Single phase, 3-phase, VFDs, RPCs, and DPCs... time for some schoolin'

OK for fun: a 100 plus year old rotary converter for the old NYC subway - it's amazing...

 
Dabbler said:
One of my friends VFD'd his 7.5 HP lathe, and modified the entire control package to make it seamless. A lot of costly work, but he likes it a lot.

A bit of food for thought: It it were just a mill and lathe, with the usual controls, well, you can get away with either approach. You could do 2 VFDs as most mills are 3HP or less, and that lathe in 3 phase 2 HP or less. this is in the inexpensive range for a pair of VFDs. That said, it is a smallish increment to go to a 5HP RPC which would do both machines, and if you order your lathe in 3PH, no additional costly wiring.

Another friend bought a GV1440 in single phase, and within the year wired it for 3PH. it took him a week of full days.

I think that @strantor and @mksj are spot on. Perhaps get the smart rotary phase converter. If you later need speed control, you can convert the lathe to VFD later...
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Eventually, I might add a surface grinder to that list. An air-compressor could be 3-phase, but air-compressors are readily available in single phase. I don't know of any other equipment that would need 3-phase. A horizontal mill is appealing, but I doubt I would buy one unless I came a cross a real bargain. Eventually, I would like a CNC machine, probably to make as a project, probably based on the 940V, but that is a single phase machine.

Leaning towards the scary (for me) VFD route at the moment...
 
ArmyDoc said:
An air-compressor could be 3-phase, but air-compressors are readily available in single phase. [...]
Leaning towards the scary (for me) VFD route at the moment...
Click to expand...
I know you're drinking from a fire hose right now, but you seem to be getting it all, otherwise I wouldn't mention what I'm about to. Since you are leaning toward VFDs, let me provide an example of the doors a VFD can open for you if you like to tinker. Here is the thread about my 3HP VFD/3PH powered compressor. I get the performance of a 7.5HP compressor from it at some points in the operation.

That's an atypical example, but the more common examples of the beneficial aspects of VFD are:

DC braking: the VFD can ramp the speed of a spinning motor down much faster than it would decelerate if you simply removed power with a switch. This saves you time, especially on the lathe. Coming to a stop faster than you can grab a micrometer is very nice. This can be accomplished to a limited extent with just a VFD, but in order to achieve dramatic stops you'll need a braking resistor. Dramatic stops may be undesirable with a threaded lathe chuck. Keep in mind this option is available for any VFD setup, not just lathe spindles.

(Obvious) Adjustable speed: mechanical speed ranges can be made obsolete in most/many applications. This is especially nice when those speed ranges are achieved by belt/pulley changes. I removed all the belts and stepped pulleys, intermediate shafts and such from my lathe. I have a single belt going from my motor to my spindle. I can change my speed on the fly by turning a dial. Very nice. There is a tradeoff however; with a mechanical speed reduction comes a proportional increased in available torque. With a VFD/motor speed change there is not. I removed a 1/2HP single phase motor and replaced it with a 1.5HP 3 phase motor, and rarely have a situation where I can't hit the desired speed/cutting load. This on-the-fly speed adjustment allows me to face large parts while maintaining a more-or-less constant surface speed for a nice finish which would be impossible if stopping for belt changes.

Warp speed: you can go faster than 60Hz. This comes in handy when drilling with small bits. As long as your spindle can cope with it, most inverter duty motors are safe to operate up to double the nameplate RPM (see motor MFG documentation, usually a "maximum safe speed" spec will be given)

Motor & machine protection: Many older & smaller machines (the type hobbyists usually end up with) do not come with any sort of overload protection. At least the ones I've seen haven't. Without this, if a motor gets overloaded or if a 3 phase motor gets single phased, you're likely to burn up a motor or mechanically damage your machine. The VFD will fault out in this scenario, saving your motor and maybe your machine (and shop, if fire would have otherwise resulted).

Power factor improvement: not typically a concern for hobbyists, but it can become one. A large AC motor doing much less work than it is designed for, has a horrible power factor. This can draw the attention of your utility company and result in high charges. I had a 3-month span last year where my utility company was absolutely raping me on my power bill. My kW usage was not much higher than normal, and my cents/kW was the same as it always had been, but the ambiguous line item "TDU charges" was 3x-5x what it would be typically. The "TDU charges" were higher than the charges for my kW usage. I spent many cumulative hours on the phone trying to find out what was up, never got any answer, but eventually my bills went back to normal. I suspect it was the result of running of my 30HP RPC continually for prolonged periods. I was commissioning a large conveyor panel that required 480V 3ph but barely drew any power most of the time, so i just left that RPC spinning 24/7 for a while and I think it got me put on a naughty list somewhere. A VFD has effectively as close to "perfect" power factor as possible, so you won't need to worry about this.

Hour meters: I don't know if many hobbyists track runtime and do scheduled preventive maintenance, but if wanted to, that VFD is keeping track of your runtime hours.

Inputs & outputs: VFDs typically have several digital inputs and outputs, including relay outputs and often including analog outputs. These become invaluable if you decide that you want to add functionality to your machine. For example if you want to add a carriage stop to a lathe that doesn't have a VFD, usually this would require some creative mechanical solution. With a VFD you can just mount an adjustable limit switch or proximity sensor and wire it to the VFD's enable terminal. You could wire lights to the VFD to indicate when the motor is in its commanded speed range (to indicate cutting load too high), or you could wire an analog or LCD meter to an analog output to provide feedback on cutting load. You could wire a coolant pump to an output so that it automatically turns on if the spindle is running. I could continue providing examples, but the possibilities are endless. If you want to "pimp your ride," a VFD is how you do it.

Ok I've already typed more than anyone else would read and I have people waiting to use the bathroom so I'm ending this here. Sorry for the long post. I got carried away.
 
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strantor said:
I know you're drinking from a fire hose right now, but you seem to be getting it all, otherwise I wouldn't mention what I'm about to. Since you are leaning toward VFDs, let me provide an example of the doors a VFD can open for you if you like to tinker. Here is the thread about my 3HP VFD/3PH powered compressor. I get the performance of a 7.5HP compressor from it at some points in the operation.

That's an atypical example, but the more common examples of the beneficial aspects of VFD are:

DC braking: the VFD can ramp the speed of a spinning motor down much faster than it would decelerate if you simply removed power with a switch. This saves you time, especially on the lathe. Coming to a stop faster than you can grab a micrometer is very nice. This can be accomplished to a limited extent with just a VFD, but in order to achieve dramatic stops you'll need a braking resistor. Dramatic stops may be undesirable with a threaded lathe chuck. Keep in mind this option is available for any VFD setup, not just lathe spindles.

(Obvious) Adjustable speed: mechanical speed ranges can be made obsolete in most/many applications. This is especially nice when those speed ranges are achieved by belt/pulley changes. I removed all the belts and stepped pulleys, intermediate shafts and such from my lathe. I have a single belt going from my motor to my spindle. I can change my speed on the fly by turning a dial. Very nice. There is a tradeoff however; with a mechanical speed reduction comes a proportional increased in available torque. With a VFD/motor speed change there is not. I removed a 1/2HP single phase motor and replaced it with a 1.5HP 3 phase motor, and rarely have a situation where I can't hit the desired speed/cutting load. This on-the-fly speed adjustment allows me to face large parts while maintaining a more-or-less constant surface speed for a nice finish which would be impossible if stopping for belt changes.

Warp speed: you can go faster than 60Hz. This comes in handy when drilling with small bits. As long as your spindle can cope with it, most inverter duty motors are safe to operate up to double the nameplate RPM (see motor MFG documentation, usually a "maximum safe speed" spec will be given)

Motor & machine protection: Many older & smaller machines (the type hobbyists usually end up with) do not come with any sort of overload protection. At least the ones I've seen haven't. Without this, if a motor gets overloaded or if a 3 phase motor gets single phased, you're likely to burn up a motor or mechanically damage your machine. The VFD will fault out in this scenario, saving your motor and maybe your machine (and shop, if fire would have otherwise resulted).

Power factor improvement: not typically a concern for hobbyists, but it can become one. A large AC motor doing much less work than it is designed for, has a horrible power factor. This can draw the attention of your utility company and result in high charges. I had a 3-month span last year where my utility company was absolutely raping me on my power bill. My kW usage was not much higher than normal, and my cents/kW was the same as it always had been, but the ambiguous line item "TDU charges" was 3x-5x what it would be typically. The "TDU charges" were higher than the charges for my kW usage. I spent many cumulative hours on the phone trying to find out what was up, never got any answer, but eventually my bills went back to normal. I suspect it was the result of running of my 30HP RPC continually for prolonged periods. I was commissioning a large conveyor panel that required 480V 3ph but barely drew any power most of the time, so i just left that RPC spinning 24/7 for a while and I think it got me put on a naughty list somewhere. A VFD has effectively as close to "perfect" power factor as possible, so you won't need to worry about this.

Hour meters: I don't know if many hobbyists track runtime and do scheduled preventive maintenance, but if wanted to, that VFD is keeping track of your runtime hours.

Inputs & outputs: VFDs typically have several digital inputs and outputs, including relay outputs and often including analog outputs. These become invaluable if you decide that you want to add functionality to your machine. For example if you want to add a carriage stop to a lathe that doesn't have a VFD, usually this would require some creative mechanical solution. With a VFD you can just mount an adjustable limit switch or proximity sensor and wire it to the VFD's enable terminal. You could wire lights to the VFD to indicate when the motor is in its commanded speed range (to indicate cutting load too high), or you could wire an analog or LCD meter to an analog output to provide feedback on cutting load. You could wire a coolant pump to an output so that it automatically turns on if the spindle is running. I could continue providing examples, but the possibilities are endless. If you want to "pimp your ride," a VFD is how you do it.

Ok I've already typed more than anyone else would read and I have people waiting to use the bathroom so I'm ending this here. Sorry for the long post. I got carried away.
Click to expand...

That sounds cool.
 
I am also using a static phase convertor. I bought it as a make-do solution until I received my 7.5 hp RPC. After using the RPC for a couple of months, I got tired of the whine (and my wife got a look at the electric bill). I decommissioned it and reverted to using the SPC. I have one of the SPCs that can be configured for 3/4 - 5 hp motors. My mill is 2 hp and my lathe is 1 hp. Instead of changing the settings on the SPC when switching machines, I leave it set for 2 hp. When I want to use the lathe I turn on the mill and let it function as an RPC. I have not had any sort of problems with surface finish or machine power. I have no plans or desire to switch to another system.
 
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