I put out a bit of a teaser a while ago for this post so it’s time to make it available. You will no doubt have some fun with this one although it is not a commonly used circuit as most applications use three phase motors
This circuit may seem a little bit daunting at first, but once you have worked your way through it you will notice it is quite simple. The most important thing here is the power circuit. You will note that I have made use of four contactors here. The reason is that we need five switching contacts for this circuit.
Following the power circuit in the Forward mode, contactors Q1 and Q2, you will see the following:
We have the Active/Live coming in on terminal 1 of the first contactor. When activated/energised, this will provide power to one side of the capacitor as well as one side of the running winding. Terminals 2 and 4 are connected to the other side of the capacitor and one side of the start winding respectively. Note the bridge across terminals 3 and 5
On contactor Q2, we have the Neutral on terminal 1 and 3. That then closes the loop to the other side of both the start and run windings when activated. The motor now runs in the forward direction. For us to change the direction, contactors Q3 and Q4, we will change the start winding around as follows:
We have again connected the Active/Live to terminal 1 of the first contactor for the reverse side, but the bridge we had from terminal 3 to 5 has now changed. We bridge from terminal 3 of Q3 to terminal 1 of Q4. Also note that our Neutral now comes in on terminal 3 of Q4 and is bridged to terminal 5 of Q3.
If you follow the motor connections now, you will note that we have swapped the start winding around with the rest of the connections still the same. Your motor now runs in reverse
For the control circuit, it is still the same principal as for the three phase forward reverse apart from the fact that I use two interlocking contacts from both the forward and reverse contactors and you will also note that I have used two contacts in series for the retaining contacts in parallel to the start buttons. Reason for this is that I want to be sure both contactors are activated.
Have a bit of a look at the circuit and let me know if you have any questions.
Till next time, stay safe!