive though. If solar is low we just plug it into the generator. It is profoundly efficient. It is soft start. Seems the model I have works great to 200' head and they have some deeper spec'd units.

    But these are mainly household duty. When you get to 50 gpm you are into commercial stuff. And for commercial use you don't want to screw around, do you?
    Off Grid. Two systems: 1) 2925w panels, OB VFXR3648, FM80, FNDC, Victron BMV-712, Mate3s, 240 xformer, four SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. HF 4550, Miller Bobcat.
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  • SumPower
    SumPower Registered Users Posts: 120 ✭✭
    edited October 1 #5
    Sum Pumps Stafford AZ. Made in the USA

    DC submersible pumps. 


    Edit: They sell them in the store at NAZ.
     solar-electric.com

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