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31st Jan 2015, 09:02 PM #1
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
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31st Jan 2015, 09:42 PM #2Most Valued Member
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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
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31st Jan 2015, 10:00 PM #3Cba
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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.
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31st Jan 2015, 10:14 PM #4
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
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31st Jan 2015, 10:56 PM #5
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:
Baron J.
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1st Feb 2015, 12:18 AM #6firstly 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.)
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.
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.
Thanks for the heads up with the extra resistor. If I try adding a resistor I will see if it works.
Dean
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1st Feb 2015, 08:29 AM #7All 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.
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
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1st Feb 2015, 08:56 AM #8Golden Member
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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
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1st Feb 2015, 09:18 AM #9Most Valued Member
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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.
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
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1st Feb 2015, 09:33 AM #10Golden Member
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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
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1st Feb 2015, 09:35 AM #11Cba
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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.
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1st Feb 2015, 11:27 AM #12
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.
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.
Poor and incomplete manuals are one of the major prices of using these very low cost VFD's.
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
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1st Feb 2015, 11:37 AM #13
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.
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
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1st Feb 2015, 12:07 PM #14
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
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1st Feb 2015, 12:09 PM #15Diamond Member
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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/
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