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Posted by Glenn on May 03, 2026 at 02:39:42.
In Reply to: Re: To Gedas about filtering noise from the LW Band posted by Gedas W8BYA on May 02, 2026 at 20:00:51.
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I have been learning from a Phd that teaches and designs these for several companies. He completely contradicts the design of the one I bought with the 10 Khz rating. He teaches putting a differential mode cap (safety cap, X type) across the incoming line followed by a common mode choke of 2.5 to 10 mHs (depending on how steep you want to go) followed by two Y safety caps that Y together to ground and then two normal mode chokes of .48 mHs (in neutral and hot) then followed by another X cap across neutral and hot for differential mode. The X cap is decided by efficiency (how much parasitic reactance you can tolerate that would draw more current). According to him the Y caps are sized for a return current to ground of no more than 3 ma. It's actually less but the point is that a person could be exposed to the current and I understand this to be regulatory. It sounds much like you are saying. The values I stated were from an example he gave for areas down to 40 Khz. But in seeing all that I have seen lately there was a lot of commonality with what he was saying and what others say. I was trying to simulate these on LTSpice but I found out there is a lot going on in the creation of a common mode choke that throws off your simulation. As soon as I work that out I will start putting some of these together. I used to buy AC and DC line filters for control systems but never thought about the lower frequencies being a problem. Boy I was wrong! I didn't have VFD problems at the time because we only had one or two in each location. And we certainly had no switching power supplies (except UPS's in a motor control center). At that time too I did not think so much in terms of what really constitutes these problems. Well, I was fortunate but glad to have them spec'ed out. When I studied industrial electronics we looked at every kind of filter under the sun but no AC line filters. People didn't use many.
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