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What's the difference between a 1HP and 2HP electric motor?

Slightly different dimensions: Diagram

They look almost identical:
0.75kW, 1HP
1.50 kW, 2HP

Here are the specs:
Specifications
Specifications

Same top speed (RPM). Same Voltage. Difference in current required. What is physically different between the two? What causes one to draw more current than the other? Is it simply more winds on the coil? Thicker gauge wire? Larger stator/rotor? How is it they have the same max RPM? Shouldn't more power mean higher speed in the absence of other variables (e.g. weight)? What is the extra current spent on if not speed? Torque? Or is the extra current only drawn under load; in response to a physical resistance (i.e. drag) on the driveshaft?

These might seem like seperate, unrelated questions but really im just trying to determine: what's the same, what's different; and to understand: why.

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  • \$\begingroup\$ Those motors have a rotation speed synchronous to the mains frequency less nominal slip. \$\endgroup\$ – Chris Stratton Sep 13 '20 at 20:58
  • \$\begingroup\$ Which model numbers are they? \$\endgroup\$ – Bruce Abbott Sep 13 '20 at 21:02
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    \$\begingroup\$ @voices: Despite the similarity in the photos, the 2 hp motor is bigger than the 1 hp motor. Check page 25 and compare the size of the 80 frame to the size of the 90 frame. \$\endgroup\$ – JRE Sep 13 '20 at 21:18
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    \$\begingroup\$ Electrical current drawn by the motor, is roughly proportional to the mechanical torque required by the load. The 2Hp motor is capable of driving a load with more torque, at the cost of requiring more input power. The design of the rotor and stator (not visible in the photos) is what provides the capability for more torque, at the cost of more current. \$\endgroup\$ – MarkU Sep 13 '20 at 21:23
  • \$\begingroup\$ the prior answers seem to be correct. the main difference is a different characteristic of the coils. we can assume slightly increased wire diameter on the stronger motor to cope with higher current. More current then results in higher torque. \$\endgroup\$ – schnedan Sep 13 '20 at 22:51
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Same top speed (RPM).

Those induction motors have speed dependent on the incoming mains frequency, so they will be nominally the same, regardless of rated power

Same Voltage.

They are intended to run from the same voltage.

Difference in current required. What is physically different between the two? What causes one to draw more current than the other? Is it simply more winds on the coil? Thicker gauge wire?

Probably a different number of turns on the stator, which might require a different guage wire.

Larger stator/rotor?

Any given frame size motor will likely use the same diameter rotor. You have a frame 80 and frame 90 motor there, so they will be slightly different.

How is it they have the same max RPM?

Their max rpm, under no load, will approach 1500 rpm, this is the synchronous speed with a 50 Hz mains frequency.

Shouldn't more power mean higher speed in the absence of other variables (e.g. weight)? What is the extra current spent on if not speed? Torque? Or is the extra current only drawn under load; in response to a physical resistance (i.e. drag) on the driveshaft?

Speed is nominally constant, due to the AC frequency being constant, so the other variable, torque, changes. 'Slip' is defined as the % reduction in speed below synchronous. The current drawn by the motor is more or less proportional to the slip. As the motor load increases, the speed will drop, the slip increases, the current and so torque increases, until it reaches the rated speed of 1440 rpm at the rated power, either 1 or 2 hp depending on the motor.

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HP = Torque x 5250 / RPM, so given that it will be the same RPM at the same frequency, it's really just the torque that is different here.

The physical differences that lead to the motor being capable of developing more torque, and thereby more HP, come from the windings in the stator. Current is what generates torque and resistance and impedance are what control current. So to reduce the resistance, they use larger conductors and to reduce the impedance they use fewer turns in the coils. In some sizes that can be accommodated within the existing mechanical structure, but at some point it requires changing the depth and shape of the slots in the stator frame that the coils fit into. So once you get to a point of less resistance / inductance, more current flows in the motor and it produces more torque.

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