[Top] [All Lists]

Re: [RFI] Variable speed drives

To: "RFI List" <rfi@contesting.com>
Subject: Re: [RFI] Variable speed drives
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Tue, 27 Mar 2007 08:35:39 -0700
List-post: <mailto:rfi@contesting.com>
On Tue, 27 Mar 2007 09:36:38 -0500, dgsvetan@rockwellcollins.com 

>As the LG design seems to show, the "hash" can be reduced to 
>acceptable levels if the correct engineering and production 
>techniques and materials are used. 

Yes. We occasionally run into big problems with VFD's in pro audio 
installations, where they are used for elevators, HVAC systems, and 
geothermal systems. Like most other RFI issues, There, the problem 
occurs when the designer or installer sets up a large loop area for 
the RF components of the motor current by putting the power source 
(stepdown transformer and controller) in one place and the motor in 
another.  Stray and bypass capacitance to ground in the motor carries 
current in the large loop back to the ground of the transformer 
and/or the controller, so you've got a big and nasty magnetic field 
at LF, becoming EM at MF and HF. 

As any good EMC engineer knows, RFI problems can be minimized by such 
time honored techniques as minimizing loop areas, controlling rise 
times, and suitable shielding. 

Thanks to all who have named names. It makes it easier for us to be 
educated consumers. 


Jim Brown K9YC

RFI mailing list

<Prev in Thread] Current Thread [Next in Thread>