VFD created static

morepower

Member
I have a client that only listens to AM talk radio. A VFD has been added to his well pump and is driving the radio crazy with static. Does anyone have a recommendation as to how to shield the vfd or the radio?
 
The VFD may not be well-shielded.
The leads to the motor may not be (well) shielded.
The VFD may have FCC Class-A RF emissions, not B ("Class A emissions refer to equipment that is used in any industrial environment, whereas Class B refers to equipment that is used in the residential sector. ")

Shielding the radio tends to cut off all reception :D.
 

Dzboyce

Senior Member
Location
Royal City, WA
Occupation
Washington 03 Electrician & plumber
I have a client that only listens to AM talk radio. A VFD has been added to his well pump and is driving the radio crazy with static. Does anyone have a recommendation as to how to shield the vfd or the radio?
I assume it's either a Franklin subdrive or Pentair Intellidrive. Both brands have RFI filters available to add on. I've only experienced this problem once on a 5 hp sub pump running on an Intellidrive PID50. You would get static on the AM radio if you were within 30-50 feet of the pump house. This system was for H2A farm worker housing and the closest building was over 100 feet away from the pump house. So nothing was done about the RFI.
 

paulengr

Senior Member
I assume it's either a Franklin subdrive or Pentair Intellidrive. Both brands have RFI filters available to add on. I've only experienced this problem once on a 5 hp sub pump running on an Intellidrive PID50. You would get static on the AM radio if you were within 30-50 feet of the pump house. This system was for H2A farm worker housing and the closest building was over 100 feet away from the pump house. So nothing was done about the RFI.
Buzz. Try again. Those filters are megahertz range to satisfy stupid Euro requirements.
 

paulengr

Senior Member
VFDs must have stranded wiring and must have a ground between it and the motor frame. This is not optional. It is very desirable to run wiring in metallic enclosures and conduit, again properly bonded and grounded. Also some VFDs come with or have optional RFI or EMC filters but those are to meet mandatory European regulations and don’t significantly affect anything under a few megahertz. The AM radio band is centered at 1 MHz with a 455 KHz intermediate frequency.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
VFDs must have stranded wiring and must have a ground between it and the motor frame. This is not optional. It is very desirable to run wiring in metallic enclosures and conduit, again properly bonded and grounded.
I want to amplify that the ground between the VFD and the motor frame is _critical_.

The way VFDs work, the entire motor winding gets 'switched' between the positive and negative DC rail at the PWM switching frequency. This creates _huge_ ground current spikes through capacitive coupling of the motor winding to the motor frame. These current spikes need to return to the VFD, and if the path taken to the VFD doesn't closely follow the path of the power conductors, then these high frequency currents will radiate.

-Jon
 

myspark

Senior Member
Location
SCV Ca, USA
Occupation
Retired EE
I have a client that only listens to AM talk radio. A VFD has been added to his well pump and is driving the radio crazy with static.

Does anyone have a recommendation as to how to shield the vfd or the radio?
Before spending valuable time and money in suppressing EMI or RFI—try the simplistic and inexpensive approach.
EMI or RFI can be caused by about almost anything that we have at home.. . . even the SUN can cause this anomaly. Switched mode power supplies, electric blankets, switching loads at home, doorbell transformers , your toaster , Bluetooth units etc.

Since AM operates well below the 805.11b (FM operates higher) protocol. . . you may not be affected by its higher frequency range.

The most effective RFI suppression solution is using a SNUBBER Circuit. This type is often used by connecting a series resistor across a contact. But since you already know what’s causing it (the VFD) consider yourself lucky-- so you won’t have to do any Trial and Error trouble shooting.
The most inexpensive solution is using a FERRITE BEADS that you install at the power input to the VFD.

That’s that doughnut-like contraption that you see.. . available on line. . . cost almost dime a dozen. lol.

Good luck and keep us abreast on your troubleshooting.
 

paulengr

Senior Member
Before spending valuable time and money in suppressing EMI or RFI—try the simplistic and inexpensive approach.
EMI or RFI can be caused by about almost anything that we have at home.. . . even the SUN can cause this anomaly. Switched mode power supplies, electric blankets, switching loads at home, doorbell transformers , your toaster , Bluetooth units etc.

Since AM operates well below the 805.11b (FM operates higher) protocol. . . you may not be affected by its higher frequency range.

The most effective RFI suppression solution is using a SNUBBER Circuit. This type is often used by connecting a series resistor across a contact. But since you already know what’s causing it (the VFD) consider yourself lucky-- so you won’t have to do any Trial and Error trouble shooting.
The most inexpensive solution is using a FERRITE BEADS that you install at the power input to the VFD.

That’s that doughnut-like contraption that you see.. . available on line. . . cost almost dime a dozen. lol.

Good luck and keep us abreast on your troubleshooting.
VFDs generate large current harmonics. Unless your voltage source is very close to overloaded this doesn’t matter. Current harmonics pull current through a big impedance and cause voltage harmonics, get it? Your ferrite beads are nonlinear EMI devices that block megahertz range voltage harmonics. They do nothing on the load (motor) side which if improperly installed radiated RFI not EMI everywhere. I’ve even had problems with 4-20 mA current loops because of this. That’s saying something! It takes a lot to mess those up.

So...try again. Make sure radio is well grounded too.
 

myspark

Senior Member
Location
SCV Ca, USA
Occupation
Retired EE
I'm not in here to argue with what you have in mind. OP needs some ideas (read his post).
I've worked with the early VFDs (formerly called PWM) pulse wave modulation-- more than than thirty years ago.
We'll see what OP has to say.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
For VFDs the ferrite beads can get quite large and expensive.

The ferrite will have a common mode choking effect; you don't want to choke the capacitive return current, so in this case the ferrite should enclose the circuit conductors and the ground from motor to VFD.

Jon
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
I have a client that only listens to AM talk radio. A VFD has been added to his well pump and is driving the radio crazy with static. Does anyone have a recommendation as to how to shield the vfd or the radio?
AM (amplitude modulation) is a "linear" modulation which means that the relative level between the desired audio signal and the noise/static (i.e., the signal to noise or S/N) is directly proportional to level of RF signal to noise (aka carrier to noise C/N). In other words, to get a 20 dB improvement in audio signal to noise (S/N) you need the RF noise from the VFD at the radio to be reduced by 20 dB. But "driving the radio crazy with static" means that the RF carrier to noise is quite low (lots of RF noise), and so the RF noise will have to be reduced a substantial amount to make the noise not be noticeable. That might be difficult unless there's "low hanging fruit" that provides easy opportunities for improvement (like no ground return from the VFD to the motor which Jon has brought up, no shielding on the conductors, etc.). Filtering of course can help, but there may be more than one path that is conducting and radiating the interference.

I'm just bringing this up because it might not be easy to fix this to the customer's satisfaction, depending on what's there now.
That's why I suggested in post #4 that streaming audio from an internet connection could be used if available.

By the way FM broadcast radio is much more immune to interference because of its "capture " effect, plus the fact that its RF channel frequencies are about 100 times higher than AM broadcast signals and so the level of RF interference from the VFD's IGBT switching waveforms will be noticeably reduced.
 
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