3 phase - radio puzzle

The Warco 918 lathe I have recently bought is 3 phase with a IMO Jaguar Cub VFD and all is well. However the wife pointed out yesterday that when I run the lathe her kitchen radio (battery operated) stops working. I checked it out and she is correct and yet the workshop radio again battery powered and only 5 feet from the lathe has no problems.

Any ideas guys..?

For a non-technical solution you could try swapping the radios over. You probably can't hear the workshop one with the lathe running anyway. Sounds like the filter in the VFD might be faulty.

John

I fitted a separate filter to VDF 3 phase mill power supply

Just checked again and the kitchen radio doesnt actually cut off but it makes an awful noise.

John, changed the radios over and still the same, the kitchen radio location is the problem, the workshop one is fine.

+1 on the EMC filter. I fitted one when I did my lathe conversion and have never had any issues.
Only thing to watch out for is additional earth leakage, which may trip your RCD.

Thanks guys, so it sounds like a filter problem, but why the kitchen radio which is 30 feet away and not the workshop one which is only 5 feet from the lathe, dont understand that..?

Is the kitchen radio in close proximity to house wiring, could be that the interference from the inverter is causing a field effect around the house wiring, try moving the radio away from any wiring and see if that makes any difference. My IPhone chargers can cause interference if the wire runs close to a radio, I have an alarm clock/radio on my bedside cabinet and I charge my IPhone on there as well, have to make sure that the charger cable is not near the radio otherwise it causes interference.

Dave W

Are you tuning to the same station in each location?

Yes local bbc radio Devon on all of them, tried two bedroom radios and they are fine.

Is this Radio Devon on medium wave or fm showing the problem?

No one has mentioned or asked the frequencies or bands in use by these radios. Medium wave, VHF/FM, DAB? If they are set to different bands, it is quite likely that one will be interfered with but not the other, even if listening to the same station, Radio Devon in this case.

A problem on both MW and FM

Depending on your location relative to the fm transmitter your reception could be very variable even at different points around your property (multipath reception). Devon wasn't designed for good fm reception, the terrain is too lumpy (same problem just up the road in W Somerset!). As for MW, I don't have the info to hand but the MW transmitter is probably relatively flea-powered.

Your installation looks good, IMO is a good pedigree piece of kit, I'm not inclined to think there's anything wrong. All VFDs will produce interference, reduced but not eliminated by built in filters. It's quite likely your kit is all 'in spec' but your BBC signals are weak at your location.

Try a different station perhaps.

Some VFDs have built in RFI filters, but these are typically only rated for 'industrial use' (where there might be more tolerance of some noise on the mains). Some of these filters can be switched out of circuit !

If you fit an input filter, it should be on the metal backplane that the VFD is mounted to for best performance (I've seen them located using Velcro strips !).

Earth connections and screen connections (not the same thing) are important. Screen on power connections should be bonded directly to the metal backplane.

Metal cabinet door should be bonded to cabinet body/backplane.

There is lots of good information on line - also lots of people contradicting that good advice. The installation manual for the specific VFD can often be a very good source of advice.

Radio Devon is on six VHF channels in the area, two MW freq's, DAB Multiplex 10C (Between 174-240 MHz) Freeview Ch. 720, and iPlayer. Mix and match these for best reception on each radio.

First thing might be to check whether it is only while the motor is running or while the VFD is switched on. The RFI is likely emitted from the motor feed cable. Is this screened cable? Length of the cable can also be an important factor.

Needs sorting if you have neighbours who don’t yet know why their radio reception is a bit ‘iffy’ on occasions.

Only when the motor is running, motor cable 1.5 mtrs and would need to remove a cover to check if its screened

Could just as easily be conducted RFI back into the mains - in fact that is more likely given Ron's previous comments.

It is likely differential mode conducted interference from the VFD causing the issue. You should fit a suitable filter on the inlet. Most VFD instructions say one is required.
The current from differential interference flows in opposite directions on the two conductors.(Live and neutral). Where these are close together and physically balanced the fields cancel and no signal is radiated. This is likely the case near the VFD hence no interference near it. The house wiring on the other hand is less likely to be balanced especially lighting wiring. Un-balanced or separated conductors act as an antenna so when the currents reach the house wiring they radiate and cause interference.

All VFDs should be in a swarf and splash proof (at least IP34, preferably IP 45 or better) earthed metal box with appropriate mains switching, fuse, filter, ventilation or space for cooling and cable glands or connectors.

Robert G8RPI.

I managed to get hold of a secondhand double 13 anp socket with built in RFI filter. The VFD is always fed through that. No problems with either Radio or TV.

The baby alarm installed to hear the front door bell makes a hissing noise, although the bell, or even unlocking the front door is easily audible. Almost like an electronic version of tinnitus!

My 2p is to install a RFI in the feed to the VFD.

Howard