EMI and RFI filtration protection

I recent bought one of these:

http://www.computermarket.com.au/images/PT9988.jpg
http://www.nasa.com.au/products_computerac_ao-pto888.html
http://www.ecomcomputers.com.au/prodDetail.php?ID=434793&catid=


I was after this particular feature:

"EMI and RFI filtration protection"


I realise that for around $20 (Strathfield) that I'm not getting a proper UPS
but all I wanted was something to stop our radio from clicking while the the
washing machine is running in the house.

But it doesn't even do that.

Do you reckon I got a faulty unit or does "EMI and RFI filtration protection"
not mean what I think it does?

Thanks guys

Jeff

 

[Ruprect]

Jeff jeff_nospam@afterglow.org.au wrote:

I recent bought one of these:

http://www.computermarket.com.au/images/PT9988.jpg

But it doesn't even do that.

That's because you bought a powerboard with a couple of cheap MOVs
inside. If you spend about $100 you will get a good quality RF filter
inside as well.

However... what makes you think the RFI is entering via the mains and
not via your antenna? You may be better off having MOVs fitted to the
noise source (the washing machines relay contacts).

 

[Phil Allison]

<Jeff

I was after this particular feature:

"EMI and RFI filtration protection"

I realise that for around $20 (Strathfield) that I'm not getting a proper
UPS
but all I wanted was something to stop our radio from clicking while the
the
washing machine is running in the house.

But it doesn't even do that.

Do you reckon I got a faulty unit or does "EMI and RFI filtration
protection"
not mean what I think it does?

** The phrase "EMI and RFI filtration protection" naturally refers to the
AC supply circuit where the device is physically connected. It refers
specifically to *conducted* RFI flowing in the wires.

Your mistake is assuming that interference from the washer is being
injected into radios etc is via **conduction** through the AC wiring. What
about simple radiation through the air ???

A sparking switch generates RF currents in the wires that supply it so
those wires act like an antenna radiating the energy as EM waves into the
surrounding area. The antenna loop or stick on your radio receives this RF
energy and so does *every bit of wire* in the vicinity.

" Every bit of wire" includes things like speaker leads, audio connecting
cables and antenna cables, at least on their outside shields. The RFI is
then potentially let in the door to each and every electronic item in the
area resulting in pictures flashings and audible clicks and bangs from your
speakers.

The *answer* is to suppress the arcing switch itself - ie inside the
washer - with RC snubber networks.

Try the AC filter on the offending washer's power lead - it may or may
not help.

If it does not then you need expert help with that washer.




................ Phil

 

[Franc Zabkar]

On Sun, 21 Nov 2004 12:22:32 +1100, Jeff jeff_nospam@afterglow.org.au
put finger to keyboard and composed:

I recent bought one of these:

http://www.computermarket.com.au/images/PT9988.jpg
http://www.nasa.com.au/products_computerac_ao-pto888.html
http://www.ecomcomputers.com.au/prodDetail.php?ID=434793&catid=


I was after this particular feature:

"EMI and RFI filtration protection"


I realise that for around $20 (Strathfield) that I'm not getting a proper UPS
but all I wanted was something to stop our radio from clicking while the the
washing machine is running in the house.

But it doesn't even do that.

Do you reckon I got a faulty unit or does "EMI and RFI filtration protection"
not mean what I think it does?

The EMI/RFI filter at best consists of a 1uF cap across the active and
neutral, and two 15nF (?) caps between each terminal and earth. The
surge and spike suppression is probably provided by three MOVs. If you
have the DSE 2002-2003 catalogue, check the pictures on page 140 for
an insight into the internals. AFAICT, even DSE's $100 Zap Catcher
wouldn't give you much in the way of filtering, but it may be better
than nothing.

This is a *real* filter from a 1980's hard disc drive:
http://members.optusnet.com.au/~fzabkar/filter.jpg

It is rated at 250VAC, 9A, 50/60Hz, and its dimensions are 100 x 135 x
45mm.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Ruprecht]

Franc Zabkar wrote:

The EMI/RFI filter at best consists of a 1uF cap across the active and
neutral, and two 15nF (?)

4n7 max (earth leakage rules).