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Newton-meter to kW/HP conversion calculation...not making sense

I didn't read through all of your math but any formula that considers RPM has gotta be screwy.

Power is power...while you can play games with RPM to make it do different things, it doesn't change the power. And since amps/watts are power, that's all you really need.

What can affect the power consumption of a motor? Aside from the basic voltage/amp relationship, there are really only two remaining variables - power factor and efficiency.

For the amps of any 3 phase induction motor, it's KW divided by 1.73 x effcy x pf x voltage. That's it. Nothing else.


As for DC drives...they are dead technology. Dead. While some installations of AC motors with VFDs might have been improperly done, the writing has been on the wall a long time now...DC is dead. A properly engineered AC system is king.
Power is power as you say, whether Volts x Amps, torque x rotary velocity, pressure x flow rate. All relate to one another with some inefficiencies due to conversion of one form into the other. Formulas with RPM are not any screwier than the others, just used for different applications.
 
Power is power as you say, whether Volts x Amps, torque x rotary velocity, pressure x flow rate. All relate to one another with some inefficiencies due to conversion of one form into the other. Formulas with RPM are not any screwier than the others, just used for different applications.
They are screwy when talking about power conversion, when the power base is electricity, which it is in this case. Electricity doesn't care about RPM.
 
They are screwy when talking about power conversion, when the power base is electricity, which it is in this case. Electricity doesn't care about RPM.
Doesn't change the laws of physics. There is a direct relationship between electrical power supplied to a motor, torque generated and rotary velocity (rpm). Voltage and current produce the electromagnetic field that applies the force to generate torque in the motor. My job has involved at various times designing electro-mechanical actuators, electro-hydraulic systems and electromagnetic fuel injectors. One of my current projects includes the design of subsea electric thrusters. I constantly go back and forth with mechanical, hydraulic and electrical power conversion to size drives, mechanical drive elements and electric motors.
 
Based on nameplate - close enough to 14kW to call it 14kW . . . it is a European motor rated at 400V/50Hz so a 4-pole motor with 100RPM of slip at full torque - soft torque/current curve which is typical for crane duty.

An 11kW VFD would run that motor fine at a reduced rating.
 
Doesn't change the laws of physics. There is a direct relationship between electrical power supplied to a motor, torque generated and rotary velocity (rpm). Voltage and current produce the electromagnetic field that applies the force to generate torque in the motor. My job has involved at various times designing electro-mechanical actuators, electro-hydraulic systems and electromagnetic fuel injectors. One of my current projects includes the design of subsea electric thrusters. I constantly go back and forth with mechanical, hydraulic and electrical power conversion to size drives, mechanical drive elements and electric motors.
It doesn't matter what your job is, nor does it require a change in the laws of physics. The point is simple - RPM has no role in the conversion of electrical power into mechanical power. If you are really designing thrusters, you should know that.
 
Based on nameplate - close enough to 14kW to call it 14kW . . . it is a European motor rated at 400V/50Hz so a 4-pole motor with 100RPM of slip at full torque - soft torque/current curve which is typical for crane duty.
What exactly on the nameplate makes you think it's a 14kw (or very close to 14 kw) motor?

For what it's worth the hoist on this crane has a 15kw motor (with a dataplate that says its a 15kw motor) and it's about twice the overall diameter, twice the shaft diameter and easily 3-4x the weight of this slew motor. If this crane had a slew motor that was that close in size to the hoist motor it would be a significant outlier when compared with other similar cranes in the company's fleet.

This isn't really a question about what it will take VFD-wise to drive it - the VFD the factory fitted it with seems to work fine - more a question of why the math seems so far off when trying to calculate kw from the information the OEM saw fit to give us on this dataplate.
 
"RPM has no role in the conversion of electrical power into mechanical power."

Ah, you might want to read up on that.
Ah, you might want to read up on it. Look up the formula for conversion of amps into KW or HP. Nowhere will you see RPM. Power is power, speed is not power.

Let me guess....you are sure speed is a component of power, and the ONLY reason we don't all use 65,000RPM motors is the big boys of the International Canned Goods Conglomerate won't allow it.
 
" Look up the formula for conversion of amps into KW or HP."

The lookup might be the calculation of hp from rpm and torque as the input values. As in, torque delivered by an electric (or any other kind of) motor, at a specified rpm. You might learn something....
 
Unfortunately for you, this topic has nothing to do with the relationship between HP and torque and RPM....go back and read the OP's post as to what he's looking for. Power is power. RPM is playing games with power...but the power stays the same.

Moving any given load will require the SAME power. A 4000HP compressor will require 4000HP to drive it. How you get that 4000HP is up to you - but you're not gonna drive the 4000HP compressor with 2000HP just because you tinkered with RPM.
 
In any case ,the hoist motor is the large power draw on a fixed position crane ,and if you size the power draw to the hoist only,you will be correct .......the other power uses will be boom luffing or trolley and slew ....which generally are not used concurrently with the main hoist,or with each other....you can also add few watts for brake motors,although often the non hoist brakes are spring loaded automatic application.
 
What exactly on the nameplate makes you think it's a 14kw (or very close to 14 kw) motor?

For what it's worth the hoist on this crane has a 15kw motor (with a dataplate that says its a 15kw motor) and it's about twice the overall diameter, twice the shaft diameter and easily 3-4x the weight of this slew motor. If this crane had a slew motor that was that close in size to the hoist motor it would be a significant outlier when compared with other similar cranes in the company's fleet.

This isn't really a question about what it will take VFD-wise to drive it - the VFD the factory fitted it with seems to work fine - more a question of why the math seems so far off when trying to calculate kw from the information the OEM saw fit to give us on this dataplate.
1400 RPM @ 95 Nm is roughly 14kW all day long.

Using imperial units with common HP calculations . . .

95Nm x 8.85 In-lbs / Nm = 841 in-lbs
841 in-lbs / 12 in-lbs / ft-lb = 70 ft-lbs

1400 rpm X 70 ft-lbs / 5250 = 18.68 HP
18.68 HP x 0.746 kW / HP = 13.94 kW

Or roughly 14kW . . . derived using the queens mathematics derived from motor nameplate RPM and torque.

Since there is no current rating on the nameplate, all the fuss about RPM having nothing to do with the power rating displays a prideful bit of ignorant arrogance me thinks. Kudos to Jim Rozen for sticking to the facts.
 
There might not be a current rating on the nameplate, but the OP clearly mentions FLA as a go-by. Sticking to the facts? More like willful ignorance. Kudos to those who champion ignorance - the fuel of half our society.

Go look at a 5HP 900RPM motor, then look at a 5HP 36000RPM motor. The FLA will be different (a little) ONLY because of the difference in PF and Effcy - not because of the RPM.

You boys need to put down the pocket guides and learn how to comprehend what matters and what doesn't when discussing power conversion. Not power game playing. Power is power...for the 3rd time.
 
There might not be a current rating on the nameplate, but the OP clearly mentions FLA as a go-by. Sticking to the facts? More like willful ignorance. Kudos to those who champion ignorance - the fuel of half our society.

Go look at a 5HP 900RPM motor, then look at a 5HP 36000RPM motor. The FLA will be different (a little) ONLY because of the difference in PF and Effcy - not because of the RPM.

You boys need to put down the pocket guides and learn how to comprehend what matters and what doesn't when discussing power conversion. Not power game playing. Power is power...for the 3rd time.
The entire point of the original post is that no where on the motor nameplate or available documentation is the FLA to be found. In which case, you only have torque and RPM documented on the nameplate from which to calculate power.

Perhaps you missed that point - easy to do when scrolling through. If you are quick to discount the knowledge and experience of others, expect the same in response.
 
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