Will VFD cause interferance on nearby CNC controler?

I've gone through about 8 pages of threads (about a 110 left to go) and tried search feature but not really finding what I'm looking for.

Senario: A CNC benchmill running on 220v single phase (not the problem).
A 3hp 3 phase manual lathe (considering a Hitachi WJ200 VFD per
recommendation of PM member) within 5 to 15' of one another
depending on where I decide to put lathe.

There's been a couple of blurbs about VFD's possibly causing interferance with a CNC's controller and scraping parts. Anyone know for sure if this is true and if so suggestions as what to do would be awesome.

I don't have the lathe or VFD yet so I still have options, just trying to do my homework but have absolutely no experience with electrical at all so I'm kinda lost as what to do.

Any advise would be greatly appreciated,

Thanks, James

interference = bad

Hi James,

VFDs DO have the potential to cause interference to other digital equipment.

The best insurance against such problems is to run the wires from the VFD to the motor in steel conduit. The VFD manual should tell you to do this.

It's also advisable to run all control wiring for the VFD (switches and speed controls) in a separate steel conduit, to protect them from external interference.

- Leigh

The real Leigh said:

Hi James,

VFDs DO have the potential to cause interference to other digital equipment.

The best insurance against such problems is to run the wires from the VFD to the motor in steel conduit. The VFD manual should tell you to do this.

It's also advisable to run all control wiring for the VFD (switches and speed controls) in a separate steel conduit, to protect them from external interference.

- Leigh

Click to expand...

Great I'll definately do that when the time comes...so I guess that means I don't have to use a RPC or even worse stay away from 3 phase all together.

Thanks for the info,
James

jvergopia said:

..........
Senario: A CNC benchmill running on 220v single phase (not the problem).
A 3hp 3 phase manual lathe (considering a Hitachi WJ200 VFD per
recommendation of PM member) within 5 to 15' of one another ..................Thanks, James

Click to expand...

James, as others have said, yes, VFDs generate lots of noise that can get into other equipment and cause problems. Using shielded motor cable or metal conduit on motor leads does reduce a large portion of the noise.

But to answer your specific question, copied above, no, you will not have any noise problems from the motor leads in this scenario as the noise from the motor leads radiates into other wires within about 12" of them causing the majority of the noise. Your 5+ feet distance between machines means this will not happen.

That said, there IS still potential of noise unrelated to this distance that may still get into your CNC altho it does not happen often: noise that comes out of the VFD and goes up the 220v power lines that feed the VFD. If that happens you would address it with a noise filter between your drive and the 220v source. Most installations do not require this so I would not suggest spending any money on a filter unless you have a problem.

I agree with Mike K.

We have some systems with high power PWM switching (50 kW or more) within a relatively short distance from the controller inside one enclosure. No special filters, no problems, it can be done.

The CNC will have line filtering itself, and will also have basic shielding so that local radio stations do not cause erroneous signals, etc.

You should be good at that distance particularly.

mike_kilroy said:

That said, there IS still potential of noise unrelated to this distance that may still get into your CNC altho it does not happen often: noise that comes out of the VFD and goes up the 220v power lines that feed the VFD. If that happens you would address it with a noise filter between your drive and the 220v source. Most installations do not require this so I would not suggest spending any money on a filter unless you have a problem.

Click to expand...

I have a 200amp main panel on the side of my house and had an electrician tap into that and ran a 100amp sub-panel into my garage which consists of multiple 220 lines as well as 110 lines.

Would this slight chance of noise comming back up the 220 line only affect other 220's or everything in the sub-panel and possible the main panel?

Sorry for my ignorance, I've never been able to get a good handle on electrical.

Also curious if my welders can cause interferance with my CNC controller as well. I think my MIG welder is OK but not so sure about my TIG as they tend to create a lot of noise.

Both welders are plugged into 220 outlets with the factory cables all coming from the same sub-panel.

Thanks in advance,
James

JST said:

The CNC will have line filtering itself, and will also have basic shielding so that local radio stations do not cause erroneous signals, etc.

Click to expand...

Is this typically true for all CNC's or just the industrial sized one's.

The one I'm getting is a very small CNC "bench" mill typically used for hobbyists and prototyping which I will be using to learn on then eventually do prototype and very small production runs with.

It's probably a good idea for me to call the manufacturer so I'll be doing that as well, just thought I ask you since manufactureres tend to tell you what you want to hear.

Thanks,
James

A CNC has a computer of some sort in it.

That, in US, is a device that "generates and uses square waves above 9 hkz", and so falls under FCC limits on interference it can produce. In order to meet that requirement, virtually any such device must have a line (mains) filter. In Europe, under EC rules for CE mark, the requirements are similar, ditto with Australian "C-tick" etc, etc. .

Most any line filter that prevents noise getting OUT, will also cut way down on noise getting IN. The parts work the same way, but the circuit may not be symmetrical going "line (mains) to load" vs going "load to line".

There are some relaxations for motor drives, so they commonly have less (or no) filtering. However, using an input inductor is sometimes done for small ones, usually required for larger, and that starts with at least some attenuation at interference frequencies.

So, you start out with some protection, and distance adds more. Conducted interference on the mains wires is probably the least likely to cause trouble. This is because of filtering, either intentional, or via the normal parts which are included in most power supplies for equipment.

I give it an under 5% chance of any trouble. I am keeping that last bit of chance "open" simply because I don't know the setup.

You can roughly test it by using an AM radio between stations, and getting close to the mains wires, as well as farther away. Tune around a bit, and probably you will find out that the radio picks up noise close to wires, but not very much at a distance. And the radio is INTENDED to pick up radio signals, so it is "wide open" to them.

of course, the radio picks up only what it is tuned to, which is why you tune dial around some. That way you probably pass over many harmonics of the drive frequency, with maximum chance of detection. Not perfect as a proof, but good for a "survey".

Thanks for the explanation JST, things are starting to make sense...atleast I don't feel like I'm looking through peanut butter any more!

James

The major issue with VFD's is that they create current and voltage harmonics down the line side of the source. This will deform the sin wave form and cause "issues" on your loads for your residence. Depends how good your VFD is versus the harmonics you will generate. A 6 pulse (more common) will develop more than a 12 pulse. VFD's w/ DC chokes on the bus and AC reactors will help also.

LarrySB13 said:

The major issue with VFD's is that they create current and voltage harmonics down the line side of the source. This will deform the sin wave form and cause "issues" on your loads for your residence. ...............

Click to expand...

As Larry says here, it "can" cause "issues" - that does not mean it definitely will cause issues. I just thought we should temper the will to maybe might.... we don't want to discourage everyone from putting a VFD on their machine in the garage or shop at home.

There are thousands of us with VFDs on 3ph motors at home without any problems with our residential other stuff. Just wanted to temper this for any new folks - we don't want to scare them off! Ha!

LarrySB13 said:

Depends how good your VFD is versus the harmonics you will generate. A 6 pulse (more common) will develop more than a 12 pulse. VFD's w/ DC chokes on the bus and AC reactors will help also.

Click to expand...

What should people look for in a VFD and what is a DC choke and AC reactor?

Also, I've been looking at machines with 5 hp, 7.5hp and 10hp motors, are there any suggestions when to stop considering VFD's where it might make better sense to go with a RPC?

Thanks,
James