etpm
Veteran Member
This one looks like it would work for you. 4.5KW 6HP VFD Driver Inverter 1phase AC220V 21A 1000Hz Spindle Motor Controller 712640469078 | eBay
It says it has automatic current sensing. $259. VFDs have come a long way since I last shopped for one 3 years ago. You still may need to program this for each motor but I don't know. What ponytug posted is true, especially about older motors and VFDs. Because of the way they work, especially the less expensive ones, voltage spikes can be quite high and they might cause arcing inside the motor. When a motor is operated in a high humidity environment arcing in older motors is more common. Motors running on VFDs also tend to run a little warmer. A VFD chops up the power into square waves so the output must be smoothed out with capacitors so that it approximates a sine wave. The sorta sine wave output from cheaper units is really composed of a bunch of steps which are smoothed somewhat so that they are not quite square but are also not a smooth sine wave. This can cause the motor to run much warmer. I, personally, have had good luck with inexpensive VFDs running older motors. Some folks don't. And they are better these days. Though a Rotary Phase Converter does not deliver perfect 3 phase power it will, when properly balanced with capacitors, do a good job for pretty cheap. I use one in my shop to power CNC machines. One machine has a FANUC brand control and these controls are notorious for needing clean 3 phase power and will shut themselves off if the power isn't good enough. Through the years I have had for machines with FANUC controls running off my big RPC and they have never had a problem because my RPC is well balanced. You don't need one that well balanced and so it would be an easy build. Interestingly, you can use a smaller RPC, power a couple machines with it, and as long as they are running a third, more powerful machine can be started and run. This is because the motors already running will act as generators to help the new motor to start. There are limits to this scheme because the voltage will become more unbalanced and the wiring will need to be able to handle the current. If you had a 7 or 7.5 hp 3 phase motor you could even probably get away with a rope start RPC.
Eric
It says it has automatic current sensing. $259. VFDs have come a long way since I last shopped for one 3 years ago. You still may need to program this for each motor but I don't know. What ponytug posted is true, especially about older motors and VFDs. Because of the way they work, especially the less expensive ones, voltage spikes can be quite high and they might cause arcing inside the motor. When a motor is operated in a high humidity environment arcing in older motors is more common. Motors running on VFDs also tend to run a little warmer. A VFD chops up the power into square waves so the output must be smoothed out with capacitors so that it approximates a sine wave. The sorta sine wave output from cheaper units is really composed of a bunch of steps which are smoothed somewhat so that they are not quite square but are also not a smooth sine wave. This can cause the motor to run much warmer. I, personally, have had good luck with inexpensive VFDs running older motors. Some folks don't. And they are better these days. Though a Rotary Phase Converter does not deliver perfect 3 phase power it will, when properly balanced with capacitors, do a good job for pretty cheap. I use one in my shop to power CNC machines. One machine has a FANUC brand control and these controls are notorious for needing clean 3 phase power and will shut themselves off if the power isn't good enough. Through the years I have had for machines with FANUC controls running off my big RPC and they have never had a problem because my RPC is well balanced. You don't need one that well balanced and so it would be an easy build. Interestingly, you can use a smaller RPC, power a couple machines with it, and as long as they are running a third, more powerful machine can be started and run. This is because the motors already running will act as generators to help the new motor to start. There are limits to this scheme because the voltage will become more unbalanced and the wiring will need to be able to handle the current. If you had a 7 or 7.5 hp 3 phase motor you could even probably get away with a rope start RPC.
Eric