Electrical question - 3 phase to 1 phase

[Joe Melton]

I found a deal I couldn't refuse on a Delta 31-730 sander. It is a combination 6x48" belt and 12" disk sander. The machine came with a 1.5hp 3-phase motor and, not having 3-phase service, I want to convert it to 220V single phase. I have a 5hp air compressor motor that will fit.
I'm wondering if I can use the same on/off switch.
The sander has an attached 52-702 magnetic motor starter that is part of the 3-phase setup, I guess. Consequently, the wires to the switch, in that they come from the starter rather than the motor, are smaller guage than those used with the single-phase motor.
The switch has two wires to both the start and stop buttons.
Any advice is appreciated.
Joe

[Cliff Rohrabacher]

I'd use the switch that is being used normally for the single phase motor and skip the Mag switch bit entirely.

Mag switches are not direct. They are lower voltage switches that throw a relay from which the operator is shielded. That relay throws the high current on and off.

The three phase mag switch isn't made for single phase operation being part of a relay switch that throws three hot wires at once.

I suppose you might be able to figure out how to make it throw just the one hot for a 220 line depending on how you wire it. It just seems like a lot of bother to me.

[Kyle Kraft]

Can't you just use 2 of the 3 poles on the starter? As long as the coil or the control transformer voltage is appropriate, the mag doesn't know how many wires are hooked to the contactor portion.

[M Toupin]

Joe,
Yes, you can use the 3 ph mag starter, and I'd recommend you do. All you have to do is use two legs instead of 3. Check out the electrical section of the OWWM.com wilki which covers exactly what you're trying to do. http://wiki.owwm.com/ow.asp?MotorStarterWiringDiagrams

Mike

[Rick Christopherson]

I'm not too keen on the idea of putting a 5 hp motor in a chassis designed for 1.5 hp. However, now that I have said that, I am wondering about the validity of that actually being a 5 hp motor. If the compressor is the kind that plugged into a 120 volt outlet, then ignore the above comment, because it is just a 1.5 hp motor then.

Personally, I would keep the 3-phase motor and use a VFD to power it. This is a perfect application for a VFD because it would allow you to slow down the sander. These combination sanders are really made for metal work, so they will frequently burn the wood. By slowing the sander down at times, you can control this burning. The 2-hp FM50 from FactoryMation is $145, and this would give you a really cool sander.

[Kyle Kraft]

Rick,
I would take the 5hp rating of the compressor motor with grain of salt. This being said as the handyman compressor folks grossly overstate the hp of their machines. The best bet is use good ol' Ohm's law to determine the "real" hp of the motor in question. Volts x amps = watts. 746 watts = 1 hp; at least for the sake of our discussion. I'm just a tad bit leery of a compressor motor with a mfgrs 5 hp sticker on it when the motor nameplate says it draws 15 amps @ 120V.

[Rick Christopherson]

I wanted to update my posting after getting a PM from the original poster that sparked my memory. At the time I made my posting, I hadn't realized that a GS1 VFD from Automation Direct is only $10 more than the TECO FM50. For the $10 difference, getting a GS1 is a no-brainer versus the FM50, which is not as advanced.


The GS1 (and its bigger brother, the GS2) are my preferred VFDs for their functionality at a low cost, but for some reason, I was thinking that the GS1 was significantly more expensive than the FM50, so I didn't mention it until now.

[Rod Sheridan]

Many small air compressor motors are labled SP or Compressor Duty.

This indicates that they aren't rated for continuous duty, since the compressor is designed to have a duty cycle. (Run periods with time off periods).

A sander may be required to run continuously, in addition to the problem with dust getting into the motor.

The dust will reduce the cooling ability of the motor, which may be marginal to begin with if it's a duty cycle motor. The single phase motor will also have a starting switch, whose arcing could ignite dust in the motor.

As for using your 3 pole starter for the single phase motor, the starter probably won't have enough current capacity, and the overload relay if not adjustable to the correct value will require replacing.

The starter will have a horsepower rating marked on it for different supply voltages, and single and three phase values. Check to make sure the starter is rated at 5 HP at 240 Volts single phase if you wish to use it.

Reards, Rod.

[CPeter James]

It would seem that the VFD would be the ideal answer as you could control the speed of the sander, both up and down. Cheaper, easier and an improvement over original.

CPeter

[Joe Melton]

I found a nice 1.5hp Baldor motor and am fitting it to the sander, using the 230V option. I plan to hook the two hots to the motor to T1 and T2, and the two hots on the incoming line to L1 and L2. The hots from the three-phase motor went to T1, T2 and T3.
The problem is what to do with the commons. The diagram on the OWW site doesn't show that, or it does and I don't understand it.
The Baldor motor diagram has a single white wire labeled "J". Is that electrical parlance for "common"? If so, I can just connect that directly to the incoming common, right?
Thanks,
Joe