# induction motor with constant speed.

Discussion in 'The Projects Forum' started by onlyvinod56, Oct 14, 2008.

1. ### onlyvinod56 Thread Starter AAC Fanatic!

Oct 14, 2008
362
1
Hi,
this is vinod. In my text book i found a block diagram to implement constant speed control for induction motor, by comparing the motor speed with a ref speed . and the error signal is used to vary the firing angle for triac which controls the line voltage and hence the speed.

my question is, if the motor is having 230v 1500rpm as rated conditions,
the required speed is 1200rpm,,,,,so, the voltage(230v) has to decrease to get 1200rpm. Let the voltage be 180v. If my required speed is say 700rpm,
I think, i cant reduce the voltage. Can anybody fix this problem? If i still reduce the voltage, what will happen to the motor?

2. ### Audioguru Expert

Dec 20, 2007
11,231
1,334
An induction motor's speed is contolled by its number of poles and by the frequency of the AC.
A universal motor's speed is controlled by its average voltage (by a light dimmer that has a triac).

Maybe you have a 60Hz induction motor but have a 50Hz mains frequency.

It will be difficult to build an oscillator to drive a power amplifier and rectify the mains into DC to operate them.

3. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
It can be done with pulleys and belts. Select pulley diameters that give you the correct resultant speed.

4. ### vetterick Active Member

Aug 11, 2008
35
0
Lets see here you have a 1500 RPM motor, that would be a 4 pole at 50 Hz, you could get a 1000 RPM motor (6 pole), if you had 60 Hz you could run the 6 pole at 1200, nope I think your out of luck.

Beenthere, how dare you suggest such a simple and effective solution, if it dosn't use a couple of PICs a programming degree and a handfull of other devices they dont seem to like it here.

All kidding aside a mechanical solution is the easiest.

5. ### thingmaker3 Retired Moderator

May 16, 2005
5,073
8
I'm sure Beenthere intended a PIC-controlled group of linear armature stepper motors to move the belt to different pulleys.