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
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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