Union Jubilee Clutch.

[pwdrive]

You might want to ignore my last post regarding stereo screened cable if the bottom end of the control pot is at a potential above common ground, if it is then you will need to use a multi cored screened cable or equivalent.

Lawrence.

[Retired]

Hi,

Thanks Lawrence, this screening is new to me and just looking at the various types of cable is just bewildering. I've had a look through my short lengths of cable and found the following which looks useful and should do the job? One length is twin core individually screened the second is single core but screened.

I'll need to bore another hole through the wall to accept these so a job for after dinner. the next question is what do I need to do with the screening on the cables; might be a silly question but I simply don't know; do I earth it to the supply earth on the VFD?

WOW; I've finally received a reply from the VFD seller saying my question has been forwarded to the manufacturer and they will reply as soon as any information is available; my fingers are crossed for a simple solution shortly?

Kind regards, Col.

   

[Refugee]

I have had a look at the PDF manual that was posted.
It looks like the VFD is most commonly used with a computer equiped with an RS485 port. To get as far as this the RS485 will be switched off. Just don't switch it on.
It looks to me like the VFD has the input set internally to produce the full speed range over the full sweep of the pot without an adjustment. The range is from stop to the maximum the VFD can do and not the maximum range you are calling for.
The pot offers 1 volt per 1000 revs below the stop voltage of 10 volts.
You are using just under a quarter of the full range so this means that for a full sweep control you need to use a pot that covers the range you are going to use and replace the part of the 10k you are not going to use with the fixed resistor.
To get the value you need to connect to the VFD the 10 volt stop signal needs to be reduced to the value that represents the maximum speed you want. All the pot is doing is allowing you to tap off the voltage at the rate of 1 volt per 1k of resistance and the maximum voltage below the 10 volts that represents stop you need for your speed range is about 2 volts. By selecting a 2k pot you get the 2 volt tap when the pot is about 3/4 of full sweep. The other 8k of the pot that you do not require has then to be replaced with a fixed resistor giving the 10k total resistance.
All you have to do is fit the 2k pot as you have done with the 10k pot without making the connection to the ACM terminal. Then solder two bits of wire to the 8k2 resistor and insulate it with a sleeve. Use this resistor and wire to make the connection from the pot to the ACM terminal. This divides the pot into the 2k bit you want to use and the 8k bit that you are not interested in. The VFD will work with pot values of 5k in places where there is a lot of RF noise to 15k in a nice clean area with a screened cable. The resistor in the wire can be varied between 5k and 10k without there being a problem and we will save this task until we have the wider sweep range with the 8k2 resistor in place.
We will be able to fine tune the sweep range of the pot later once you are happy with the improvement you have made with the pot and fixed resistor and you have picked up the experience from implementing it.

[pwdrive]

I'm not to sure where to earth either, in the book of words the terminal "ACM" is cited as common ground, as to weather or not that is mains earth (PME) or just a common signal rail I cannot say, might be worth checking for continuity between the ACM terminal and mains (PME) earth with everything switched off, if the ACM terminal is mains (PME) earth then connect the screens to that.

Lawrence.

[Eddystonepete]

Hi Col, you mentioned several posts ago that the 3 phase cable to the motor was screened but not earthed. This should definitely be earthed at the vfd end. If it isnt it will radiate all sorts of harmonics which could well interfere with speed control. I used the screening to carry earth to the motor/lathe although that probably isn't the "approved" method. The little oval below the pot caught me out, of course its screening. But why is it not just connected to the 0v on the pot. ?. I,d definately advise against using anything but a 10K lin pot. The answer is in the setting up somewhere. Peter

[Joe]

Caution!
Woodturning
can be
Dangerous.

It can steal away all your time,
empty your chequebook,
alienate your wife
and consume all the flat areas in your home.

Please exercise Extreme Caution!

And there are sharp tools,
flying wood and killer dust
But don't sweat the small stuff!

- Capt Eddie Castelin

[Refugee]

Lawrence is confused. The ACM terminal is the control unit 0V.
ACM is just an abbreviation for the Chinese term for 0V and that is the way it is marked up.

[pwdrive]

Lawrence is confused. The ACM terminal is the control unit 0V.
ACM is just an abbreviation for the Chinese term for 0V and that is the way it is marked up.

No, I'm not confused, I understand the difference between a common signal rail that is connected to earth ie: an isolated transformer mains radio, record player etc,
and one that is floating above any external earth ie:TV chassis were the chassis is at half or possibly full mains potential above an external earth etc, hence my previous post.
I was playing on the side of caution ie: if the potential at the V and Vin terminals on the VFD board is significantly high with respect to a PME connected to the insallation then any screened cable should be adequately rated in terms of insulation breakdown if the screens were to be connected to that PME.
As to weather the screens should be connected to the PME or the ACM terminal that's another matter.

Lawrence.

[Refugee]

We are talking about the signal grounding and the input screening would be fine there.

The mains earth will be by the mains input and aught to have links to the output screening and the frames of the machine and the motor. These are the ones you check with a PAT tester.

The signal ground will lead to the power earth but is not going to be thick enough for anything else.

[Nick]

Its very clear from the manual that the screen should be connected to the "E" terminal (mains earth) at the VFD end ONLY (else you will get a ground loop).

As mentioned elsewhere here, ACM will not necessarily be connected to mains earth - it may well float from that for noise reasons (connected via a small capacitor to provide a low Z path for HF noise).

Problem with connecting the screen to ACM is that if any significant current is induced in the screen it will appear on the controller PCB analogue ground and may make operation erratic or even damage the board,

BTW, the letters ACM stand for "analogue common".