Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

# Electrical Motors - Shaft Power vs. Voltage and Current

## Calculate electric motors shaft power.

Power is in general rated in watt (W) or horsepower (hp) . The old imperial unit horsepower is equal to 746 watts (0.745 kW) or 33000 lb ft per minute (or 550 lb ft per second ).

The unit of electric power - 1 watt - is equal to the power produced by an electrical current of 1 amp at a potential difference of 1 volt .

• 1 watt = 1 / 746 hp
• 1 hp = 746 watts = 0.76 kW

### Shaft Power in watts

#### Direct Current - DC

Shaft power produced from a direct current (DC) electrical motor:

P shaft_kW = ηm U I / 1000                      (1)

where

P shaft_kW = shaft power (kW)

ηm = motor efficiency

U = voltage (V)

I = current (A, amps)

#### Alternating Current - AC

Shaft power produced from an alternating current (AC) electrical motor:

##### Single Phase

P shaft_kW = ηm U I PF / 1000               (1b)

where

PF = Power Factor

##### Two Phase Four Wire

P shaft_kW = ηm 2 U I PF / 1000                  (1c)

##### Three Phase

P shaft_kW = ηm 1.73 U I PF / 1000                  (1d)

### Shaft Power in hp

Shaft power as horse power :

P shaft_hp = P shaft_kW / 0.746 (2)

or for a DC motor

P shaft_hp = (ηm U I / 1000) / 0.746

= ηm U I / 746 (2b)

where

P shaft_hp = shaft power (hp)

#### Example - Shaft Power Electric Motor

The shaft power produced by an electric direct current motor with 36 V, 85% efficiency and 5 amps - can be calculated in watts as

P shaft_kW = 0.85 (36 V) (5 amps) / 1000

= 0.153 kW

= 153 W

The shaft power as hp

P shaft_hp = (0.153 kW) / 0.746

= 0.21 hp

### Standard Horsepower Ratings

Standard horsepower ratings for electrical motors - 1 to 4000 hp are indicated below:

• 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1250, 1500, 1750, 2000, 2250, 2500, 3000, 3500, 4000

Nominal voltage of not more than 600 V AC and nominal frequency 50 or 60 Hz .

## Related Topics

• ### Electrical

Electrical engineering with units, amps and electrical wiring. Wire gauges, electrical formulas, motors and more.

## Related Documents

• ### Asynchronous Induction Motors - Electrical Properties

Typical electrical motor data like nominal current, fuse, start ampere, size of contactor and circuit breaker - for asynchronous induction motors.
• ### Electric Motors - 480 Volt Wiring

480V electrical motor wiring data - NEMA amps, starter size, HMCP size for motors ranging 1/2 to 500 hp.
• ### Electrical Induction Motors - Synchronous Speed

Operating speed of an induction motor depends on the input power frequency and the number of magnetic poles in the motor.
• ### Electrical Motors - Frame Dimensions

Electrical motors NEMA frame dimensions.
• ### Electrical Motors - Horsepower vs. Voltage and Amps

Electrical motors horsepower rating vs. their ampere rating.
• ### Electrical Motors - Insulation Classes

Electrical motors NEMA temperature and insulation classes.
• ### Electrical Motors - Locked Rotor Design Code Letters

NEMA locked rotor indicating code letters for electrical motors.
• ### Electrical Motors - Starting Devices

Direct-on-line starters, star-delta starters, frequency drives and soft starters.
• ### Electrical Vehicle Charging - Power vs. Voltage and Amps

EV Charging - AC vs. DC, single phase vs. three phase and power vs. voltage and amps.
• ### Fan Motors - Starting Torques

The motor must be capable of accelerating the fan wheel to it's operating speed.
• ### Heat Gain from Electrical Motors in Continuous Operation

Amount of heat transferred from electrical motor to ambient room vs. locations of fan and motor.
• ### Nema Starters

Nema sized contactors or starters.
• ### Power

Power is the rate at which work is done or energy converted.
• ### Pump Power Calculator

Calculate pumps hydraulic and shaft power.
• ### Pumps, Fans and Turbines - Horsepower

British Horse Power as used for pumps, fans and turbines - and how to convert to other units.
• ### Single Phase Power Equations

Power equations for single phased electrical systems.
• ### Three-Phase Power - Equations

Electrical 3-phase equations.

## Search

Search is the most efficient way to navigate the Engineering ToolBox.

## Engineering ToolBox - SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .

## Citation

• The Engineering ToolBox (2004). Electrical Motors - Shaft Power vs. Voltage and Current. [online] Available at: https://www.engineeringtoolbox.com/electrical-motor-horsepower-d_653.html [Accessed Day Month Year].

Modify the access date according your visit.

6.3.17

.