[RFI] Help on speed drive motor controller RFI

Tom Rauch w8ji at contesting.com
Sun Jan 28 22:13:14 EST 2007

> Ask to see the documents for the declaration of "CE" 
> conformance, which
> apply to every country in the European Union.
> On the face of it, it seems impossible that such a system 
> could meet the
> regulations for conducted emissions of 15kHz and its 
> harmonics without
> using RFI filtering.

Having had first hand experience with this exact problem, 
put me on the record as disagreeing. A controller can easily 
pass conducted emissions in CE or FCC testing by a wide 
margin and be horrible near an amateur or commercial HF 
receiving system.

I've cleaned up speed controllers (three phase from a German 
company) and filter and suppression help from the 
manufacturer is useless. They don't understand radiated 
noise, and the filters they sell have excellent suppression 
below the HF bands but don't do much at all at HF. The fact 
it is FCC approved or CE approved doesn't mean a thing when 
the controller is near radio gear, especially if it is used 
in or near an HF system.

I've made systems I've worked on so noise-free you can hold 
a receiver next to the case and not hear the controller, but 
I had to design custom filters in RF tight boxes for the 
motor leads, control, and power leads. The entire controller 
had to be enclosed in a properly designed box with copper 
screening over the vents and everything entering and leaving 
through multi-section shielded filters. The filters also had 
to withstand the high transient voltages and high starting 
currents of the inductive load while not causing the peak 
current to be out of spec for the controller. It was 
designed to look into an inductive load and there were 
cautions about using it into a capacitive load beyond a 
certain capacitance.

The power line is not the issue, the line to the load is.

73 Tom

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