USE OF A RELAY TO CONTROL TWO GROUPS OF LAMPS (PRACTICE)

—

Welcome to the home’s electrical systems course by NPR Online Technologies!

Buy our book here:

Before starting this lesson, we recommend that you subscribe to our youtube channel and visit all our lessons on our website.

In this practical lesson we will see how to use a single relay to control two lamps or two groups of lamps.

In the previous lesson, we have analyzed the four-state relay from a theoretical point of view.

We have also analyzed a typical relay-based circuit diagram.

We are therefore ready to proceed with the practical installation of the circuit that allows to control two bulbs by using a push-button and a four-state relay.

We observe that the coil of the relay that we will use in this tutorial must be powered with a nominal voltage of 230 V. Therefore we cannot power it with the 9 V battery.

For this reason we will use the 230 V alternating current voltage of the electrical system of our homes in order to power the coil.

It is therefore important to note that, even though it is a very simple practical session, the circuit will work with voltage values that can cause very dangerous electric shocks. For this reason, this installation must be conducted with the utmost caution and with the presence of an electrical system expert. In any case, it is absolutely forbidden to have this exercise performed by non-adults.

Before proceeding with the assembly of the circuit, let’s briefly recall its operating principle.

First of all we can observe that the four-state relay has two switches.

The two switches are connected to the two lamps (or groups of lamps) to be controlled.

The push-button is connected to the hot wire and, when it is pressed, it creates electrical continuity of the hot wire with the relay coil.

When this happens, the coil commands the two relay switches. In our example, the two switches are then closed. In this way, both lamps light up

and remain on, even when the button is released.

If we press the button a second time, the coil opens the first switch of the relay and consequently the corresponding lamp turns off,

 and remains off even when the button is released.

If we press the button a third time, the coil closes the second switch and simultaneously opens the first switch, thus reversing the previous situation.

In particular, we have that the lamp that was off turns on, and the lamp that was on turns off.

Finally, by pressing the button a fourth time, the coil opens both switches, and consequently both lamps will be turned off,

and remain so even when the button is released.

At this point the switching sequence can begin again.

We have already observed that in the practical circuit we are going to make, the coil will be powered at 230 V.

However, as shown in the following diagram, the circuit that powers the bulbs can be decoupled from the coil supply circuit.

we can therefore continue to work with our battery,

and the 12 V bulbs.

Before starting with the installation of the circuit, we can point out that the the push-button has been connected to the hot wire.

However, many relay manufacturers propose a connection of the push-button to the neutral wire as shown in the following diagram.

It is evident that from the point of view of the circuit operation, there are no particular differences; however, it is advisable to inquire about the regulations in force in the geographic region where the electrical system is being installed. In our tutorial we will adopt this second circuit solution.

We will adopt this solution because it is the one proposed by the manufacturer of the relay that we will use in our tutorial.

Well, having made these premises, we are ready for the practical realization of the circuit.

Buy our book:

—

The realization of this circuit starts from the circuit analyzed in the previous practical lesson where we have worked with the push-button.

With reference to this circuit, we open the junction box,

cut a piece of flexible tube of about 30 centimeters

and insert it into the left hole of the junction box.

In this tube we insert a brown wire and a blue wire

that are connected to an electric plug.

We can take the electric plug already mounted in a previous tutorial. We will use this plug to connect the brown and blue wires to the 230V AC voltage.

In the junction box we can therefore distinguish the wires coming from the 9 V battery,  and the wires coming from the 230 V AC.

Let’s see a detail in this zoom.

In the photo we can also recognize the relay that we will use in this tutorial.

We can now proceed by cutting a second flexible tube of about 30 centimeters that is inserted into the hole at the bottom of the junction box. We will use it to bring the wires from the junction box to the two bulbs.

On the right we see the electrical box with the push-button already inserted in the appropriate support.

As for the button, two blue wires have already been cut, which must be connected to the two terminals of the push-button as indicated by the circuit.

We can see that the two blue wires pass through the electric tube and come out of the junction box.

At this point we can proceed by inserting the relay inside the junction box.

We can also make the first connections,

in accordance with the following circuit diagram.

We can see that the brown wire which is connected to the hot wire of the electrical system is connected to the relay coil. The other contact of the relay coil is connected to one of the two contacts of the button by using a blue wire.

The other contact of the button is connected to the neutral wire of the electrical system.

For this last connection we use a screw terminal.

At this point the circuit that powers the coil has been completed.

We recall that this part of the circuit will work at 230 Volts.

We can now proceed by connecting the bulbs.

We prepare two brown wires and two blue wires with a length of about 30 centimeters,

and insert them in the tube that leads from the junction box to the two bulbs.

We connect the pairs of wires to the two bulbs using the appropriate screw terminals.

The two pairs of wires connected to the bulbs are also available in the junction box.

The following wiring diagram indicates that the brown wires coming from the light bulbs, must be connected to the two internal switches of the relay,

by means of the appropriate relay terminals.

The blue wires coming from the light bulbs

must be connected to the negative pole of the 9 V battery (which by convention we assume as the neutral of our electrical system).

This connection is made by inserting both cables into the appropriate hole in the terminal shown in the following figure.

We must now make the connections from the positive pole of the 9 V battery (which we assume by our convention as the hot wire of our electrical system). To do this, we cut two short pieces of brown wire and join them together on one side.

The ends of the wires that have been joined must be inserted into the appropriate hole in the screw terminal shown in the following figure.

The other end of the two brown wires must be connected to the two relay switches,

just as indicated by the following electrical circuit.

This is the last connection to be made, and we can proceed by closing the junction box.

In this photo we can see the final appearance of the circuit.

We can also easily find matches with the circuit diagram.

We are therefore ready to proceed with the test of the operation of the system.

We must remember that this circuit will work with a voltage of 230 Volts and, for this reason, we have indicated a red triangle on the work plan right in correspondence with the electrical plug that we will use to power the circuit.

Well, in the presence of an expert in electrical systems and in the absence of children, we can connect the plug to the socket.

From this moment on, it is necessary to pay the utmost attention, avoiding touching any part connected to 230 Volts.

Before starting the electrical system test, a doubt may arise: in which position of the electrical socket is the hot wire?

Is it connected to the top or bottom contact of the socket?

To establish this we should open the socket and check the color of the wires connected to it or, much better, we should use a testing screwdriver. For the purposes of this tutorial we will ignore these aspects and connect the plug without considering the problem of the real position of the hot wire.

This does not pose any problems in our exercise. The only situation that could occur is that the push-button will be connected to the hot wire and not to the neutral wire, but for the purposes of this tutorial this does not represent any problem.

Well, at this point we are ready to test the system.

We will observe that pushing the button several times we start the switching sequence of the relay. First we have both light bulbs on, then only the left light bulb remains on, then only the right light bulb is on and finally both light bulbs will be turned off. As we have already pointed out other times, when both bulbs are on, their brightness is reduced due to the fact that we are using a 9 V battery that is unable to deliver the necessary voltage and power to allow both light bulbs to turn on with the maximum brightness. Clearly this is a problem related to our particular implementation and does not occur in real electrical systems.

The switching sequence is also described in the relay datasheet. In particular, we are using the finder 26.04 type, which as indicated in the datasheet, starts from a condition in which both switches are open (and therefore the lamps are off) to continue with the condition in which both switches are closed (and therefore the lamps are on), then the sequence continues with the other two states in which one switch is open and the other one is closed.

On the same datasheet it is proposed a circuit diagram which, as you can see, is the same implemented in our tutorial.

—

We conclude this tutorial by showing how the four-state relay can be easily turned into a two-state relay. Basically, we want to downgrade the 26.04 to 26.01 type.

To do that, it is sufficient to use only one of the two relay switches.

In our case we have to identify the switch that changes state each time the button is pressed.

In our relay, in fact, only one of the two switches is able to change state each time the button is pressed.

More specifically, in the case of our system, it is the switch that controls the right light bulb.

For that reason, we disconnect the left light bulb and with this modification, each time the button is pressed, we are able to alternately switch the right light bulb on and off, just like it would occur in the case of a two-state relay.

We point out that instead of a single lamp we can have a group of lamps connected in parallel.

Well, we have come to the end of this lesson dedicated to the to use of a single relay to control two groups of lamps.

We suggest you immediately consolidate the concepts you have just learned by carefully reviewing this lesson and above all by going through all videos of our course, by accessing our playlists.

We remind you that our website is active with numerous insights on these issues.

We also suggest some useful actions that will undoubtedly contribute to the growth of this channel: in particular, we invite you to send us your comments, to like our videos and share them with your friends.

Finally, don’t forget to subscribe to our youtube channel to stay up to date on all our activities.

Thanks for your attention and … see you next time!

GO TO THE MAIN PAGE OF THE COURSE (FULL LIST OF LESSONS)…

Buy our book:

—