bsoltan

Questions (which-do-not-deserve-their-own-thread) Thread

3,027 posts in this topic

On 6/14/2017 at 11:03 PM, gavpowell said:

Probably only for Shogun, this one, but we have some very knowledgeable members here so maybe not:

Can someone explain to me the concept of electrically noisy appliances? They've been blamed for broadband issues in the past and homeplugs all cite noisy electricals as a limiting factor.

I don't understand this - we have wiring standards and electrical safety standards, and surely most appliances follow a pretty standard design?

So you get a kettle and it's 12V and however many watts. You plug it in and it takes electric from the supply, but it's surely not feeding anything back into the mains circuit? So how does it cause interference? 

Wiring and safety standards do not have anything to do with interference. For that we're into the dark world of EMC.

This is a very black art of which I am not well versed, however...


Remember back to school and the connection between electricity and magnetism?

Everything which takes power (as current flow) will generate a proportionate magnetic field...and every magnetic field will induce a current into it's neighbor.

So, basically, everything makes electrical noise and everything is affected by electrical noise.

A PC PSU is a good example. A SWITCH MODE PSU takes massive current pulses which, if you could hear it, would be like a machine gun firing.

Those current pulses will rattle the mains which will affect the HomePlugs.

[As an aside, I recall reading something in an EMC magazine a few years back where they were struggling to get Homeplug-type devices through approvals because of the amount of EMC noise they were making!]

Only by careful design can the noise be reduced...and it will only be reduced enough to "pass the test". And the level of noise will only be tested on and R&D sample - I doubt every product manufactured would be subject to a full EMC test! It will be declared "right by design".

 

Companies go to a lot of time and effort (and money!) getting their products to pass EMC tests, of which there's two areas.

1) Susceptibility - how much $hit your stuff can with-stand before it falls over.

2) Emissions - how much $hit your stuff puts out while going about it's business.

 

The ideal situation is for (2) to be less than (1) in all cases!

Sorry for any errors!

 

BR
JN

 

 

 

gavpowell likes this

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