Thread: Multiturn Variable Resistor for a VFD Remote

When I was in the final stages of setting up my lathe to run with the VFD I discussed the idea of using a Multiturn Variable Resistor to control the motor speed. At the time I ordered a couple as well as the counting knobs (?). These have been sitting on a shelf since then. Last weekend I decided to try one.

It worked fine except that it did not give the full range of speed that the normal pot did. Maximum resistance was measured about the same as the removed pot. They are both 10k ohm, but measured a bit under this. What I can do now is to set a pretty accurate motor speed by simply dialing in on the pot. Much more accurately than previously.

I have been wondering how to get a greater range of speed. The Multiturn VR provides a maximum speed of about 50Hz. It is a 10 turn pot. The first 8 turns do next to nothing. Working on a minimum usable speed of 15Hz I worked out the position of the pot at this point. Setting the other spare pot to the same position I measured its resistance and determined that there was about 5k of unused resistance up to this point.

I then thought that if I added a 4k7 resistor in series, this should move the usable range of speed back to the previously unused portion of the multiturn pot and provide more speed range at the higher resistance end.

I may be totally wrong here as I am no expert in this field. Can anyone comment on my ruminations.

Dean

You didnt buy a log pot did you*? I GUESS they would act something like that. If thats the case I dont think you can do much to increase the useable range.

Stuart

* dont even know if you can get 10 turn log pots

Dean,

firstly I do not think that a 10 turn pot is a good idea for a vfd. It takes far too long to change speed. Even a 2 turn pot would be out of question for me. But this is your choice to make.

That said, if the 10-turn pot is 10k and the standard pot is 10k, and both are linear type (I actually have never seen a logaritmic 10 turn pot.....), they will both provide the same speed range. Provided you hook them up the same way (pots have 3 connections, and with multiturn pots the variable tap is not always in the middle! There often is a diagram printed on the pot body and the connections are numbered.)

All the VFD's I have recommend a 1k or a 2k pot. 10k is rather high, and depending on VFD make could possibly pick up noise if fitted with long control leads between the pot and the VFD. With most VFD's there are 12V DC across the speed pot, and the speed control happens by the pot varying the control voltage from 0 to 12V. Most mordern VFD software lets you program which control voltage will correspond to minimum and maximum frequency, and you can additionally limit the minimum and maximum frequencies.

But check first if you mixed up the pot connections, it sounds much like this is what happened.

Originally Posted by Stustoys

You didnt buy a log pot did you*? I GUESS they would act something like that. If thats the case I dont think you can do much to increase the useable range.

Stuart

* dont even know if you can get 10 turn log pots

The thought did cross my mind. I had another look on EBay to see what was available other than the 10k ohm, but all I saw was a 2k ohm. The listing currently on EBay gives the following information

"Feature:10K Ohm Resistance, 5% Tolerance,0.25% Linearity, 3 Terminals Multiturn Potentiometer."

I guess that means it is a linear pot. No guarrantee that this is actually the one I bought tho.


........

I just went out and looked. Same pot. Linear. Measured at 10.22k ohm (This is the spare) The removed pot was 8.1k ohm.

Adding the 4k7 ohm resistor as mentioned, I am hoping will move the usable range. I did also wonder about a hi/lo switch to switch this resistor in and out of the circuit, but dropped the idea when I realised how little of the range was actually being used.

Dean

G,morning Dean,

I agree with the suggestion that you have a "log" pot. Your Idea of sticking a 4k7 in the bottom end will work but not quite. You might need to put another resistor in parallel (right across the ends of both the pot and added resistor) to pull the overall value back down to around 10k.

Lets see if I can remember how to do this. Its years since I last did this...

1/10,000 = 0.0001 and 1/15,00 =0.000066r so subtract one from the other gets me 0.000034, so 1/0.000034 = 29k4 If I've got my sums right a 27k resistor should do it.

firstly I do not think that a 10 turn pot is a good idea for a vfd. It takes far too long to change speed. Even a 2 turn pot would be out of question for me. But this is your choice to make.

That said, if the 10-turn pot is 10k and the standard pot is 10k, and both are linear type (I actually have never seen a logaritmic 10 turn pot.....), they will both provide the same speed range. Provided you hook them up the same way (pots have 3 connections, and with multiturn pots the variable tap is not always in the middle! There often is a diagram printed on the pot body and the connections are numbered.)

10-turn was all I could find at the time. I wanted less, but having said that only the last 2 turns or so are actually needed. I am not sure what your issue is with multiturn. From my point of view it seems like it would be faster to dial in a known value than making adjustments, waiting for the speed to settle, making more adjustments etc, etc.

Both pots are Linear 10k. According to the diagram the variable tap is in the middle so it is connected correctly. I did check this with a meter. I assumed the loss of speed range was caused by small variations in the max resistance as at this point the response from the VFD is sensitive. I will try the spare VR pot and see what happens.

All the VFD's I have recommend a 1k or a 2k pot. 10k is rather high, and depending on VFD make could possibly pick up noise if fitted with long control leads between the pot and the VFD. With most VFD's there are 12V DC across the speed pot, and the speed control happens by the pot varying the control voltage from 0 to 12V. Most mordern VFD software lets you program which control voltage will correspond to minimum and maximum frequency, and you can additionally limit the minimum and maximum frequencies.

It is only the top of the resistance range that produces viable motor speed. The leads are sheilded with the +10v connection thru the sheild. Looking at the programming could be another way to deal with this.

G,morning Dean,

I agree with the suggestion that you have a "log" pot. Your Idea of sticking a 4k7 in the bottom end will work but not quite. You might need to put another resistor in parallel (right across the ends of both the pot and added resistor) to pull the overall value back down to around 10k.

Lets see if I can remember how to do this. Its years since I last did this...

1/10,000 = 0.0001 and 1/15,00 =0.000066r so subtract one from the other gets me 0.000034, so 1/0.000034 = 29k4 If I've got my sums right a 27k resistor should do it.

Best Regards:
BaronJ.

Hi Baron.

Thanks for the heads up with the extra resistor. If I try adding a resistor I will see if it works.

Dean

All the VFD's I have recommend a 1k or a 2k pot. 10k is rather high, and depending on VFD make could possibly pick up noise if fitted with long control leads between the pot and the VFD. With most VFD's there are 12V DC across the speed pot, and the speed control happens by the pot varying the control voltage from 0 to 12V. Most mordern VFD software lets you program which control voltage will correspond to minimum and maximum frequency, and you can additionally limit the minimum and maximum frequencies.

Can anyone point me to the right parameters for this purpose, on a Huanyang VFD.

I have found pd027 and pd028. Starting and stopping freq. I find it difficult to understand the manual, and why reinvent the wheel?

Cheers

Dean

Dean i wonder if you need to raise the upper frequency limit( not the start stop freq) parameter. I have several vfd s some huanyang and 10 k pot works fine somewhere Ive filed my documentation of the settings i used but where
john

Originally Posted by Oldneweng

From my point of view it seems like it would e faster to dial in a known value than making adjustments, waiting for the speed to settle, making more adjustments etc, etc.

The leads are sheilded with the +10v connection thru the sheild.

Hi Dean,
if you're just worried about the time the display takes to settle, there is a setting for this. PD71 I think it is. This does effect the output in any way, the vsd will still ramp as per the other settings but the freq display will 'folloew the pot' faster(or slower)
As far as shielding goes, if you are using the shield for your +10V supply, I'm not so sure that will work.

Originally Posted by Oldneweng

Can anyone point me to the right parameters for this purpose, on a Huan

PD072 or PD073 gives max and min pot freq, thought I wouldn't like to say which is which as I think my manual has them ass about.

Stuart

stuart i just found a bit of paper with the parameters

72...........70
73........... 5

if i recall it was 70 hertz upper limit and 5 lower limit

if these parameters are still at factory setting maybe why the pot wont vary the frequency by much
john

Originally Posted by Oldneweng

Can anyone point me to the right parameters for this purpose, on a Huanyang VFD.

I have found pd027 and pd028. Starting and stopping freq. I find it difficult to understand the manual, and why reinvent the wheel?

Cheers

Dean

Dean,

- the addition of any resistor to your potentiometer, can only reduce the available speed adjustment range!
- you need to work with the parametes. Someone with Huanyang experience has to help you, I have always avoided these. Poor and incomplete manuals are one of the major prices of using these very low cost VFD's.

Originally Posted by tanii51

Dean i wonder if you need to raise the upper frequency limit( not the start stop freq) parameter. I have several vfd s some huanyang and 10 k pot works fine somewhere Ive filed my documentation of the settings i used but where
john

That was just the first step of the journey. It is at least related to motor speed.

Hi Dean,
if you're just worried about the time the display takes to settle, there is a setting for this. PD71 I think it is. This does effect the output in any way, the vsd will still ramp as per the other settings but the freq display will 'folloew the pot' faster(or slower)
As far as shielding goes, if you are using the shield for your +10V supply, I'm not so sure that will work.

Thanks Stuart. That will make things much easier. What I would like is a display like a few of the pumps at work. These show the pot set frequency at all times so you can adjust the speed without turning the motor on. Does this occur with the parameter mentioned. I will find out for myself shortly anyway

Dean,

- the addition of any resistor to your potentiometer, can only reduce the available speed adjustment range!
- you need to work with the parametes. Someone with Huanyang experience has to help you, I have always avoided these. Poor and incomplete manuals are one of the major prices of using these very low cost VFD's.

I would have thought that was the case ordinarily, but why then is my VR limiting the speed. If full speed is acheived with zero resistance there would have to be resistance somewhere in the wiring. I did check the VR to determine which way to wire it. I would prefer to work with the parameters. I am going to go and check the resistance of the VR and wiring and try the parameter changes and maybe my spare multiturn VR as well.

Poor and incomplete manuals are one of the major prices of using these very low cost VFD's.

Indeed. That is why I am asking this question here.

The very low cost aspect is one of the advantages for someone like me. I have decided to try and replace this VFD with a bigger one, as it will only go to a bit above 80Hz before it goes into overload protection and shuts off power to the motor. The motor is a 2 speed so running the VFD at 100Hz in delta is only doing what the lathe is designed to do. The current VFD is a 4kw unit. I would like to get a 7.5kw unit. This is going to be expensive. I guess I can take my time and look for a bargain. Single phase input VFD's of this size are thin on the ground.

Dean

Originally Posted by tanii51

stuart i just found a bit of paper with the parameters

72...........70
73........... 5

if i recall it was 70 hertz upper limit and 5 lower limit

if these parameters are still at factory setting maybe why the pot wont vary the frequency by much
john

This has already been adjusted upwards. I was getting much higher frequency before the VR change. It is the VR and maybe wiring that is causing the limit. The VR is at max.

As far as shielding goes, if you are using the shield for your +10V supply, I'm not so sure that will work.

Stuart

All the shield needs is a current flow. This can be changed of course, but I chose this one because it is the supply connection. It should have a current flowing whenever shielding is needed.

Dean

HI Dean,

No reason a 10 turn pot won't do what you want. The first thing to understand is that it's not resistance per-se that controls the speed, it's voltage at the control terminal, what that voltage means in terms of speed is determined by the drive configuration.

Select external terminal PD02 = 1
Select 0-10V Analog Control PD70=0
Select Lower Analog Freq PD73=5.00 Hz
Select Upper Analog Freq PD72=100.00 Hz

As Stuart said, I have a feeling those two might be reversed, that is PD72=lower freq, PD73=upper freq

Also check that you are getting 0 to 10 volts at the pot wiper and that it's linear with pot rotation.

Ray

If you don't mind paying a bit more than Ebay prices, RS Components and Element 14 have a decent range of 3 and 5 turn pots such as this one:

http://au.rs-online.com/web/p/potentiometers/4601893/