3 phase for a tool with 2 motors

[Dabbler]

@projectnut The manufacturer might be working from an abundance of caution. VFDs and SPCs can develop elevated voltages and/or abrupt leading edges in the waveform. If the insulation is very old, or made of materials like shellac, there is a possibility that this can lead to breakdown, resulting in arcing in the motor.

Well made motors and better quality SPCs can help minimize these concerns.

 

[Shotgun]

I don't understand the draw of an SPC for 2Hp or less motors in 2023. They cost as much as a VFD, and you lose 1/3rd to 1/2 of the motor power. Setting up the cheap VFDs to use them as a motor control can be a PIA, especially if you haven't done it before. But, setting them up as a simple 2 to 3-phase converter is on the lower end of the difficulty scale of the things we do.

 

[projectnut]

I don't understand the draw of an SPC for 2Hp or less motors in 2023. They cost as much as a VFD, and you lose 1/3rd to 1/2 of the motor power. Setting up the cheap VFDs to use them as a motor control can be a PIA, especially if you haven't done it before. But, setting them up as a simple 2 to 3-phase converter is on the lower end of the difficulty scale of the things we do.

They may not be as cost effective as they were when I was buying them. All of the SPC's I purchased were used on 1/3 to 2 hp motors. At the time the smallest one was less than $40.00 and the larger ones were less than $60.00. The upside is that there is virtually no wiring on the machine that needs to be changed. That's why I chose them.

I wanted to use the original control stations on the mill and lathe. Both have variable speed spindles so there is no need to dial in a frequency change. Just push the existing speed control buttons or change speed by turning the crank. Motor torque remains the same at any spindle speed. You will lose about 1/3 the rated hp, but in over 20 years of using one on the mill and 8 years on the lathe there have never been any problems. I mill and turn some large and difficult material from time to time and have never had problems with machines over heating or lack of power.

I do have a VFD on my Baileigh cold saw. It has a 3hp 3 phase motor that's powered through a Delta E series VFD. The VFD was incorporated in the machine from the factory. As such I can plug it into any 220V single phase outlet and still use the original control station.

 

[Larry$]

He also cautioned me on using them on older than '64 motors.

I think the issue with some older motors is not enough "reserve heat dissipation capacity" to be run @ full load on a converter. Phase converters of most types won't provide balanced 3 phase so the motors will not be able to make full load power. I don't remember what % (85%??) In the case of a mill or lathe in hobby use it is highly unlikely you will ever run at full load, let alone for any extended time enough to over heat. A compressor might be a different deal.

I ran my quite old Maka morticer on my home built RPC for years. YMMV

 

[PNW_Guy]

I'm not sure I buy into the not using SPC's on motors older than 1964. I have one on my 1960 Sheldon lathe and another on my late 1950's era Racine power hacksaw. I've had both machines for over 8 years. The lathe has run as much as 50 hours a week, and the saw has run as much as 20 hours a week. The saw is used far less than the lathe, but the lathe is normally being run 10 hours a week or more. The motors always seen to run cool, quiet, and have plenty of power.

His reasoning for not using them on older motors has to do with not actually providing a 3rd leg after startup. I don't know what happened post '64, but if the tech who works for NAPC is warning me about using his product in my situation, I'm going to defer to the expert.

 

[MrWhoopee]

My SB Heavy 10 is a 1963 with a 1hp motor. The SPC I bought is adjustable for different hp. I was never able to make them happy together, the SPC would not disengage the third leg after the motor started, which can be quickly fatal for the SPC.
I fail to see why the OP was told he needed 2 SPCs, though I don't know the specifics. Once the first motor has started, it functions as an RPC. When I start my lathe (with the mill functioning as an RPC), the SPC does not engage. I have tried turning off the mill once the lathe is started, there is a very noticeable drop in power. The mill is perfectly happy running on 2 legs, the lathe is not.

 

[projectnut]

His reasoning for not using them on older motors has to do with not actually providing a 3rd leg after startup. I don't know what happened post '64, but if the tech who works for NAPC is warning me about using his product in my situation, I'm going to defer to the expert.

I would ask for a second experts opinion,and also ask if the SPCs have changed in design since 2016. I explained to the NAPC rep in detail what the converters were being used for as well as the age and hp of each machine. At that time there were no cautions expressed as to what age or hp of the machines they could be used on. They did caution against using them on certain kinds of machines like compressors, welders, CNC machines and some others

 

[Larry$]

not actually providing a 3rd leg after startup.

No 3rd leg?? So a SPC is just a way of kicking a 3 phase motor over to spin fast enough to run on two legs?? If that's the case just get yourself some big electrolytic caps (& a couple of bleed resistors) for your lathe/mill/??
I'm missing something about calling a SPC a converter, if all it is is a means of kicking a motor up to the speed it will run on single phase 220

 

[MrWhoopee]

No 3rd leg?? So a SPC is just a way of kicking a 3 phase motor over to spin fast enough to run on two legs?? If that's the case just get yourself some big electrolytic caps (& a couple of bleed resistors) for your lathe/mill/??
I'm missing something about calling a SPC a converter, if all it is is a means of kicking a motor up to the speed it will run on single phase 220

That is correct, once the motor has started the SPC drops out completely and the motor runs on 2 legs. An SPC is more correctly a motor starter, it's only a converter momentarily. They can be combined with a motor to build an RPC.

 

[PNW_Guy]

No 3rd leg?? So a SPC is just a way of kicking a 3 phase motor over to spin fast enough to run on two legs?? If that's the case just get yourself some big electrolytic caps (& a couple of bleed resistors) for your lathe/mill/??
I'm missing something about calling a SPC a converter, if all it is is a means of kicking a motor up to the speed it will run on single phase 220

Correct - there are two hot legs going from the 240v plug to two legs of the motor, as well as a cap. The cap(s) are used to start the motor, which then runs on 2 legs at 180*, rather than 3 legs at 120*.

It's called a Static converter in the industry.

I'm not going to build one. This is for a buddy's mill, and I'm helping with the research. He's welcome to build or buy whatever he wants.