# Human Antennae



## Skye1234 (Feb 7, 2013)

Got an interesting problem and was hoping someone had an explanation for it:
I have a very sensitive control device that acts as a thermostat/wall controller connected to a 2HP, 230V single phase AC Tech: SM Vector VFD. The wall controller is powered by a 120V circuit, which is then stepped down to 16VDC. The wall controller sends a 4-20mA signal to the VFD depending on the speed setting to control the motor. 
The problem is that another motor (2HP, 230V Three phase Delta-E/ Nidec 2HP 1.5KW motor) while running, is returning a signal through it's Line Side and back to the panel. From the panel the signal is continuing on to the 120V dedicated circuit for my wall controller. This, so far, is not effecting the controller until anyone touches it. 
I could understand this signal disturbing my controller, but the fact that it does not until a person touches the controller has me stumped. 
I know for a fact it is the Nidec motor causing the problems, as I can either shut the motor off while the VFD is running, or connect the controller onto a different distribution panel and the problem is gone. 

Any thoughts?


----------



## Big John (May 23, 2010)

I hate to be the guy who says "I think it's a grounding issue" but I think it's a grounding issue.

How are the shields for your 4-20mA circuit terminated? And have you put a loop calibrator on to actually watch what is happening to the control current when someone touches this controller? What voltage measurements have you taken?


----------



## vinister (Apr 11, 2012)

what are you using to step down the 120 to 16VDC? Nothing should be getting through it... it should be clean 16VDC. 

I don't think the human is grounding the device... but it might help to run a ground from the case of your device to your ground bus.

The human antenna issue is possible, but that motor would have to be putting out some serious RF, in which case I would say there's something really wrong with that motor!


----------



## JRaef (Mar 23, 2009)

The Nidec motor is NOT on the VFD then?


----------



## Peewee0413 (Oct 18, 2012)

If someone touches it and it goes nuts, it seems like grounding..how's the shielding landed? The transformer should stop the VFD interference ...maybe ...might be at the signal wire


----------



## Skye1234 (Feb 7, 2013)

Sorry it took so long to reply, been on the road.
I have a revision to make. If I connect the 16V supply to any other power source it still does this. UNLESS the Nidec motor is disconnected.
I am beginning to think that it could be a flux being sent out from the motor. 
I have tried everything involving grounding/bonding and it did nothing. 
I have tried to upgrade my drain cable and nothing. 
I am at a loss. 
The only time this happens is when the Nidec motor is running and a person touches the controller or sometimes walks by. 
I have hooked up 3 additional motors, 1 more Nidec and 2 Bonfiglioli motors. Regardless of which of these or if all of these are running I still get the same issue, but within a 15' range. 
On another note, the controller does not need to be hooked up to a motor for this to happen, just on and to any random VFD my heart desires.


----------



## Skye1234 (Feb 7, 2013)

The shielding is landed in the controller. I have tried hooking the drain up in my VFD instead of the controller and I still get the same issue. I even purposely created a drain loop hoping that some magic might occur...


----------



## Peewee0413 (Oct 18, 2012)

I only see interference in signal wire if directly next to med/hi voltage cable and improper drain landing ( less than proper ground)....good luck


----------



## Skye1234 (Feb 7, 2013)

Yeah, but my signal wire is ran about 15' apart from my supply circuit.


----------



## xlink (Mar 12, 2012)

I'm not sure I understand all the variables, but have you thought about meggering the motor?


----------



## Big John (May 23, 2010)

Skye1234 said:


> ...The only time this happens is when the Nidec motor is running and a person touches the controller or sometimes walks by....


 So this will command a VFD to change speed when someone just walks by the stupid thing, and that's the only thing happening? Are you 100% certain of that?

I don't have an explanation, but if it was really that glitchy, I would not hesitate to simply not use that model or brand.

I might give them the benefit of the doubt and call tech support, because it sounds like you've covered all obvious ideas. The business about "motor flux" doesn't really sit well with me: I wouldn't expect a standard induction motor to introduce any excessive noise into a system.


----------



## Skye1234 (Feb 7, 2013)

No, only because I have 4 motors doing the exact same thing. I can get more if I desired, but they will do the same thing.


----------



## Skye1234 (Feb 7, 2013)

Unfortunately, yes I am positive. It has happened three times so far. Like I stated, it is pretty rare for it to happen, but then again three times within a few hours is not that rare.


----------



## Skye1234 (Feb 7, 2013)

Any other time, it happens when I touch the controller and a nearby motor is on. 
The reason I ask about flux is that it stops if I get around 20' away from the nearest motor.


----------



## Big John (May 23, 2010)

Do you have a part number for this controller?


----------



## Skye1234 (Feb 7, 2013)

At first I thought it was a static discharge from me to the controller components, but nothing seems to be damaged and any type of bonding or grounding of myself does nothing.


----------



## Skye1234 (Feb 7, 2013)

I can possibly get it. It is not an issue in the field, as our motors are usually close to a hundred feet away. I just want to know how this is happening so we know what, if anything, to avoid.


----------



## Skye1234 (Feb 7, 2013)

Sorry if an ad just popped up in my last post.


----------



## xlink (Mar 12, 2012)

Maybe a system ground problem. Poor grounding or multiple grounds on the neutral causing the grounds to carry current?


----------



## xlink (Mar 12, 2012)

If you are an antenna, maybe the source isn't in your hands but at your feet.


----------



## Skye1234 (Feb 7, 2013)

Yeah, I thought of that one. I tried using a double insulated mat about 1/2" thick. It worked for a few seconds, but then ramped up to 100% again.


----------



## xlink (Mar 12, 2012)

I was thinking a mat bonded to the controller so your feet and hands would be at the same potential. 

Are you an AM or an FM antenna? I've had problems with FM hand held radios causing problems with drives, so I'm guessing FM. What station?


----------



## John (Jan 22, 2007)

Did you look at the 16vdc to see if it bonded to ground?


----------



## Peewee0413 (Oct 18, 2012)

If you haven't found it now call the ghostbusters. You only have a couple places to get interference. Look harder and try different grounds/drain location. Run a ground wire somewhere else. Isolate the dc ground. Doubt its the vfd, I run signal wire to vfds all the time. I dunno bro. Bet its a five minute fix when u find it. Is your controller bad?


----------

