[RFI] Impedance at 60 hz

Jim Brown jim at audiosystemsgroup.com
Fri May 22 12:00:22 EDT 2015

On Fri,5/22/2015 8:28 AM, Aaron Kreider wrote:
> How close is the impedance at 60 hz for material 31 to zero?


> I want to filter the inputs and outputs to my 5000 watt solar inverter 
> with ferrite chokes, and I'm wondering if there is any risk of 
> overheating?

The output of that inverter is not only 60 Hz -- if it produces RF 
noise, it's because it has strong square wave components.  If you add 
inductance in series with individual conductors, you will round off 
those square waves, which is likely to increase the dissipation in the 
switching devices, which could overheat them and cause them to fail. The 
same is true of charge regulators. Trying to filter these components can 
be like putting lipstick on a pig. Why not buy stuff that is RF clean in 
the first place?

We do not have an overheating problem if we wind all three conductors 
through a common mode choke, because the net current through the core is 
quite small (that is, the current in the phase conductor is cancelled by 
the current in the neutral). The problem with that is that conductors 
rated for 40A (I'm assuming 120VAC) can't be wound multiple turns 
through a ferrite core.  If it's 240VAC, you might manage an effective 
choke with #12 conductors, which are rated for 20A. For that choke, use 
both phases and green.

If you already own this beast, a better solution is a good line filter, 
properly installed. That means zero length leads, including a zero 
length bond between the shielding enclosure of the filter and the 
shielding enclosure of the inverter.

It's also a good move to run all pulsed currents in twisted pairs. This 
minimizes radiation from the differential component of the current.

73, Jim K9YC

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