Thread: VFD Pot Dead Zone

My new VFD setup on the Woodfast lathe is working well but the Remote speed/frequency control pot has me puzzled. With a frequency range set from 20 to 90Hz I have a dead zone where the knob rotation has no effect. My query is "is a dead zone of about half of the turn (probably 100 degrees) normal?" I am using a single turn 10K pot on the Folinn BD600 series VDF but the frequency does not start to change until at around the 1 o'clock position. And I haven't found any answers in the 172 page manual. Or am I expecting too much and just have to live with it?

Any suggestions will be much appreciated.

Originally Posted by Gary H

I am using a single turn 10K pot...

Sounds like you have a logarithmic/audio taper (A) pot. You need a linear (B) pot.

Thanks, but it is definitely a Linear pot.

I have come across this before and it was something to do with the VFD parameters.
I fixed it by doing a factory reset and checked that it worked OK
Then I added my specific parameters and kept checking it worked OK.
I never did find out what it was that caused it..

Originally Posted by Gary H

Thanks, but it is definitely a Linear pot.

OK. Some VFDs can apply a bias or offset to the potentiometer input voltage. Maybe check if you have that setting?
It won't be something you can read with a multimeter. It will be an internal function.

It may be quite primitive and ignore any signal outside of what it needs to make your presets. If that’s the case, you can get around it by determining how much resistance you need between presets, pick the next size up pot and fill any elevation gaps beforehand with a fixed resistance.

Edit… having had a look at the manual online, check the wiper of the pot is attached to J11 and the J11 jumper is set for 0-10V not 4-20mA

I had the same problem Gary, this thread explains how I fixed it although it is a different make of VFD.

https://metalworkforums.com/f309/t20...ght=vfd+techo1

Thanks to all for your suggestions. So far no success, but as the only problem is the dead zone of the knob I think I'll just live with it.

Cheers, Gary

If you are using the analog input for the potentiometer it shouldn't be too hard to get it working properly although it may require a bit of trial and error. I found it a bit annoying to use when I had the dead area at the lower end of the pots travel.

Yes I am using the analog input and have tried quite a few settings. The supplier reckons it's a structural (his words) limitation of the pot. Am just using it as is for the time being and will have another go some time soon - will even try a different and maybe better quality pot and/or different size cable. Settings are minimum 20Hz and maximum 90Hz but stays at the 20 from beginning of turn to about the 1 o'clock position, then works fine from there to the maximum position (at 90Hz). Just takes very fine adjustments to get it where I want it. But at least I can use the lathe.

Originally Posted by Gary H

Yes I am using the analog input and have tried quite a few settings. The supplier reckons it's a structural (his words) limitation of the pot. Am just using it as is for the time being and will have another go some time soon - will even try a different and maybe better quality pot and/or different size cable. Settings are minimum 20Hz and maximum 90Hz but stays at the 20 from beginning of turn to about the 1 o'clock position, then works fine from there to the maximum position (at 90Hz). Just takes very fine adjustments to get it where I want it. But at least I can use the lathe.

AH HA - that's how it is supposed to work
Set minimum frequency to zero - if the pot works at full range then its all working correctly.

Why a 20Hz Minimum?
Provided you work with lighter loads you can work from 20Hz right down to near zero.
Problems of motor overheating may arise working on high loads for prolonged periods but otherwise there should be no other problems.
I use the low frequencies eg 5Hz quite often when starting tapping "through holes" eg start with a taper tap in the chuck (yes a plan old chuck) and a loose tailstock, plenty of tapping juice, start slow, increase speed maybe up to 10Hz, and then flip reverse and crank up the speed to back out.
Then swap to a middle and if needed a bottoming tap.
I cut M8s in these 16 SS (yes SS!) barrel nuts this way,
Barrelnuts.jpg

The other time I use a slow speed eg maybe 15Hz is when parting larger stock, start slowly - get the feel for teh geometry and speed and the n increase speed especialyl as the cut becomes narrower and marrow.

Have you tried setting F05.19 to around 22%? This should give the pot more range, provided that all other corresponding settings are still set to Default.

Hey, Techo1, go to the top of the class! Fiddling around with the F05.19 setting I found that the range would start at that percentage of the maximum frequency, and this got me on the right track. Now have it set at 12.5% and a maximum of 200Hz so it starts at 25Hz and I have the full range I wanted on the knob .

The reason I don't want to go below 25% Hz (slow speed) is because that would only be used on heavy, out of balance blanks - that can take quite a while and I don't want overheating, or getting hit by a big bit of timber travelling at speed!

Thanks a million for your assistance - if you're ever in Sydney drinks are on me!

Cheers, Gary

Originally Posted by Gary H

Now have it set at 12.5% and a maximum of 200Hz...

Maybe I misunderstand your settings, but is 200Hz actually selectable? I.e. with the pot fully clockwise, will the VFD output 200Hz?

This VFD has settings for Maximum Output Frequency (up to 600Hz) and for a Run Upper Limit as well. Although I have set the Maximum Output to 200Hz, the Run Upper limit is set to 90Hz and this is the highest it will go at the end of the knob range. The lower run level is set at 0Hz but the Lowest knob range is set at a percentage of the Maximum Output frequency (hence 12.5% of the 200 gives me 25Hz at the lowest end of the dial on the pot - regardless of the lower run limit set elsewhere). Sorry my earlier post was so vague - but I'll blame that on old age! And I won't guarantee this is any clearer.

The standard settings had a dead lower zone of around two thirds of the rotation. The dead zone is now around 20% - I'm happy!

I have left the original five pulleys on ( too lousy to buy new ones) but I won't be using them all. If I did, the speed would be between 155rpm at 20Hz and 4900 at 90Hz depending on which pulley was used.