RF interference from variable speed pump

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Special

Member
Aug 12, 2019
8
Southwest Ohio
I have interference on the (don't laugh) AM band on my radio when running my Variable Speed Pump and wondered if anyone else has had this problem and fixed it.
The radio is over 50 feet from the pump and the pump is grounded internally and externally.
 
Welcome to TFP!

I'm an amateur radio operator, so I don't laugh at RFI at any frequency. Is it a broadband across the whole band, or on a specific frequency/frequencies? Is your radio plugged in to the wall or on batteries? If plugged in, can you use batteries to see if the problem persists? If you don't have a battery powered radio can you try listening from your car?

This will help narrow down where the interference is coming in to the radio and perhaps give us a simple solution.
 
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Special said:
I have interference on the (don't laugh) AM band on my radio when running my Variable Speed Pump and wondered if anyone else has had this problem and fixed it.
The radio is over 50 feet from the pump and the pump is grounded internally and externally.
Click to expand...

Problem is that AM radios today are garbage. Easy answer is to get the radio as far from the pump as possible. Other option is a C. Crane radio.
 
Don''t know if it is broad spectrum yet, I will look into it more tomorrow. The pump is at least 50ft away, down a level and through several walls from the receiver in my garage. I didn't notice it a couple days ago when I was working in the garage but sure noticed it today, I'm worried it may affect my wireless network too.
I'll report back tomorrow what I find.
 
AM radio is 550 KHz to 1.7 MHz. Wifi is 2400 and 5760 MHz. Impulse noise won't usually even interfere with VHF at a hundred MHz. So you won't have issues with your wifi. However as an amateur operator and a (former) RF engineer I would be concerned with the AM interference. It might be possible to put a EMI/RFI filter on the pump, but it also might mean something is actually wrong with the pump. What model of pump is it?
 
Amateur radio operator here also.

Does the sound of the AM static interference change when you vary the speed of the pump?

Take your portable AM radio and move it around the pump and electrical wiring. Does the volume of the static change in volume as you move it around? If so find the location where it is the loudest.

What is the sound of the interference? Crackling static or a whine?

Anyone remember when the ignition systems of cars would interfere with its AM radio? Bad ignition lead or worn generator brushes would drown out weak AM radio stations. Sparking creates static on AM frequencies which is concerning for a modern motor. Modern electronics should not be generating AM interference.
 
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Ok here's what I found, I took portable radio out and bumped the control box and the static stopped.
Just a little history on the motor, I purchased this pump as open box very cheaply because it had been dropped and broke 2 of the standoff's on the motor that the control panel mounts to, I'm guessing the control panel bolt is not making good contact with the mounting bolt. Since tightening the bolt it has stopped but I'm sure it will return at some point. Is there something I can put on the bolt to help with making a good connection?

ajw22 said:
Anyone remember when the ignition systems of cars would interfere with its AM radio? Bad ignition lead or worn generator brushes would drown out weak AM radio stations. Sparking creates static on AM frequencies which is concerning for a modern motor. Modern electronics should not be generating AM interference.
Click to expand...
I do and I still have several cars that do it on a portable bluetooth speaker. The cars are 90 years old and do not have radios in them so sometimes we will bring a speaker along to have music.
 
I am not sure it is a problem of the bolt not making a good connection. Could have been a loose plug or wire that is now back in place.

Or the control panel forms a shield keeping RF within its box. There was a gap where the RF was leaking out and you closed that gap when you tightened the bolt.

I would not worry about it until the next time you hear the static. Then you know where to look.
 

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VFDs create line noise and harmonics due to the way that they convert single phase power into 3 phase power at different frequencies. They don't create smooth sine waves. They create blocky simulated 3 phase sine waves. Here's a video that helps explain it.

 
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I don't think stainless will "gall" much in Aluminum.. (Though it is possible: "Mating parts of the same alloy have a greater tendency to gall than those of dissimilar alloys. However, not all combinations of stainless steel act the same. For instance, a 400 series stainless steel nut can work well on a 316 series bolt, but this will cause a reduction in the overall corrosion resistance of the assembly. ") However if you are worried, go to the hardware store and get some "silver never seez" and it won't gall no matter what. I would also agree with tightening up/wiggling connectors internally, etc. but I also agree that "next time" or "when you get around to it" is sufficient....
 
The VFD might not be making good contact with the power connection plug to the motor.

VFDs create stray currents and harmonics. This is what trips standard GFCIs and creates radiated radio frequencies.

To fully understand what's going on, you would need a radio frequency monitor and an oscilloscope on the in and out power for the VFD.
 
Where I work we have aluminum bodied apparatus and the stainless bolts they use to secure taillights and grab bars sometime will corrode, snap off and have to be drilled out. The bolt that is on there is the original bolt.
I thought about using never seize but didn't want to prevent electrical connection between the two. I'm not sure of the electrical properties of never seize whether it is an insulator or conductor.
 
I wouldn't rely on the bolt for an electrical connection anyway... maybe bonding.. but not much else... however.. There is silver, graphite and copper in Never Seize... again to quote....

"Graphite is an excellent conductor of electricity and high temperature solid lubricant (up to 900 degrees F). ... Corrosion of a threaded joint increases the electrical resistance. The use of anti-seize on these types of connections will ensure current is transmitted reliably by preventing corrosion"...

So lube it up, my friend....
 
The way that the drive mounts, the drive has to be all the way down to make good contact with the plug that sends the three phase power into the motor.

If it's not fully down, the contact will be weaker and could account for the static.
 

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