I am adding a new to me lathe in my shop. Its a Mazak with a 10 HP, 3 phase motor. I have used static phase converters, rotary phase converters and VFD’s in the past. I really like the utility of a VFD. But, when the electrical panel looks like this I question the viability of inserting the VFD so that it is directly connected to the motor. I also wonder about my ability to get in and out of 40 year old wiring without causing additional problems. This may just be a case where a rotary phase converter is the better option. I’m going to ponder on it over the weekend and was curious if anyone else had thought through this before.
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Rethinking My Approach with a VFD
- Thread starter TNBen60
- Start date
I have installed several VFDs (none in a system like this). In my opinion, if you want to keep the existing controls, a rotary phase converter is a better choice as it can supply 3 phase to the existing controls which would be a poor choice for a VFD.
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Yeah, probably a better candidate for an RPC.
Do all the controls work properly as it sits? Does it have the required speeds for the work you'll be doing?
I love the VFD's on my lathes but they are older models without too much in the way of electrical in the first place (the Seneca Falls didn't even come to me with a switch). For a modern lathe (assuming CNC) it probably doesn't make sense to rewire it unless there are major issues with the controls to begin with.
@mksj would be the go to person for a real answer though.
John
Do all the controls work properly as it sits? Does it have the required speeds for the work you'll be doing?
I love the VFD's on my lathes but they are older models without too much in the way of electrical in the first place (the Seneca Falls didn't even come to me with a switch). For a modern lathe (assuming CNC) it probably doesn't make sense to rewire it unless there are major issues with the controls to begin with.
@mksj would be the go to person for a real answer though.
John
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I have some (indirect) experience with this: a friend of mine rewired his lathe for a VFD/3PH motor from a single phase motor. It tok him about a full-time week to get it done, and he has some experience with wiring.
RPC is your best bet, even if pricier. You need to upsize your RPC because of the large starting mass of a lathe. I use a 15HP RPC for a 7.5 HP lathe. The manufacturers suggest 30% higher, but I prefer to have some 'breathing room'
RPC is your best bet, even if pricier. You need to upsize your RPC because of the large starting mass of a lathe. I use a 15HP RPC for a 7.5 HP lathe. The manufacturers suggest 30% higher, but I prefer to have some 'breathing room'
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I went a different direction with my lathe because the lathe has a two-speed motor and I didn't want to deal with it. I have a VFD that accepts single-phase input and can be set to output 240 VAC, 60Hz all of the time. I wired in a sine-wave filter to its output and I have the equivalent of a rotary phase converter without all the spinning. Typically to use most VFDs you should have about 1.5X the three-phase output rating. My VFD is 200 Amp rated 
... so no problem. When I'm feeling jiggy I up the frequency to 66 Hz. for a little more speed.
I do want to revisit a real VFD for the lathe at some point but I don't know if it will really happen. Maybe I'll do it when I get to the ELS project I've not gotten around to either.
... so no problem. When I'm feeling jiggy I up the frequency to 66 Hz. for a little more speed.I do want to revisit a real VFD for the lathe at some point but I don't know if it will really happen. Maybe I'll do it when I get to the ELS project I've not gotten around to either.
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For 10 HP I would go with a RPC. Up to 5HP a VFD with a single phase input works OK. If you want a variable speed spindle, then a RPC feeding a VFD would be my choice. This is how I run my 10 HP spindle lathe.
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Or a Phase Perfect, especially for you are running any other machines like CNC's that the circuit boards are a lot of money to replace or repair. I use the a Phase perfect for multiple machines like a 3 phase per supply for the shop.
You intrigue me and this is was why I posted this. If you don’t mind I will pepper you with a few questions.I went a different direction with my lathe because the lathe has a two-speed motor and I didn't want to deal with it. I have a VFD that accepts single-phase input and can be set to output 240 VAC, 60Hz all of the time. I wired in a sine-wave filter to its output and I have the equivalent of a rotary phase converter without all the spinning. Typically to use most VFDs you should have about 1.5X the three-phase output rating. My VFD is 200 Amp rated
I do want to revisit a real VFD for the lathe at some point but I don't know if it will really happen. Maybe I'll do it when I get to the ELS project I've not gotten around to either.
1.) Do I understand correctly that the VFD runs continuously. You then power the lathe with a magnetic switch and use it’s controls normally?
2.) How do you get the VFD to power up without the motor load without complaining?
3.) Tell me about this sine wave filter of which you speak?
Like you I have no intention of varying the output frequency as there are more speeds in the gears than I know what to do with.
Thanks
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Phase Perfect generates the third leg and passes through the the two single phase lines. It also filters the generated leg so it is very close to a sine wave, and it is not effected by the load. It is not a variable speed VFD, it is designed to provide fixed 60Hz 3 phase power from single phase. There have been issues with reflected electrical noise into the input line, I believe this is an issue with the older models. It has a very high efficiency (98.7) vs. say and RPC, so can be left on continuously, and newer models appear to have less physical noise than the older models. Downside is cost, but if you have multiple larger 3 phase machines then the investment may be worth it. They are rated to their specified output Hp/amps and are the output (all legs) are compatible with electrical control systems, multiple motors, etc.
www.phaseperfect.com
If you wanted variable speed, you could add a VFD, it would need to be oversized for single phase use, and you are pretty much looking at a complete new control system. I have done those for different individuals, but a lot of factors to consider and not a simple process. When all is said and done you are probably getting close to the cost of a Phase Perfect. You also need to figure in the ancillary costs and power source for any of the choices, as well as electrical code requirements. It has also come up that there can be issues with power companies if you are pulling large current draws that can pull down the line voltage of surrounding neighbors.
Phase Technologies
www.phaseperfect.com
If you wanted variable speed, you could add a VFD, it would need to be oversized for single phase use, and you are pretty much looking at a complete new control system. I have done those for different individuals, but a lot of factors to consider and not a simple process. When all is said and done you are probably getting close to the cost of a Phase Perfect. You also need to figure in the ancillary costs and power source for any of the choices, as well as electrical code requirements. It has also come up that there can be issues with power companies if you are pulling large current draws that can pull down the line voltage of surrounding neighbors.
Phase Perfect generates the third leg and passes through the the two single phase lines. It also filters the generated leg so it is very close to a sine wave, and it is not effected by the load. It is not a variable speed VFD, it is designed to provide fixed 60Hz 3 phase power from single phase. There have been issues with reflected electrical noise into the input line, I believe this is an issue with the older models. It has a very high efficiency (98.7) vs. say and RPC, so can be left on continuously, and newer models appear to have less physical noise than the older models. Downside is cost, but if you have multiple larger 3 phase machines then the investment may be worth it. They are rated to their specified output Hp/amps and are the output (all legs) are compatible with electrical control systems, multiple motors, etc.
Phase Technologies
If you wanted variable speed, you could add a VFD, it would need to be oversized for single phase use, and you are pretty much looking at a complete new control system. I have done those for different individuals, but a lot of factors to consider and not a simple process. When all is said and done you are probably getting close to the cost of a Phase Perfect. You also need to figure in the ancillary costs and power source for any of the choices, as well as electrical code requirements. It has also come up that there can be issues with power companies if you are pulling large current draws that can pull down the line voltage of surrounding neighbors.
I really appreciate the information. I had a thought that I might have to place the shop light switch near the lathe. That way I could turn the lights out, start the lathe, then turn the lights back on. Don’t want to overload anything you know.Phase Perfect generates the third leg and passes through the the two single phase lines. It also filters the generated leg so it is very close to a sine wave, and it is not effected by the load. It is not a variable speed VFD, it is designed to provide fixed 60Hz 3 phase power from single phase. There have been issues with reflected electrical noise into the input line, I believe this is an issue with the older models. It has a very high efficiency (98.7) vs. say and RPC, so can be left on continuously, and newer models appear to have less physical noise than the older models. Downside is cost, but if you have multiple larger 3 phase machines then the investment may be worth it. They are rated to their specified output Hp/amps and are the output (all legs) are compatible with electrical control systems, multiple motors, etc.
Phase Technologies
If you wanted variable speed, you could add a VFD, it would need to be oversized for single phase use, and you are pretty much looking at a complete new control system. I have done those for different individuals, but a lot of factors to consider and not a simple process. When all is said and done you are probably getting close to the cost of a Phase Perfect. You also need to figure in the ancillary costs and power source for any of the choices, as well as electrical code requirements. It has also come up that there can be issues with power companies if you are pulling large current draws that can pull down the line voltage of surrounding neighbors.