Wired potentiometer to VFD, not using the full motion range of pot.

Domodude17 · Mar 19, 2021

I have a Teco L510 VFD wired up to my lathe, 3/4hp 3 phase motor. I've got it set to operate between 0hz and 100hz max. I have a 5k ohm potentiometer from Automation direct I wired in to control the speed. At the full left position, the motor is at 0hz. Turning the pot, the motor reaches the max frequency through maybe 70% of the travel. so once the motor is at max frequency, the pot can continue to rotate further without anything happening. I'd like to adjust it so full left is 0hz, and full right is 100hz.

Does anyone know if there's a fix to this? Maybe a setting in the VFD somewhere? I have looked through the manual but didn't see anything that immediately jumped out at me.

Thanks in advance!

Brandenberger · Mar 19, 2021

Domodude17 said:
I have a Teco L510 VFD wired up to my lathe, 3/4hp 3 phase motor. I've got it set to operate between 0hz and 100hz max. I have a 5k ohm potentiometer from Automation direct I wired in to control the speed. At the full left position, the motor is at 0hz. Turning the pot, the motor reaches the max frequency through maybe 70% of the travel. so once the motor is at max frequency, the pot can continue to rotate further without anything happening. I'd like to adjust it so full left is 0hz, and full right is 100hz.

Does anyone know if there's a fix to this? Maybe a setting in the VFD somewhere? I have looked through the manual but didn't see anything that immediately jumped out at me.

Thanks in advance!

I don't know those VFDs, but it looks from the manual like you should have 10v input to the speed pot, and you need 0-10v output back into the drive. Can you put a DMM on it and see what you're getting at various points on the travel of the pot wiper?

Note: I'm assuming if you set the VFD to use the on-board potentiometer you get the full range as you would expect?

jmm03 · Mar 19, 2021

What is your setting on parameters 00-11,00-12, and 00-13 ? Jim

JST · Mar 19, 2021

There may be a setting to adjust the voltage range, or to "scale" the input. Check and see.

You first need to check the voltage. It is not unknown for certain "tapers" of pot to have largish dead areas at one or both ends of the rotation. A "reverse audio" taper will change rapidly, then slowly, and could seem or even be as you describe.

So be sure what the voltage output is as the control is rotated.

Also be sure you are on the correct voltage source. Many or most will have a regulated 10 V, but will also have 15 or 24 V available for other purposes. If you were connected to 15V, that would do something similar.

Yan Wo · Mar 19, 2021

Did you wire the pot one side to +10, other side to ground, and center to VFD frequency set input?

Domodude17 · Mar 19, 2021

00-11 is set to 60hz. 00-12 is set to 120hz, and 00-13 is set to 0hz.

The pot has a dedicated 10v power source, I measured it at 10.5v. At full left (off) I measured 0v, and at full right (on) I measured 10.5v.

The potentiometer is wired as you describe.

I tried setting the max frequency to 120hz to see if it would use the extra range on the pot, which it did not. It reached max frequency at approximately the same position. I checked the voltage in this "dead zone" and it did adjust down from 10.5v. The built in pot does adjust from 0 to 100 hz using the full range.

Is it possible the VFD is looking for a max of 10v, so when the pot reaches 10v at a slightly lower position, it assumes that's the max position?

mksj · Mar 19, 2021

Check the linearity of the pot, make sure it is not a log pot, it needs to be linear. You also may try a different speed pot say 2Kohm

Parameters to check/try
00-05 2:External AVI Analog Signal Input
00-06 2:External AVI Analog Signal Input
00-07 0: Main Or Alternative Frequency
00-11 60: is the initial keypad frequency but would be ignored with the above parameters
00-12 120: Frequency Upper Limit set to maximum frequency desired should match 01-02
00-13 2: Frequency Lower Limit Set to something like 2 Hz should match 01-08

Set the 02 motor parameters

Section 04-00 deals with analog voltage input selections and how they correlate to the 0 to 10V input range. Read this section which might give you some insight to adjust the external speed input parameters.
04-02 is the AVI Gain which will set the slope of the gain, default should be 100% which would correlate to 10V, you could try 80 or 90%, but this should correlate to a proportionally lower maximum speed.

04-11 defines the Xmax dependency, in theory selection 0 (default) uses the output frequency; or you could try 1 frequency command setting to set the upper limit; or one could try 2 which is the output voltage (motor rated voltage)

JST · Mar 19, 2021

Domodude17 said:
..................

Is it possible the VFD is looking for a max of 10v, so when the pot reaches 10v at a slightly lower position, it assumes that's the max position?

Well, yes. If the pot voltage goes over the max input voltage for the control input, the amount of voltage (and control travel corresponding to a voltage over max) normally will be ignored. That is why I asked about the pot voltage.

The voltage is normally a bit high to make sure that you can get full voltage and speed. If that is a problem you can choose a resistor to put in series with the pot, between the voltage and the "top" of the pot which will bring the max voltage from that particular control pot down to the voltage for maximum speed. Then the pot will have full range.

A half volt is only about 5% of the total, so if the rotation is 30% short, there may be another issue, and the resistor would not be a solution. I do not think that is your issue.

ITEMS TO DO:

Check the actual voltage which is produced at the pot output at full rotation, at 1/2 rotation, and at no rotation (zero). Also what the voltage is with the pot set to where the "dead zone just starts when you turn the pot for higher speed. Report those 4 voltages here. That will show what sot of pot it is, and whether there is a pot taper issue, or something else.

Strostkovy · Mar 22, 2021

Reverse the positive and negative leads to the pot. If the deadband is now at the low frequency instead of the high frequency then you may have a potentiometer meant to have a switch mounted to the same shaft.

If that is not the case, and there are no settings to scale the input that you can find, you can put a 2k multi turn trimpot in series with the positive and the potentiometer to dial in the upper range (and lower, if starting at too low of a frequency is a stall issue). These types of "trimmers" are not meant to be turned often but are cheap and hold their resistance value long term.

A trimpot will not correct linearity, if you have a potentiometer meant for audio applications. A link to what you purchased from automation direct will let us further assist you.

Domodude17 · Mar 23, 2021

Sorry about the lack of updates, I haven't had time to look at this lately. The pot I purchased is linked below. I didn't see anything about it being linear or logarithmic.

https://www.automationdirect.com/ad...dicators/22mm_metal/potentiometers/ecx2300-5k

I measured the resistance, and it turns out the pot is actually 2kohm. I will take a look at some of the settings suggested above, particularly the gain that was mentioned. Thanks all!

mksj · Mar 23, 2021

Pot is suppose to be 5K not 2K and it is linear. You might have the speed pot connections wrong, the speed pot terminal 1 goes to AGND, terminal 2 goes to AVI and terminal 3 goes to 10V. You should measure 5K between terminal 1 and 3, measuring ohms between terminals 2 and 3 should read 5K at 0 and a few ohms at 100% (around 300 degrees rotation).

rons · Mar 23, 2021

I should have started a potentiometer business.

Strostkovy · Mar 23, 2021

mksj said:
Pot is suppose to be 5K not 2K and it is linear. You might have the speed pot connections wrong, the speed pot terminal 1 goes to AGND, terminal 2 goes to AVI and terminal 3 goes to 10V. You should measure 5K between terminal 1 and 3, measuring ohms between terminals 2 and 3 should read 5K at 0 and a few ohms at 100% (around 300 degrees rotation).

I don't think he has the connection wrong simply because if he connected it any other way the resistance between power and ground would get mighty small at one end of the pot.

Maybe it would just drag the VFD output down but I feel like it would alarm on that.

It is startling to say the least when your controls catch on fire.

Domodude17 · Mar 23, 2021

An update from some more testing this evening: I played around with some of the AVI settings-gain, slope, slope inclination, etc to no avail. I also double checked the "lost rotation", I think I'm at about 85% rotation used.

Starting to seem like a trimmer pot will be the way to go, or at the very least a custom data faceplate with some of the numbers shifted lol

SomeoneSomewhere · Mar 24, 2021

Bumping up 04-02 'AVI Gain' to 120% or so should do it.

It looks like you should be able to step through the display and read out the current input value in percent (e.g. '085P') - what does it tell you?

Is it possible it's just set to 50Hz not 60Hz and it thinks it's at full speed?

atomarc · Mar 24, 2021

I re-read the original post and I really don't understand what difference it makes with the rotation of the pot. The max RPM is set on the drive, so that's all that's achievable with the pot, regardless if it turns a bit more. Any movement of the pot that doesn't increase the spindle speed is obviously dead band. When you reach a position that doesn't increase spindle speed you know you're at the max drive RPM.

Sorry if I'm missing something.

Stuart

JST · Mar 24, 2021

atomarc said:
I re-read the original post and I really don't understand what difference it makes with the rotation of the pot. The max RPM is set on the drive, so that's all that's achievable with the pot, regardless if it turns a bit more. Any movement of the pot that doesn't increase the spindle speed is obviously dead band. When you reach a position that doesn't increase spindle speed you know you're at the max drive RPM.

Sorry if I'm missing something.

Stuart

It really only matters in that the full change or speed is over less than full rotation, so setting speed is a little more difficult. You get only 70% of rotation (so stated, IIRC) to cover the range and not the full rotation.

Obviously the speed range is fixed and so any overage has no effect.

Since the voltage supplied is 5% over, but the pot rotation is considerably more, it does not seem as if that is the issue. It must be a different problem.

jmm03 · Mar 28, 2021

Domo, out of curiosity, have you found a solution to the original issue? Jim

Domodude17 · Mar 29, 2021

jmm03 said:
Domo, out of curiosity, have you found a solution to the original issue? Jim

Sorry for the delay all, I haven't had much time in the shop as of late. I did some more investigating, and found that i'm only losing about 15% of my travel, not as much as I had previously thought. When I played around with the settings such as gain, I didn't see any change. I'm thinking that if I decide to actually fix the issue it'll almost certainly be a trimmer pot to cut down the max voltage to exactly 10v. If I want to be lazy about it ill just use a marker to draw some lines on the control box next to the pot itself, and use those as my frequency references.

atomarc · Mar 29, 2021

This may not apply in your situation, but almost all frequency drives have the option to toggle the display between HZ and several different readings. If the drive is located somewhere that you can read the display while you operate the machine, it would be a simple thing to actually read the selected display versus guessing at it or looking for sharpie marks on a knob. Just a thought.

Stuart

Wired potentiometer to VFD, not using the full motion range of pot.

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