• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Speed control for a 3 phase motor?

Not open for further replies.

ed sparks

New Member
Can I have a cheep alternative to a motor drive. I need to control the speed of a 3 phase, 1.5Hp, 63 output rpm, 460Vac motor. Please Help, My boss is cheap.


Active Member
There is no cheap method to control speed of AC motors. The speed eq. of AC motor is :
S = 120 * F / P

Where F = AC signal Frequency & P = No. of Poles in motor
Thus speed depends on F and P
But P is constant for given motor
Thus speed can only be controlled by varying the frequency.
For 3-phase motor, you require a 3-phase variable frequency PWM generator (you can use microcontroller). This PWM signal needs to be linearly amplified to get approximate AC output for motor which can either be done using MOSFETs or IGBT (more prefered).
All these are minimum requirements of AC drives which won't come cheap.
Not open for further replies.

Latest threads

EE World Online Articles