[Top] [All Lists]

Re: [RFI] Replacing EMI components in a computer power supply

To: "RFI List" <rfi@contesting.com>
Subject: Re: [RFI] Replacing EMI components in a computer power supply
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Mon, 22 Mar 2010 11:37:48 -0700
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On Mon, 22 Mar 2010 10:39:53 -0400, Pete Smith wrote:

>The supply appears to have places for two toroidal inductors and a shunt 
>capacitor on the input side.  Would it make sense to try to find and 
>install these pieces, or am I better off just buying and installing a 
>power entry module such as the Qualtek Q468-ND in this noisy bugger.  
>Its peak RF output is right around 2 MHz.

The first thing I would try is fourteen turns of the power cord around a #
31 2.4-inch toroid. If that makes a dent but you need more, rewind it with 
two toroids in a stack. For the shunt capacitor, fire safety dictates that 
you MUST use one that is rated for the high peak voltages that can be 
present on the power line. Here's what I wrote for the ARRL Handbook on 
that topic. You can find suitable capacitors from the usual industrial 
suspects -- Allied, Newark, Mouser, Digikey. 

=   =   =   =   =   =  =

A capacitor between line and neutral or between line and ground at the 
noise source or at victim equipment can solve some RFI problems. ["Ground" 
in this sense is not "earth,' it is the power system equipment ground (the 
green wire) at the equipment.] Power lines are often subjected to short 
spikes of very high voltage (4kV). Ordinary capacitors are likely to fail 
when subjected to these voltages, and the failure could cause a fire.  Only 
Type X1, X2, Y1 and Y2 capacitors, which are specifically tested to 
withstand these high voltage spikes, should be used on power wiring.  Type 
X1 and X2 capacitors are rated for use between line and neutral, and are 
available in values between 0.1 æF and 1 æF. Type X2 capacitors are tested 
to withstand 2.5kV, type X1 capacitors are tested to 4kV.  Type Y1 and Y2 
capacitors are rated for use between line and ground; Y1 capacitors are 
impulse tested to 8kV; Type Y2 to 5kV. Note that 4700 pF is the largest 
value permitted to be used between line and ground  larger values can 
result in excessive leakage currents.

=   =   =   =   =   =


Jim K9YC

RFI mailing list
<Prev in Thread] Current Thread [Next in Thread>