Lathe in residential garage

[sii]

I have a customer who has purchased a lathe for his garage, a 3-phase, 220 volt, 7.5 hp Summit. It shows 7.5/6.1 FLA on the name plate. I haven't seen it but he said it was made in the late 70's and has a pretty complicated control system. He also has purchased a Phase-A-Matic phase converter; 4-8 hp, 22 FLA on the primary side.

I have never wired a phase converter but my first thought, without seeing any of this equipment is that it has to go between the contactor and the motor; it cannot feed the entire lathe since the control voltage is derived from the mains. He did say that only the big motor runs on three phase, the coolant pump has it's own single phase cord and plug. Am I on the thinking correctly.

Secondly, there is only one 20 amp circuit serving the garage so obviously that has to be upgraded. It is approximately 30' from the 150 amp house panel to the location in the garage where the new panel would be located. Plenty of spaces available in the house. I would like to put a 100 amp, 8 space loadcenter in the garage or maybe slightly smaller.

The lathe runs off of a clutch and he says that the motor starts unloaded. Should I be concerned about "browning out" the house when that lathe starts?

Any other thoughts would be welcome as well, especially concerning the phase converter. TIA

 

[LarryFine]

In no particular order:

A. The difference in cost of a 60A feeder and a 100a feeder isn't enough to scrimp.

2. Make sure the motor can be separately supplied from the rest of the machine.

D. Make sure you continue the two line conductors to any 1ph loads within it.

 

[sii]

2. Make sure the motor can be separately supplied from the rest of the machine.

I think that the big motor is the only three phase load and that he is planning on reworking the entire control system to run on single phase. We haven't talked about that much because the lathe is not in a location where I can lay eyes on it and there is no diagram. That part is moot until we can get power out there anyway.

No concern about the inrush of the motor causing problems in the house?

 

[Jraef]

A VFD would have been a better choice than the Phase-A-Matic unit in my opinion. It would create the 3 phase for the motor without a loss of HP (the static Phase-A-Matics cost you 25% of the motor rated power), do the reversing electronically and soft start, plus he gets the added benefit of infinitely variable speed. If it's not too late, see if he can return the Phase-A-Matic.

If not, make sure it can handle being down stream of a reversing contactor. Assuming it's a static converter, they sell two kinds, regular and heavy duty. They will recommend the regular model if the lathe has a clutch, but if he wants to instantly reverse, i.e. tapping or thread cutting, then he needed to have bought the heavy duty version.

By the way, don't forget that the motor FLA on the nameplate is the 3 phase rating. If you supply it from a 1 phase source, the current draw from the source increases by a factor of 1.732. So your 7.5A becomes 13A

 

[hurk27]

With a phase-O-Matic you can also add a fly wheel motor to it to get full power on the lath, and it will handle instant reverses. but adding the fly wheel motor will be as costly as buying a VFD or a roto phase converter.

 

[sii]

I guess I've never seen a VFD that big that can handle single phase input. The biggest I've ever seen was I think 3 hp.

 

[Jraef]

I guess I've never seen a VFD that big that can handle single phase input. The biggest I've ever seen was I think 3 hp.

Most VFDs can be used for 1 phase input, but you must double the size of the VFD to account for the higher input current through the rectifier and the added ripple on the DC bus (more capacitance). There are a few that have built-in phase loss protection, and a few of those do not allow you to disable that function, making them unsuitable. but not many are like that.

 

[sii]

Most VFDs can be used for 1 phase input, but you must double the size of the VFD to account for the higher input current through the rectifier and the added ripple on the DC bus (more capacitance). There are a few that have built-in phase loss protection, and a few of those do not allow you to disable that function, making them unsuitable. but not many are like that.

I guess I often forget that but I'm pretty sure I can't get that done for less than $1000. I don't think I can sell that to the guy.