Reply To: Motor query for 3 phase VFD conversion

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

On SillyOldDuffer Said:

On john fletcher 1 Said:

Regarding VFD and possible interference, has any one fitted an ex washing filter block, capacitors and chokes, there are plenty around and what was the result ?

….

I predict the result won’t be perfect, but it should reduce the problem.  Whether or not it’s worth the effort is unknown!  …  I don’t believe there are any H&S concerns provided the usual electrical guidance is followed.

Dave

There are significant safety issues with mains filters. Don’t DIY them unless you know what you are doing. If it was easy electronic equipment manufacturers would make their own rather than buying them from Schaffner et al. Even using parts from an existing filter can be dangerous. …
If you have to ask how, don’t even think about doing it.

Robert.

Can you explain in more detail please Robert?  John, who if I remember correctly is a retired electrician, is asking about fitting a sealed manufactured EMC filter from a washing machine in front of his VFD.   How is that dangerous, especially if he does the work?

In terms of performance, not safety, my feeling is a washing machine filter won’t be brilliant at suppressing the muck coming out of a VFD.  That’s why I suggested it might be improved by adding capacitors.  I plead guilty to assuming readers know the capacitors have to be mains rated components, not standard fare.  I also failed to explain what values might be suitable, or how to test whether or not the filter is improved by them.

Though John may not know anything about filter design, I’m confident he could wire one up without coming to grief.  And important to note, no-one is expecting a washing machine filter to be as well engineered as one designed to meet an EMC specification.   It only has to reduce the problem by a useful amount – a mere 50% reduction would be helpful.

Any job can be tackled provided risk is managed.  In this example I’m not aware of anything about fitting a washing machine EMC filter that’s high risk or high impact if it goes wrong.   As always I might have missed something though!  What’s the worst that could happen?

Ta,

Dave