Motor Current calculation

AJITNAYAK
AJITNAYAK Registered Users Posts: 11 ✭
in General Solar Power Topics #1
Dear all,

I have small doubt in calculation & selection of proper motor

I have two application
1) Solar tracker : where i used below actuator which is rated 24v , 4A,500 rpm used to caary 800Kg load.

power =24*4=96w
torque=(0.096*9550)/500=1.833N-m
Here is motor will stop every 5 min

2) In another project., Air condition blower application with continuous operation, motor designed to carry 48v . 5A rated ,axial load and radial load can carry upto 10kg.
The power: P=5A*48V=240W
The torque: 0.24KW*9550/1550RPM=1.528Nm (PS: the torque you required before: 0.59 Nm) this is desired
But we want to run it for 2400 rpm
1.528NM*2400RPM/9550=0.384KW

because of change in wattage our stator got damage. bearing got disturb etc.

My question over here .
In first application we running motor almost 500 rpm carrying 800kg of load
where in second case we running motor 2400 rpm @48v and carry load of 900gm
I would like to why huge amount of current draw in above case??
what are points are doing in selection of motor???

in above case if we increase wattage of motor we can run motor.
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Comments

  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #2
    Re: Motor Current calculation

    In one place you wrote .5A and then you used 5A in the calculation. Also be sure to account for motor and drive efficiency and any gearing involved.

    Operating a motor at more that the rated wattage is generally a bad idea.

    I am available for custom hardware/firmware development

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Motor Current calculation

    I am really confused--The first is a linear actuator that "lifts" a 800 kG load on the order of 3 mm/second...

    And the other is driving a fan assembly that weighs a maximum of 0.9 kG that is balanced (no torque due to "moving" of 0.9 kG load)... The only torque is the result of moving air (and frictional losses of air/bearings). And, it appears that you are changing the RPM of the fan from 1,550 RPM to 2,400 RPM. Besides worrying about the maximum rated RPM of the fan (fly apart at higher speeds), that the increase in RPM will both increase torque (higher RPM means more air movement/drag) and increased power needs (higher RPM at same torque is more power).

    Sorry, this website is in English units (should be "American" units now?). But it gives you the basics on how to read fan/blower performance charts:

    http://www.greenheck.com/library/articles/10

    Completely unrelated applications/motion.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Motor Current calculation
    BB. wrote: »
    ...But it gives you the basics on how to read fan/blower performance charts:

    http://www.greenheck.com/library/articles/10

    -Bill
    Jonr,

    If you take nothing else from the rather dense article, look at the equation which shows that with other characteristics being held constant the power required to turn an axial fan will increase as the cube of the RPM.

    In your example, upping the speed from 1550 to 2400 will require 3.71 times as much power from the motor. It is not all surprising that it would draw close to four times the current and overheat or burn out depending on what sort of overcurrent protection you provide.
    SMA SB 3000, old BP panels.
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  • daveingeb
    daveingeb Registered Users Posts: 1
    #5
    Re: Motor Current calculation

    OK So I think I am on the right thread... How about pump motors?? I want to put my pool pump (1 3/4 HP) on a solar system such as the 2000 W Off grid system shown on the N Ariz website. I have no other wish than to run the pool pump 8 hr/ day in the Phoenix area. I see an 8 panel system that would appear to be just right for my pool electrical requirements but I see little conversations here concerning running pool pumps. Any probs with the inductive load?
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
    Re: Motor Current calculation
    daveingeb wrote: »
    OK So I think I am on the right thread... How about pump motors?? I want to put my pool pump (1 3/4 HP) on a solar system such as the 2000 W Off grid system shown on the N Ariz website. I have no other wish than to run the pool pump 8 hr/ day in the Phoenix area. I see an 8 panel system that would appear to be just right for my pool electrical requirements but I see little conversations here concerning running pool pumps. Any probs with the inductive load?

    Welcome to the forum, (maybe this should be a new thread)

    Before getting into the details, let me ask: do you have grid power available?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #7
    Re: Motor Current calculation

    Lorentz makes some direct panel to pool pump systems, it requires replacement of your pump and the addition of the panels and a controller.

    http://www.lorentz.de/en/products/solar-pool-pumps.html

    You might just be better off doing a grid tie with those panels.

    BTW I run my VFD pool pump 3-4 hours a day in the Phoenix area, crystal clear.
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