Looking for answers again

[ltlvt]

The pictures showing my VFD inside the control panel of my McLane mill. Question # 1 is what do I connect the shield wire to? Is it supposed to be grounded on both ends or just one end and if so which end. Question # 2 is the VFD instructions call for a 5k Ohm Pot and what I have is a 10k Pot. I have used the 10k to prove the VFD works but am unsure if I should leave it or use a 5k. Is it safe to use the 10k and if so, will there be any difference in the speed of the motor? Thanks in advance.

 

[Reddinr]

Generally, connect the shield lead only on one end. I would connect it to a ground screw on the VFD end.

The 10K is likely "safe". I don't know if you are getting the full range available from it but probably. A 5 K may be less susceptible to electrical noise but really not by much.

 

[Eddyde]

Correct, ground the shielding only on the control end.

Edit, I interpreted it backwards.
Best to use a 5k pot, they are cheap enough, the 10k would be more resistance then the circuit is designed for so in might not be good.

 

[Eddyde]

Using the 10 K you would hit 5k in only about half a turn of the pot, you probably wouldn't see much, if any, speed change after that.

 

[ltlvt]

Correct, ground the shielding only on the control end.

Edit, I interpreted it backwards.
Best to use a 5k pot, they are cheap enough, the 10k would be more resistance then the circuit is designed for so in might not be good.

Thanks, I will get a 5k ordered before completing the connections. When you say control end is that the VFD end or the POT end?

 

[Winegrower]

Most good designs would use the pot as a ratio device, not as an absolute resistance. I expect the 10K pot would work fine and give full control of speed.

 

[Eddyde]

Thanks, I will get a 5k ordered before completing the connections. When you say control end is that the VFD end or the POT end?

Sorry, I should have been clearer, I meant ground everything at the control system, in this case the VFD. Terminate the shielding about a half inch back from the pot end and cover with heat-shrink tubing or tape. The general rule is to ground everything at one place, to prevent ground loops.

 

[Eddyde]

Most good designs would use the pot as a ratio device, not as an absolute resistance. I expect the 10K pot would work fine and give full control of speed.

Yes, I believe you are correct. I suppose the method could be determined if the VFD needs all three wires from the pot or just two. The latter would be measuring just the resistance.

 

[Ulma Doctor]

You could use a 20k potentiometer if you want- it’s not correct but not detrimental to the VFD
the potentiometer would only control the speed from 0 to 5,000 ohms .
or about 1/4 of the potentiometers’ travel.
A 10,000 ohm potentiometer will have about 1/2 of its travel for speed control .

 

[WobblyHand]

You could use a 20k potentiometer if you want- it’s not correct but not detrimental to the VFD
the potentiometer would only control the speed from 0 to 5,000 ohms .
or about 1/4 of the potentiometers’ travel.
A 10,000 ohm potentiometer will have about 1/2 of its travel for speed control .

It all depends on how it is wired.

If just two wires, you are correct.

If all three connections are made, the pot is probably being measured ratio-metrically, and a 5K, 10K or 20K will probably work fine.

In ratio-metric mode, power and ground are applied to the end points of the pot and the wiper voltage is read by the circuit. The wiper voltage will be the same, no matter what the total pot resistance is, at the same wiper location. The current through the pot will change, but not the voltage.

To make a more concrete example, say the power supply is +10V. So there is 10V across the whole pot resistance. If the wiper is at the midpoint, the wiper voltage will be +5V, no matter if the pot is 1K, 5K, 10K, or 50K. You do want a pot that is close to the original, but don't sweat the actual resistance.