Electrical Motors - Heat Loss

Heat Loss from Electric Motors during Operation

Heat loss from electric motors due to inefficiency:  

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Electrical Motors - Heat Loss vs. Efficiency Size of Motor
(kW)Efficiency
(%)Heat Loss
(watts/kW) 0 - 2 75 250 3 - 15 85 150 15 - 150 90 100 150 - 92 80

• 1 kW = 1.34 hp
• 1 hp = 0.746 k W

Example - Heat Loss from an Electric Motor

The heat loss from an electric motor supplied with 10 kW can with the heat loss 150 watts/kW from the table above be calculated as

(10 kW) (150 watts/kW)

= watts

= 1.5 kW

The rest of the energy

For more information, please visit How Do Electric Cars Generate Heat.

(10 kW) - (1.5kW)

= 8.5 kW

is output mechanical energy. 

If the motor and the mechanical equipment connected to the motor is in the same room - or enclosure - all electric energy supplied to the motor will convert to heat and temperature increase in the room.

Heat Loss from an Electric Driven Device to a Room

The heat transferred to a room or enclosure depends on the location of the motor and the driven device related to the room. 

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1. motor and driven device in the room - all energy to the motor is at the end transferred to the room (heat loss from the motor and frictional energy from the driven device)
2. motor in the room and device outside the room - only heat loss from the motor is transferred to the room - frictional energy from the driven device is lost outside the room
3. motor outside the room and device inside the room - frictional loss from the driven device is transferred to the room - energy loss from the electric motor is lost outside the room

Electrical Motors - Heat Loss to Room Air Nameplate Rating
(hp)Motor Efficiency
(%) Heat Loss to Room Air
(Btu/hr per rated hp)
Motor in Room
Driven Device inside RoomMotor in Room
Driven Devise Outside RoomMotor Outside Room
Driven Device inside Room 0 - 1.5 0.80 508 1.5 - 12.5 0.85 381 12.5 - 0.90 254

• 1 Btu/h = 0.293 W 
• 1 horsepower = Btu/hr