Hello

I want to convert my lathe from 1/4hp single phase 120v to variable speed 3phase and I have a 1/4hp 208/230/460v 3Phase motor. From my research I have read that I do not need an inverter duty motor as I will run 230v into a motor rated to handle 460v (should be OK with spikes). My thinking is I will use a 115v single phase in / 230v three phase out - 1hp VSD as I may later upgrade to a 1/2hp motor and I feel I will get more life expectancy by over sizing and adding airflow via a small fan.

I have read about v/hz control and sensorless vector control. It seems to me either would be fine. Although I think I would have more torque at lower RPM's with the sensorless vector.

Additionally I wonder if the sensorless vector versions would provide better effeciency and/or longevity? Also (since I have never put my hands on a VFD) Do I need additional parts? Is there a speed knob on all versions? If not, does the keypad allow for control? Are they reversible? In my application, are there any other features / settings / controls I should consider?

If possible, I would appreciate suggestions on models or versions.

Thanks!
Darren

Hi Darren, welcome to the forum. Sorry for not seeing this earlier, it slipped past my "View New Posts" link.

Vector control will give you better performance at lower speeds, say 15Hz and below. If you plan to use it a lot there for precision work, then go for the vector drive. If the only thing you do at low speed is something like polishing, then it doesn't matter. But most small drives with 120V input now are sensorless vector capable anyway. If you find a deal on one that is not, it's probably a surplus of a discontinued model, something to think about.

Efficiency will not be any better, no advantage there. But I wouldn't worry too much about efficiency anyway. On a VFD, when you turn down the speed, that's where the efficiency drops off. But also, when you turn down the speed the HP drops off too. So your wasted energy is a higher percentage of a much lower amount to begin with, making it almost irrelevant.

Speed knobs built-in varies from manufacturer to manufacturer so there is no way to tell without looking. Keypads will always allow for speed control.

All VFDs are inherently capable of reversing. For them, it's just a function of what they tell the transistors to do.

Other considerations:
Changing speed with a VFD is not the same as changing speed with belts and pulleys. In a belted system, lowering the work speed INCREASES the torque by the same ratio. With a VFD, the torque remains constant. If your work requires more torque at lower speeds, you may have to use a higher HP motor and a VFD. I usually recommend that users leave the pulley system in place just in case. The VFD is then used to make speed changes easier, but the pulleys are there if you need them.

You might also consider braking as an option, but on a lathe, it depends. Wood or metal lathe? If it's a wood lathe and you are going to do work on the hub only, like a bowl, then you do NOT want braking. If you brake, the hub unscrews itself and your work piece goes flying, usually right at you! But if it's a metal lathe and you want to do threading, braking is almost essential.

Brands? One that is available from a local supplier that you trust. If you need help, most of the lowest-price internet outfits have very poor support. They give you an 800 number, but nobody answers it. But in general, anyone who went to the extreme expense to develop a small VFD and produce them in quantities large enough to be competitive, makes a pretty good product, otherwise they would be out of business quickly. So it's hard to go wrong. But a trick is, get a manual from them in advance and see if it makes sense to you. Some Asian mfrs are terrible at translating manuals and that can make your life difficult.

Good luck, I think you will enjoy it.

Hi! this is sethu here...

this si good concept.

can i say if am working with 50Hz and 2980rpm ans power is 1kW

if i go up to 12.5Hz and 750rpm my power requireent is still 1kW

so the motor i should select is 4kW