MadModder
The Shop => Tools => Topic started by: Chazz on April 19, 2012, 04:17:19 PM
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So I want to get a potentiometer for my VFD, the question is, should it be linear or logarithmic? or does it matter?
Thanks,
Chazz
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*definitely* linear - unless you want it to crawl along until about the last gnat's and then speed up to full in the twitch of a finger...
Some VFDs (older ones, mostly) allow you to select from a bunch of different pot/speed curves, I know my (very old, but cheap!) ABB can even be configured for "joystick" pots where centre's stop, each end of travel is full speed ahead or astern.
Dave H. (the other one)
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Another vote for the Linear taper type....
When you make your purchase make sure it has the letter B after the value..i.e 10K B
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Thanks guys.
Cheers,
Chazz
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This might be of interest if the VFD's on a lathe - I've hooked up a slider pot on the cross-slide, so the spindle speed increases as you get to smaller diameters. I've found it make a big difference to the finish when facing/parting-off.
The parts are all pretty standard stuff, the slider's sprung to the minimum position and a stop on the cross-slide hits a lever which in turn moves the slider off minimum as you approach the spindle axis - result is "almost-constant surface speed", a bit like the big boys have on their CNC machines :)
The max and min pots set the range the slider changes the speed through, by setting the voltage at the max and min ends, maximum to just above half-speed on the "max" pot, Zero to a bit below half-speed on the "min" pot.
This assumes your VFD wants a 10K pot, if a different value, just scale all the resistance values!
Just my ha'pennorth,
Dave H. (the other one)