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# What is the power of a battery required to run a motor of 2750 rpm motor? Answered

Pls tell me the power of a battery with which a motor of 2750 rpm motor runs?
What exactly will be the weight of that battery?

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1.5V with a micro motor.
A button cell will let it sping for about 5min, a D-cel battery for a few days.
A 3-phase industrial motor will require a motor drive (frequncy converter) and inverter and of course some decent batteries.
Run time depends on the quality of the electronics and how efficient they are plus power of the motor and how many AH are in the batteries to supply enough juice to the inverter.
The exact weight of the battery or batteries is between 2.4grams and a few metric tons.

I like this answer for the mass of the battery. 2.4e0 g to 2.4e6 g. That's six orders of magnitude, and probably a good estimate given what we don't know about the motor.

A master of eloquence are you !

Allow me to counterpoise with an eartbound single HP that uses ATP which has no need of crud electrical energy, volatile fuels or potential mechanical energy :-)

Well that's interesting: A horse driving a treadmill, driving wheels, pushing rubber against the road.

I think I might have seen, or read about something similar for marine propulsion.

You know, the easy way to do that, is you build a straight canal, with a horse path running parallel to the canal. Then the horses walk on the path beside the canal, pulling on a rope connected to a boat in the canal.

But there were other designs, designs that put the horses on the boat, and coupled the motion of their legs to giant paddle-wheels.

The attached images were found via Google(r) Image search for "horse powered boat"

Agree, those horse drawn canal boats were a historical reality before trains in the early times..

Not enough information really. The motor will have a voltage rating and should have a no load speed for that voltage.

What exactly is the weight of your motor ??

Physical power is usually, maybe always, the product of two numbers.

Two obvious examples, meaningful to your query, come to mind: Mechanical power in a rotating shaft, and electrical power supplied by a battery.

Mechanical power, in a rotating shaft, is the product of torque and speed.

P = tau*omega

(where tau is torque in newton*meters, omega is angular speed in radians/second, and P is in watts)

Electrical power, supplied by a battery, is the product of voltage and current.

P = V*I
(where V is voltage in volts, I is current in amperes, and P is in watts)

Where I am going with this story, is, that a quote for the speed of a motor (in units of RPM, rad/s, etc), that number alone, does not tell us how powerful the motor is.

Supposing you want to tell your friends how powerful a motor is, you start with the three variables in P=tau*omega. Then pick any two of them, i.e.

(tau and omega) or (tau and P) or (omega and P)
(torque and speed) or (torque and power) or (speed and power)

It seems to me the usual way is (speed and power). For example, I have an old band saw, and its motor has a nameplate, with some text on it that says, "H.P. [1/2] R.P.M [1725]" It says some other stuff too, so for the sake of show-and-tell, I'll attach a picture of this plate.

In honest SI units that translates to:

P = 0.5 horsepower * (746 W/hp) = 373 watts

omega = 1725 RPM * (2*pi/rev)*(1 m/60 s) = 180.64 radians/second

Just for fun I can use that equation to solve for torque, tau = P/omega

(373 W)/(180.64 rad/s) = 2.065 N*m = 2.065 newton*meters

To sort of tell the same story for electrical power, I claim, a quote about the voltage of a battery, just that one number, is not enough information to tell us how powerful that battery is. To specify how much power a battery can supply, recall: P = V*I.

So a quote about battery voltage V (measured in volts), and current I (measured in amperes) does say something about power, since P = V*I

In summary, when specifying power:

Two numbers: GOOOOOOOOOOD!

Well, that's kind of an oversimplification, and strangely reminiscent of that novel, Animal Farm, but it is like I said at the beginning:

Physical power is usually, maybe always, the product of two numbers.

Regarding the size of your battery, there's some mojo-juju called specific energy, and also specific power, for to calculate the mass (e.g. in kilograms) of your battery.