# Desk fan makes screen flicker

#### Blibo_baggins

Joined Sep 2, 2019
6
I have a 40w desk fan.

It has an analogue turn switch to turn on and change speed settings. Photo:

I currently have two displays. An old Dell 1703FTP and a Samsung P2450h from 2010~.

The Samsung flickers when I change speed in either direction and when turning on. The screen shows 'HDMI' after it recovers from the flicker on/off.
It ALSO causes my speakers to make a kinda pop sound.

There are 2 types of flicker that happen. One is juddering of the image on screen.

The second is the display is lost with a flicker, then a second or so later comes back again with the screen saying 'HDMI', like as if it only just detected the input.

I can also dictate which type will happen for the most part. If I turn the switch on the fan slowly then the second type of flicker occurs (loss of display for a second or so).

The Dell display is unaffected by this.

> Why is the Dell not affected?

> Why is this happening to the Samsung screen?

I tested it with 2 other fans. One has a digital control (a digital on/off switch with a bunch of other buttons for various modes and functions), and the other has the same type of analogue switch present on my fan.

- The digital fan causes no flickering at all AND no speaker pop sound.

- The other analogue fan causes the EXACT same issues only even more juddering and the speaker pop sound.

Speakers are Logitech Z5500.

Digital fan

Other analogue fan

EDIT: Tested on another socket in my room (same room) and the same issue occurs.

Joined Jul 18, 2013
23,619
The 'analogue' fans are Triac phase angle control, they may not have any suppression components, also the fans are most likely on the same circuit as the monitors.
Max.

#### Blibo_baggins

Joined Sep 2, 2019
6
The 'analogue' fans are Triac phase angle control, they may not have any suppression components, also the fans are most likely on the same circuit as the monitors.
Max.
Ok.... but that doesn't help me. I do not have electronic knowledge. Will this damage my PC components and other things such as my PC screen and speakers?

Why does this type of switch cause this issue?

Joined Jul 18, 2013
23,619
I doubt it will do damage, as I mentioned, the variable control fans are switched by a Triac 'dimmer' style method, which is a form of chopping the incoming AC.
If no suppression is used, they can radiate when controlling an inductive device particularly.
Max.

#### Blibo_baggins

Joined Sep 2, 2019
6
But you aren't answering why it's causing the screen to flicker - and only ONE of them as I wrote in my OP.

What is radiate in this context and inductive device?

No idea what all this suppression, triac etc and cutting AC means.

Thanks

#### AlbertHall

Joined Jun 4, 2014
11,504
Maybe one of them has a better power supply than the other and isn't affected by the interference from the fan.

Joined Jul 18, 2013
23,619
But you aren't answering why it's causing the screen to flicker - and only ONE of them as I wrote in my OP.
What is radiate in this context and inductive device?
No idea what all this suppression, triac etc and cutting AC means.
It is hard to answer a question that requires a technical answer when as you say, you have no idea what the answer means!
Max.

#### Blibo_baggins

Joined Sep 2, 2019
6
It is hard to answer a question that requires a technical answer when as you say, you have no idea what the answer means!
Max.
Hmmm wonder how teachers teach then. Nope guess everyone is just born understanding.

Joined Jul 18, 2013
23,619
First, what do you want to achieve?
Your question was 'why the flicker'? and an answer was attempted as to why.
Where do you want to go from here, eliminate the flicker?
Max.

#### Blibo_baggins

Joined Sep 2, 2019
6
First, what do you want to achieve?
Your question was 'why the flicker'? and an answer was attempted as to why.
Where do you want to go from here, eliminate the flicker?
Max.
> Why is the Dell not affected?

> Why is this happening to the Samsung screen?

> Why do my PC speakers pop?

You said you DOUBT it will do damage, so... you aren't sure. So why the doubt?

Joined Jul 18, 2013
23,619
Each piece of manufacturers devices are produced with some, often many, different designs, some can be affected by external electrical interference, others not so much, in your case, it also could be aggravated by all on the same AC circuit line.
I am not sure because I am analyzing from a distance and without some definitive testing it is very hard to in turn give a definitive answer as to what is happening, hence the educated guess.
Also the first hand experience with some Triac designed fan controllers that can cause interference with other equipment due to short comings in the design. Buzz in audio equipment for e.g.
Max.

Joined Jan 15, 2015
6,061
> Why is the Dell not affected?

> Why is this happening to the Samsung screen?

> Why do my PC speakers pop?

You said you DOUBT it will do damage, so... you aren't sure. So why the doubt?
Without seeing things and being able to actually look at the power lines using a device to monitor power line quality (power line analyzer) my best guess is The Dell monitor has better incoming power line filtering and a better power supply which is rejecting the noise or line spikes caused by the fan's speed control system. Less being able to see how exactly the fan controls speed everything becomes a best guess scenario. That is about as good as it gets without actually seeing things and being able to do a line power analysis of the power feeding the monitors and audio amplifier.

Hmmm wonder how teachers teach then. Nope guess everyone is just born understanding.

While that is quite true in the field of electrical engineering (electronics) the material Max posted is maybe about 3rd year material and now well understood less the first few years of basics. Making it simple, as simple as possible, the method the fan uses to control speed, the speed of an AC motor, has a bi product of noise, a large amount of noise. This noise can be fed back into the AC power line. How well other devices like monitors or any other electronics can filter out that noise is a function of their design.

How to fix it? The logical solution would be to buy a good line power conditioner. These can cost from $100 USD to$1,000 and higher depending on the actual needs which is impossible to determine without knowing exactly what is going on and doing an AC line power analysis. The problem becomes there is no simple way to answer your question. I have really over simplified things.

Ron

#### ElectricSpidey

Joined Dec 2, 2017
1,801
Every single “analog” multi speed fan I have ever owned used multiple motor windings to control the speed.

Joined Jan 15, 2015
6,061
Every single “analog” multi speed fan I have ever owned used multiple motor windings to control the speed.
I have one running above my head which uses capacitors.

I have also seen Triac circuits used and lastly switching in and out motor winding to control fan speeds. The ones using a triac are most likely the ones which generate the most noise. Regardless my money is on the fan motor placing noise on the AC mains. The quick and simple solutions are buy a better quality fan and hope for the best. Try running the fan on a different branch circuit of the load center and lastly buying a good quality line conditioner which can handle all the sensitive electronics on the AC mains line.

Ron

Joined Jul 18, 2013
23,619
Every single “analog” multi speed fan I have ever owned used multiple motor windings to control the speed.
I have three, all using Triac control.
Max.

#### Tonyr1084

Joined Sep 24, 2015
6,264
Cheap fans are noisy (electronically speaking).
Cheap power supplies don't filter the noise as well.

A monitor using a power supply that doesn't filter out noise as well can be affected by other equipment on the same circuit - as Max mentioned. Just plugging the fan into a different outlet in the room doesn't mean it's on a different circuit. Your breaker box has two lines coming in. Between the two lines is 240 volts AC. That power is split into two separate legs of power, typically referred to as L1 and L2. The split - a center tapped transformer - is how you get the 120 VAC into your house. Your common household outlets are 120 VAC (typical of US power systems, other countries have differing configurations). The power in your room is likely all connected to a single circuit breaker, meaning it's all on the same circuit as Max was pointing out. Simply using a different outlet doesn't mean being on a different circuit. You'd have to run an extension from another room. Even then your chances of finding a different circuit (L1 or L2) is a 50/50 mix. You may have to try several different outlets before you find one on a different circuit.

Back to the noise issues: Household power is fraught with noises of things switching on and off. Air conditioners, washing machines, fans, lights, other electronics - the list can get long. Each time something switches on there's a pull on the line. That pull is like plucking the string on a guitar. It's noise is short lived, but it's there. A good power supply is one that can handle those plucks and the end user doesn't notice anything different in their video or audio systems. Cheaper designed power supplies may not filter out that noise as well as the more expensive ones. That's probably why you see and hear issues on some equipment and not on others. As for the fan, inductive loads are typically noisy at all times. Not just at turn-on. Understanding how and why an inductive load can be noisy is complicated. But if you want to gain a simple understanding of how an inductive load can be noisy - take a small transformer. Take a small battery. With each hand, touch one lead of the battery to one lead of the transformer. Wait a second then pull the wire away from the transformer. You'll get a small shock. That shock is caused by the breakdown of the magnetic field you generated by connecting the battery. The same thing is happening (sort of) in an inductive load such as a fan. That snap you felt is what's (sort of) going on with the power lines in your home. That's the noise that can affect your monitor.

If you have one - try hooking your monitors to an Uninterruptible Power Supply (UPS). Don't plug the fan into it, just the monitors and speakers. My guess is that the noise will be gone. I can't guarantee that because none of us can do a complete diagnostics on your home electrical system or how well your equipment is designed. And yes, the full understanding of these issues IS a complicated subject. I've given you the best I can under the circumstances. Hopefully it helps you get a rudimentary idea of how and why your fan is messing with some of your electronics but not all of them.

#### Blibo_baggins

Joined Sep 2, 2019
6
Online or line interactive UPS? Online costs £4,000 onwards. Can't afford that obviously. The £400-£600 ones usually don't even state if they are line interactive or not even by leading companies like APC.

I will be plugging my PC into the UPS too.

No one is talking about whether these things like what the fan causes, will damage my components over time or not.

Joined Jul 18, 2013
23,619
No one is talking about whether these things like what the fan causes, will damage my components over time or not.
Sounds like you are looking for a definitive answer!
I don't think anyone here with come out and state categorically what exactly is going on, from a distance and without actually making some qualified tests.!
Max.

#### Tonyr1084

Joined Sep 24, 2015
6,264
 Oops. Posted the wrong answer to this question. Error removed.

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#### ElectricSpidey

Joined Dec 2, 2017
1,801
You probably don't need a UPS, a simple line conditioner would probably do the job, as long as the problem isn't RFI.

And yes, there is a possibility of doing damage to your equipment, but it is remote.