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I am working on a project in which i need to connect Permanent Split Capacitor(PSC) AC motor using relays as shown in the below block diag fig 1. I want to rotate it in both CW and CCW direction. It is a 30W AC motor. But on googling some data i found the image as shown below fig 2, whihc show only one swich which will toggle to change the capactior polarity, to change the direction of the motor. Can i do the interface using one realy only or if i want to do the conection using two relays than how it can be done? Please correct me if i am wrong.

Fig 1

Fig 2

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    \$\begingroup\$ Are you going to make provisions to wait for the motor to stop before reversing? \$\endgroup\$ Jul 29, 2014 at 6:32
  • \$\begingroup\$ this motor will act as a mixing motor,will rotate in both direction without stopping in bwt for fixed period of time and then come to stop state. \$\endgroup\$
    – user39551
    Jul 29, 2014 at 6:56
  • \$\begingroup\$ Do you have a wiring diagram for your PSC? Not all PSC's are able to be reversed like your second figure. \$\endgroup\$
    – Eric
    Jul 29, 2014 at 12:11
  • \$\begingroup\$ No, i dont have wiring diagram. :( Till now part number is also not decided still working on it, but the motor will be PSC 120VAC and 30W rating. \$\endgroup\$
    – user39551
    Jul 30, 2014 at 5:02

1 Answer 1

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All permanent split capacitor (PSC) induction motors are connected as shown in the picture below.

Figure 1 - PSC

I added 4 colors to indicate each end of the main and auxiliary windings. Most PSC motors come with either 3 wires or 4 wires exiting the motor. For 4 wire PSC motors, the yellow, green, red, and blue wires exit the motor. Then they can be connected to the capacitor and power source as shown. Typically the main and auxiliary windings in a 4 wire PSC will be different (that is, they will have different number of turns, different wire gauge, etc.). That means that to reverse a 4 wire PSC, you need to switch the yellow and green leads around. This reverses the polarity of the main winding and causes the motor to reverse.

For 3 wire PSC motors, the main and auxiliary windings are identical (same number of turns, same wire gauge, but they are placed in different stator slots). Usually the red and green wires are connected internally so that only one wire exits the motor. When this is the case, the 3 wire PSC can be reversed in the same way as your second figure above. In my picture the switch would be in parallel with the capacitor and switch between the yellow and blue leads. This works because the main and auxiliary windings are identical and you are causing the main winding to lead or lag the auxiliary winding by switching.

3 wire PSC motors can be reversed with a single pole/double throw switch to reverse. 4 wire PSC motors require a triple pole/double throw switch to reverse.

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