Why do phone chargers cause radio interference?

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Vrbic
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TL;DR Summary
What is the physical reason for the interference of radio by phone charger?
Hello everyone,
I'm not sure I write in the right part of the forum. If not please point me somewhere.
Query:
I noticed some of the phone chargers interferes with digital radio. I checked some forums and I found reasons like that: It is a low-quality charger and it generates a huge amount of a high-frequency of the noise.
- Ok, but what means the noise?
I suppose electromagnetic noise. Right?
If yes, it means some charge has to oscillate or electric field. I don't see anything like that in a phone charger (if I don't count the oscillation of alternating current in the outlet).

Especially, I hear a periodical disturbing of the radio signal, ie. radio works ok few seconds and then it stops work for a second or two and then it is again ok for a few seconds.
This behaviour seems to me like:
1) Something is charging and then it relaxes and emits some electromagnetic waves.
Or
2) It emits still, but the frequency is periodically changing and when the frequency is the same as the radio signal it interferes the radio.

Any why still here is my main question: What causes an emission of electromagnetic waves?

If anyone can describe what happening there I'm very curious.
Thank you.
 

Answers and Replies

  • #2
tech99
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The charger uses a switch mode power supply, where current is rapidly turned on and off. This switching waveform has a lot of energy at the frequency of its harmonics, which are at radio frequencies, and some of these fall within the spectrum used for broadcasting. The energy is mainly radiated by the wiring. The radiated energy can be reduced by good design.
And if you find it annoying, wait until cordless electric vehicle chargers become commonplace.
 
  • #3
Vrbic
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The charger uses a switch mode power supply, where current is rapidly turned on and off. This switching waveform has a lot of energy at the frequency of its harmonics, which are at radio frequencies, and some of these fall within the spectrum used for broadcasting. The energy is mainly radiated by the wiring. The radiated energy can be reduced by good design.
Thank you very much for your answer!

And if you find it annoying, wait until cordless electric vehicle chargers become commonplace.
Are you touching a spreading of electric cars and their charging? Why?
 
  • #4
tech99
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Thank you very much for your answer!


Are you touching a spreading of electric cars and their charging? Why?
The charging of electric vehiocles, if carried out cordlessly, will require many kilowatts of radio frequency power to be applied to something like a coil of wire in the ground. It will likely be impossible to reduce the harmonics sufficiently to prevent serious radio interference.
 
  • #5
Vrbic
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The charging of electric vehiocles, if carried out cordlessly, will require many kilowatts of radio frequency power to be applied to something like a coil of wire in the ground. It will likely be impossible to reduce the harmonics sufficiently to prevent serious radio interference.
Understand!

Now I'm checking the "switched-mode power supply" here https://en.wikipedia.org/wiki/Switched-mode_power_supply and I'm looking which process causes interfering electromagnetic emission. Do you know what is it?
 
  • #6
anorlunda
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The charging of electric vehiocles, if carried out cordlessly, will require many kilowatts of radio frequency power to be applied to something like a coil of wire in the ground. It will likely be impossible to reduce the harmonics sufficiently to prevent serious radio interference.
That's a new one on me. I never thought about it because I always assumed that the energy losses and heating would make it unattractive.


But I agree that if we did have cordless EV charging, that the EMI would be a big problem. Would the FCC EMI requirements apply to that?
 
  • #7
davenn
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and I'm looking which process causes interfering electromagnetic emission. Do you know what is it?

mostly from the high voltage switching side and assoc. windings of the transformer
as I have circled...


SMPS1.JPG
 
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  • #8
tech99
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I believe the cordless charging of electric vehicles is seen as th future, both at homes and for buses when they stop at traffic lights etc. Typically we are talking 7.5kW at maybe 50 kHz. To reduce emissions to an acceptable level is very difficult. For instance, 1 microwatt interfering power requires an attenuation of about 100dB.
 
  • #9
nsaspook
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I believe the cordless charging of electric vehicles is seen as th future, both at homes and for buses when they stop at traffic lights etc.
...

I hope not. Wireless energy transfer is wasteful (because of basic physics) when not optimized by proper mechanical alignment and close proximity. At low cellphone power levels, needing 20W to deliver 10W is acceptable. 15kW for 7.5kW results in a huge increase of needed generation with wide usage.

https://spectrum.ieee.org/transportation/mass-transit/a-critical-look-at-wireless-power
https://www.wirelesspowerconsortium...chnology/effficiency/transfer-efficiency.html
 
  • #10
Vrbic
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I believe the cordless charging of electric vehicles is seen as th future, both at homes and for buses when they stop at traffic lights etc. Typically we are talking 7.5kW at maybe 50 kHz. To reduce emissions to an acceptable level is very difficult. For instance, 1 microwatt interfering power requires an attenuation of about 100dB.
How about laser/maser charging? I mean by a relatively narrow beam?
 
  • #11
Vrbic
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mostly from the high voltage switching side and assoc. windings of the transformer
as I have circled...


View attachment 276537
Ok, thank you!
Why isn't it constant interference? Why is it periodical?
 
  • #12
tech99
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I imagine the charger is intelligent and is cycling the charge on and off.
 
  • #13
davenn
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Ok, thank you!
Why isn't it constant interference? Why is it periodical?

I imagine the charger is intelligent and is cycling the charge on and off.


would have been my first thought as well :smile:
 
  • #14
tech99
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How about laser/maser charging? I mean by a relatively narrow beam?
Maybe there are safety issues. I suppose an induction loop at low frequency will not couple energy into the human body whereas infra red and microwaves will.
 
  • #15
nsaspook
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