Does an EMC/EMI filter like https://www.valinonline.com/products/508-120 go before the VFD or after the VFD on the cable that goes to the spindle? Also, if I use a filter on the output side of the VFD, would this protect both the VFD and the motor?
EMC/EMI filter question
- Thread starter lbarber70
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Filter should be BEFORE the VFD.
Any suppression components should go BEFORE the circuit—be it for the purpose of amplification, conversion or inversion.
Any irregular or undesired oscillation of frequency must be reduced or eliminated before a signal is processed, enhanced or amplified.
If you have worked on audio or video systems for example-- you will notice all kinds of distortions, noises, fade-outs-- or in the case of videos-- pixellations and blue screens.
Any undesired oscillation or frequency (spikes) must be handled prior to finalizing the refined signal.
If the output is directed to a voice coil of a speaker for example, this output must be clean as possible or you will hear gurgle, hisses and squeals.
Putting this EMI filter AFTER the amplifier-- will not correct the problem. In the case of the motor connected to the VFD controller—this irregularity will not protect the motor after the power had gone through the control board.
This analogy of the amplifier is no different from having a VFD controller where components could be subjected to noises, spikes and other transients.
As an aside: you notice those ferrite cores that come with Laptops and printers. . . they are clamped on to the end of the cord before is goes to the power port. It suppresses those generated radio energy from being broadcast to nearby electronics and the electronics system being served.
This is the cheapest type RFI/EMIs.
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Note that for long lines from VFD to motor or with a non-inverter-rated motor you may be motivated to use a pure sine filter. That would go between the VFD and the motor, and would be a very different animal from an RFI/EMI/EMC filter which is intended to reduce unwanted high frequency components from affecting other equipment.
However, if the lines from the VFD to the motor are not shielded (either VFD cable or in metallic raceway) and are therefore able to radiate noise, you may also need to use a filter on the output side of the VFD.
However, if the lines from the VFD to the motor are not shielded (either VFD cable or in metallic raceway) and are therefore able to radiate noise, you may also need to use a filter on the output side of the VFD.
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Or just shield them... it's a LOT less expensive!
VFD output = Pulse Width Modulation and Variable Frequency. That is VERY close to being "Frequency Modulation", a.k.a. FM radio transmission! The wires from the VFD to the motor are somewhat powerful radio broadcast antennae if not shielded.
Decades ago I built a control system for a concrete deposition machine that was dumping concrete in spiral rings into holes for underground nuke tests. I was still young and dumb and full of you-know-what at the time and since virtually everything in this machine was in constant motion, they wired everything up with SO cord, including the conveyor motors that were on VFDs. During site testing in the Nevada desert, we were descended upon by Army scientists and MPs with guns drawn because they didn't know we were out there and why. Turned out they had triangulated on us from 25+ miles away using the RF signals coming from the unshielded SO cords on the VFD outputs... Now mind you, their instruments were probably a lot more sensitive than average based on what they do, but it was an eye opener as to just how much RF is coming out of a VFD.
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