Click noise in power supply when turning PC on or off

It is quite common to see comments on the Internet from people who hear a click noise coming from the power supply when turning your PC on or off. The existence of this noise can give many the wrong idea that the source is faulty. But… if it is not a defect, why is this noise heard? In this article we will explain it to you.

Index of contents

The culprit for the noise is a simple electromechanical relay

As indicated above, this noise is produced by an electromechanical relay. This is a component that basically works like an electrically operated switch.

Animation of a working relay

This component basically consists of several metal contacts and an electromagnet. When current passes through the electromagnet, it attracts a metal sheet that tilts, pushing the two contacts, which work as a switch, making them touch and therefore closing said switch. As you can see, it is a very basic component.

And where does the click noise come from? Very easy! It is simply the noise of the contacts colliding. Absolutely all electromechanical relays make noise, although it is true that some are noisier than others.

What is the relay for in a power supply?

Relay and NTC in one source

In a power supply, a relay can have two fundamental uses.

In addition to an NTC thermistor

This is the main use that is given today. It should be noted that the relays are usually only in sources of medium-high range and higher, in the cheapest they are not normally present.

"Inrush current" (the current peaks we refer to) with and without an NTC thermistor.

To understand this use, the first thing is to explain what an NTC thermistor does. It is a resistance whose value varies depending on the temperature (high when the temperature is low and vice versa). When we use this thermistor, we limit the current peaks that occur when turning on the source and that are harmful.

Once the NTC has done its job, the relay is actuated so that the current passes through its contacts and not through the thermistor itself. In this way, two things are achieved:

The NTC cools down, so if we restart the equipment it will act effectively again.It prevents the NTC from consuming energy, thus increasing the efficiency of the power supply.

As we indicated previously, the relay is not usually seen in low-end sources, but seeing an NTC is very common.

To drive the 5VSB rail

For the record, this application of the relay is deprecated in today's sources, and this drive is regulated by transistors.

Basically, a power supply has two different 5V rails: the normal one, which is used when the source is running, and the 5VSB (5V Stand-by), which is always kept running when the equipment is turned off and the source connected to the current. The relay would be used to make the switch between 5V and 5VSB when turning the equipment on and off.

What if the click noise is heard constantly?

In case the noise that we describe is constantly heard during the operation of the source, then it is very possible that we are facing a defect. In many cases, this noise does not come from the relay but from the fan, since the motor can make a noise that sounds like a continuous “click”. If it's a subtle noise that's hard to hear, then chances are the fan itself is. If instead it is too obvious a noise, then surely it is defective. You can check if it is the fan by manually stopping it by putting an object between its blades with the source turned off and turning it on.

WE RECOMMEND YOU How to choose an SSD

www.youtube.com/watch?v=p0A-dxoFItQ

If we check that the noise does not come from the fan, as in the example case above, the fault may come from another component. In the case of the video, it seems that it is simply “coil whine”, a phenomenon that is not harmful, but still if it is as annoying and audible as in the video, most stores and manufacturers would accept an RMA from the source and a replacement for another.

In any case, we recommend that you contact the manufacturer of your power supply to diagnose the problem.

Final words and conclusion

We hope that this article has been useful for you to know that the click noise of a relay is completely normal and, incidentally, to learn a little more about the operation of power supplies.

Do not forget to take a look at our other articles on power supplies, we leave you some of them:

Also don't forget to leave all your doubts and suggestions in the comment box below?