A simple and effective VFD EMI filter

Well as you noted, the thread is old. After I have put the filter I forgot all about it as it performs perfectly. As for the isolation trafo I think that a filter is cheaper, consumes (almost) no energy and needs less space in comparison to any transformer, not to mention the weight of the latter.
I did not test an isolation transformer as a filter and it will be interesting to hear any experience of others for the matter!
 
petcnc said:
Well as you noted, the thread is old. After I have put the filter I forgot all about it as it performs perfectly. As for the isolation trafo I think that a filter is cheaper, consumes (almost) no energy and needs less space in comparison to any transformer, not to mention the weight of the latter.
I did not test an isolation transformer as a filter and it will be interesting to hear any experience of others for the matter!
Click to expand...
Thanks for the quick reply. The drawbacks you mention are perfectly reasonable, and make the isolation transformer a very crude ''brute force'' solution compared to a dedicated, fit for purpose filter designed for the task at hand and no more, as far as mass, bulk, price etc. But on the upside transformers are very versatile, commonly available and ''plug and play'' and could be used to feed several pieces of equipment and many people might already have one laying around, or might be able to get one for a reasonable price. Just an option to keep in mind.

Now I don't even know how effective an isolation transformer would be in a problematic situation like you experienced, but I have a feeling it would be very good. It would be really cool to see a side by side comparison. For example if you ever have access to a suitable transformer and wouldn't mind plugging it in for a back to back comparison with your current solution I would be very interested to hear.

I have a cheap 2.2 kW VFD that I have briefly played with, but not in use on an actual machine. I did not experience any issues like this myself, but it was a very brief test run on the bench. Maybe it would cause similar problems, maybe not (I don't even know if it might have, something like the loss of internet could very well have been missed in such a brief test). But I do have access to isolating transformers and will report back any findings.
 
A transformer would probably prove not as effective as the ferrite suppressors. Transformers have internal capacitance that would
pass HF noise signals easily right thru back to the power line
 
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markba633csi said:
A transformer would probably prove not as effective as the ferrite suppressors. Transformers have internal capacitance that would
pass HF noise signals easily right thru back to the power line
Click to expand...
Thanks for that. This was my concern too, although I couldn't describe it as well as you have. I really want an oscilloscope now!
 
Iron core transformers don't have great magnetic properties at high frequencies either, compared to ferrites
 
Thanks a lot for the links koenbro
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markba633csi
When you say ''Iron core transformers don't have great magnetic properties at high frequencies either'' do you mean at power line frequency like 50/60 Hz or do you mean a 3 phase transformer used on the output of the VFD where frequency could be much higher? I'm curious about that quote in general if you don't mind clarifying it for me (a novice but very keen to learn as much as I can about the electrical things). I know transformers are designed for a specific frequency and and would not work with a variable frequency supply (just my understanding!)
 
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