Thanks
@ttabbal
I’ll see if the seller responds.
Any recommendations for a VFD? Did I spell that correctly?
Sent from my iPhone using Tapatalk
@DavidR8
Hi David.
OK - I get it that for you, the simple 3 letters "VFD" is from another dimension!
If you want the most flexible, energy efficient, totally controllable, full torque regardless revs, power_factor_corrected, automatic soft start, internal safe-torque-off e-STOP safety, with controlled accelerate / decelerate to halt without stripping gears, then you now have loads of low-cost multi-pole (meaning 4 to 8 poles) servo drives available. Every (Jap, Chinese, American, Italian, etc.) outfit is falling over themselves to offer everything including "electronic gearboxes", and "guaranteed safety".
Will the torque force flop out?
For example - I have recently being going all weak-knee at something like -->
THIS
OK - so when we stop getting distracted, the point was how the machine can deliver a full torque controlled dead stop - zero RPM!
That is what a modern multipole servomotor with encoders can do - and motors don't have to be a DC type.
I have listed only 7 features so far. Now consider what "VFD" used to mean.
Variable Frequency Drive! So now let us carefully lead you into what this might mean. I will try to make it meaningful for anyone who glazes over when encountering business buzztalk like "fully integrated solutions for fully parameterized high-bandwidth current-loop stability"! Ditch all that for now.
Motors? "Induction" motors? ..
Take the most common motor type. From decades past to the present, it is only now that we are finally getting some really serious motor development, like the 185kW motor in the back end of the Tesla Model S, For the average small(ish) lathe, it is a 3/4 HP or 1HP "squirrel-cage" induction motor. If you use both phases in a USA-type supply (2 x 110V = 220V or so), you can have 2.2 to 2.9kW - i.e. up to about 3HP. They can be artificial 3-phase, or an artificial 2-phase which starts out as single phase, and the "other" phase is made by putting it through a capacitor, often seen as the "extra" cylindrical component hanging on the outside of the motor. If you have an "older" piece of iron that hails from the days before software-controlled everything, then this is very likely what came with your iron.
You can "change the speed" of these by making an electronically generated artificial supply, and "make the frequency less than 60Hz". The motors middle bits, "armatures, rotors" whatever, rely on a magnetic field that "rotates". I skip over what exactly is "induction motor" for now. Suffice to say it is the way the rotating bit manages to become magnetic is by having the field "induced" in it - much like a transformer.
It is simply not enough to just change the frequency, which is already low to start with. The torque force drops off dramatically!
Also note that the spinning bit does not manage to keep up with the rotating fields coming from the coils. There is always a "lag", which gets bigger as you load the motor.
Speed and Torque
Now we come to the crucial bit. The power delivered by the motor is Power = Torque x Speed. In this case, "speed" is an angular velocity, which can expressed in terms of RPM using conversion constants e.g. HP = Torque (pound-foot) X RPM/5252. The point is - look what happens if you want to go slow! The power falls to zero! This is the main disappointment if you have a simplistic "VFD" simply plonked straight onto an old induction motor.
Better types of VFD.
Still going with the available VFD's, the better types are still able to drive single phase and three phase induction motors with better delivery of torque at slower speeds. They generate an artificial 3-phase supply, or two phase for use with an old motor, and you ditch the capacitor. This can be had from a single phase source. Be aware that there is a limit to how high a voltage you can wring out of a 110V supply. If you can get across the two phases as most US-type household supplies are done, for 220-240VAC, and connect the artificial 3-phase in a wiring mode known as "delta", you can extract a respectable amount of controlled power. These sort only alter the frequency by a limited amount. They operate the motors with large amounts of "slip", and they alter the energy to the coils using quite complex higher frequency pulsed waveforms. Higher frequency means about 2kHz to about 20kHz, though any carrier below 8KHz squeals to annoyance! Welcome to "variable duty-cycle pulsed-width modulation".
So we have many products, all using the simple moniker "VFD", and we now know that some are more capable than others. If you intend to keep the old induction motor, make sure the VFD you choose will drive it, and try and discover if it will deliver enough torque to take the heavy cut, even though you are turning slow. Some of these get very clever. Unfortunately, too many are simply vague about the detail of what the drives really will do.
If I wanted high torque full speed control, I would try for a modern permanent magnet multi-pole motor with shaft encoder, and programmable servo drive, which might all simply go under the name "speed control", These encoders can count all the pulses from the encoder that might happen in decades of turning. They can be used for
positional control. Welcome to CNC.
Modern VFDs are clever enough to get by without an encoder. They can sense the currents in the coils. The torque control is not as tight, or as precise, but it removes an expensive component, and may be all you need for regular non-CNC work.
Forgive that I may have just muddied the waters for you. My background includes designing 2 x 70kW servo drives for a 60HP RAT turbine that could receive and deliver program demanded revs and torque either pumping or being pumped by jet fuel, and return incoming power to the grid instead of dumping it in a heater. I did not miss the point that the humble induction motor on my
South Bend 9A needs either a damn smart "VFD", or should be replaced by a modern drive motor. The innards of these things are still very physics-fundamenrtal. Just metal and copper and insulation and (now) powerful magnets. Add bearings and shaft. They do not cost substantially more than the old kit unless you are being offered hype! The real smarts are in the drive controllers, often using high-speed 32-bit internal computing.
Now try and make it simpler
1. First decision is whether to play with the full servo motor replacement deal, or whether to find some electronics that will make the old induction motor deliver a reasonable facsimile thereof. If you want to use the induction motor, then pay attention to the detail claims of the drive, especially if it calls itself a "VFD". There are some good ones about, made specifically for traditional induction motors, but quoting "Animal Farm", "some are more equal than others. You know now to check whether it can haul up a high torque at 100RPM. Look for features like "Power Factor Correction" , and "RFI filtering", and the presence of a load dump resistance load for acceleration and braking control.
2. The next thing is to check the power input capabilities. Know your AC mains supply, and what the drive expects. Figure out the power.
3. Take care about the motor capabilities. An AC capacitor on an old 60Hz induction motor may not take kindly to a 12kHz carrier pulse-width modulated drive unless the waveform envelope approximates a traditional 60Hz supply, even if the shape is more "square" than "sine".
It can be a complicated subject, and I get it that you want to see straight to an affordable product that can bolt-on. I think they exist, but I was not going there. I have tried to cut through the jargon, but it still ended up a long posting, for which I apologise.
edit: P.S. Just for curiosity, what are the available voltages in a Canadian-type supply. Do you get 2 phases to a household, so higher energy stuff like cookers etc. can have 220-240V? What motor do you want to get adventurous with?
