Husen Rupani:
In this video, we will look at a direct online circuit with DC injection break. Let’s get started.

Hi, I’m Hus. In this video, we will look at a direct online circuit with DC injection braking using our control circuit and motor starter pracboxes. First, we’ll look at the circuit diagram and we’ll identify the components that we’ll use for the circuit and then connect and test the circuit. Let’s start with the circuit diagram.

Here’s a circuit diagram we will use for connecting the circuit. A quick disclaimer. As you might notice, I haven’t covered all the safety aspects of the circuit. I’ve just made it functional. Here’s our three-phase motor. Here are the contacts of our main contactor and this is the contact coil. Here is our contacts for the braking contactor and this is our coil for the braking contactor. Here is our on-delay timer and here’s our normally closed contact that we’ll use for that timer.

These two stop buttons are actually just one stop button. One side we’ll use normally open, other side we’ll use normally closed. And here’s our start button. And the one that I missed is this holding contact for this contactor coil. Let’s see how this circuit will work. When the start button is pressed, the current will go from L1, through stop push button, through start to coil K9, which will close this contact and create a holding circuit. So our current path will be here and then back to neutral, which will close these contacts and turn on our motor. So that’s our direct online circuit.

If we press this push button momentarily, it will turn off the motor, but won’t engage the braking. To engage the brake, we have to hold the push button for the braking to kick in. If we keep this push button held, this circuit will disconnect and the current will then start flowing through this circuit. When it’s flowing through this circuit, it will then go through this timer, which will then start counting the timer down. Since this is through normally closed, this coil will energize.

As soon as this coil energizes, these contacts will close, which will supply DC to the two windings and bring it out from the third winding here, which will essentially create DC injection braking. Now, we don’t want the DC injection braking to stay on all the time and that’s why we’re using this timer. As soon as this timer finishes counting, this will disconnect and the brake will turn off or this coil will disconnect and the brake will turn off. Let’s identify the components we will use and connect the circuits.

For this circuit, we’ll use Portaphase for our three-phase extra low voltage, so the power will come from this distro box. We will use this start button. And we’ll use this button as our stop button because we need NC and NO, both contacts. This will be our main contactor. This will be our braking contactor. We’ll use this timer, which is set to on delay and at three seconds. So after three seconds it will operate. We’ll use this DC power supply for braking and we’ll use this motor for our circuit. Let’s connect the circuit.

Now that our control circuit is complete, let’s test it. So our stop, start operation works. Start. Stop. Start. And what if we keep it pressed? We can see that this contactor stays on and after the time finishes, it turns off. Let’s now connect our motor and the braking power supply.

Now that our circuit is complete, let’s test the operation. So I’m going to turn on the DC power supply for our braking and turn on our power supply, the three-phase power supply. Let’s operate the motor. Start, the motor spins, which works. And if I press the stop momentarily, the motor stops without the brake engaging. Start again. This time I’m going to hold the push button or the stop push button to engage the braking. The timer will start counting down and the disc will stop almost immediately. And as soon as the timer is finished, this contactor will then disengage. That disengaged. So we know that our circuit works.

While I was connecting the circuit, I realized there was a main safety aspect that I missed. What if the main contactor and the braking contactor turned on at the same time? If that were to happen, then the AC power supply and the DC supply will interact and damage one or the other. So we need to put some sort of interlock in place. So let’s have a look at the circuit again.

So in this circuit, if I put a normally closed contact here from this coil and a normally closed contact here from this coil, then that will create an interlock, an electrical interlock, which will avoid both of those contactors to turn on at the same time. Let’s do that in our circuit. Let’s turn off the power supplier before we make changes to our circuit.

So at this stage, there are no interlocks in place, so we’re going to put an interlock. We’ll first put an interlock for the main contactor. So this is the old circuit that goes to the main contactor. We’re going to route it through a normally closed contact from the braking contactor. What that means is if the braking contactor is on, our main contactor can’t turn on and we’re going to do the other way around as well. So we’re going to take the A1 for the braking contactor and route that through the normally closed off our main contactor. So now we have an electrical interlock in place. Let’s turn on the power and test our circuit again.

When I turn on the motor, the motor turns on. Moment to repress, motor turns off, but the braking isn’t engaged. Let’s try and do that. This time we will keep the stop button pressed. And when we do that, we can see that the motor turned off, timer and our braking contactor then disconnected after the timer finished. I hope you enjoyed this video of direct online circuit with DC injection braking. If you have any questions or feedback, please feel free to contact us. Thanks for watching.