Planning for 3 phase in new shop, newb question

[philshevlin]

I'm about to break ground on a new shop. I plan to run 90-100 amps to it. As it stands right now I will only be running a few single phase 220 tools (welder, compressor, etc.)

However, now that I am going to finally have a shop, I want to have the capability to run 3 phase tools.

I'm ignorant when it comes to wiring. I know a converter is what I'll need.

But should I be doing anything now -- in preparation?

Thanks.
Phil

 

[ron in sc]

Call your power company and see if 3 phase is available where you want it.

 

[philshevlin]

Its not feasible for me to run a new meter to the shop. Its considered "commercial" if I do that. So, I'm stuck running 100 amp MHF out to the building.

 

[md21722]

3 phase in a home shop is best for small motors where a VFD makes sense. You typically oversize the VFD by 50-100%. So a 2 HP 3 phase motor would require a VFD rated for 3-5 HP with the associated single phase line side to power it. The VFD would typically be installed in an enclosure that ensures proper dust and cooling for it to run reliably. Generally speaking, if you don't have 3 phase power, you buy single phase tools where you can, change larger motors out, and adapt where you can. For example, you would not really want to go through the trouble of running a 5-10 HP 3 phase motor off a converter.

 

[philshevlin]

Thanks!. For example, I saw a 3 phase 3hp ironworker for sale.

Could I just swap the motor out, rather than go 3 phase? Or is a VFD my best option?

 

[md21722]

Others may chime in. But here's the thing. VFD's are used all the time in industry where 3 phase is the line in and line out. They use the VFD's to vary the frequency (speed). At home use, its typically used to run 3 phase equipment as is, particularly where swapping the motor is an issue, or the need for the frequency (speed) adjustment is helpful. A 3 HP 3 phase would require a 5 HP VFD (#10 30A circuit) and cost some money so if its an on/off machine for you and you can get a 3 HP single motor cheap, go for the 3 HP motor...

 

[CGT80]

A VFD will start at 120-150 bucks and I think mine was 1 or 1.5hp for that price and it runs a 1/2 hp baldor 3 phase grinder. I couldn't change the motor and the grinder was free and worth 400-700 bucks new, so it was a good fit. A VFD can also control the direction and speed of a 3 phase motor, so I can drop the speed below the 3000 rpm on the name plate of the grinder. IIRC, you get almost full power output from a vfd, but I don't know if that still applies when you reduce the speed (an idea for a mill or lathe).

Since I don't know how an ironworker works, I don't know if variable speed will be useful. When guys get 3ph air compressors that are 2 or 3 hp and up, they usually just buy a new motor. My brother changed out the 3 phase motor on our mill for a single phase motor that had a tad more hp, but now I wish we had used a vfd (didn't know about them at the time) so that we could set the pulley to a slow medium speed and then adjust on the fly with the vfd.

The easiest way to do 3 phase is to run a dedicated vfd for each machine. You are not supposed to have any kind of power switch on the 3 phase coming out of the vfd. Maybe you could share a vfd between multiple machines, but it would take more research. People do run multiple machines from a rotary 3 phase converter (an extra 3phase motor spins with no load to make the 3rd leg) and there is info on this forum on that.

 

[Norcal]

Thanks!. For example, I saw a 3 phase 3hp ironworker for sale.

Could I just swap the motor out, rather than go 3 phase? Or is a VFD my best option?

Too many variables to say, if a machine uses a proprietary motor your screwed, or if it has a motor that is not available in a particular frame size in single phase, to name a couple, plus when changing a motor the 3 phase controls probably won't be suitable for single phase, it needs to be evaluated on a case by case basis.

 

[larry_g]

Do not discount a rotary phase converter, RPC, as a way to power your equipment. I have a single RPC that feeds my shop area and 5 different machines off of it for better than 10 years with no problems. Phase Perfect is another option. VFD's are the popular devise for a single motored machine but if the machine has more than one motor or complex controls then it is not the best solution to your problem.

Look at the practical machinest site as they have a whole subforum to discuss these issues
practical machinest


Be fore warned that if you join the PM site it is for professionals and they do not tolerate newb questions well, and even delete threads for a bad title so be careful and consider it a source of information to study.
lg
no neat sig line

 

[A_Pmech]

As a rule, single phase capable VFD's don'the require de-rating. Only VFDs designed for three phase only input require de-rating as the rectifier section is not designed for the additional current a single-phase input would place on it. In any case, the manufacturer's literature will provide sizing assistance.

A 10HP rotary phase converter will power most home shops quite nicely and they will run on a 100A service with no issues. Mine starts and runs my 10HP lathe at essentially full power.

There is no logical reason to avoid three phase equipment if it is something you need or want.

If you will be running your wiring on the surface in conduit, there is really nothing to prepare for. A luxury might be to make a small doghouse outside for a rotary converter so you don'the have to listen to it humm.

 

[philshevlin]

Awesome forum! You guys answered all my questions and even a few I didn't know I had.

Thanks!

 

[Falcon67]

A_Pmech has it. If you have several 3P machines, a rotary would be cheaper from the start. I just have one 3P mill, so my 2 HP VFD does great going from 240V single to 3P. The trick for a VFD is that is has to control the motor directly. On my mill for example, I ended up just gutting the control box and using the switches for control signals to the VFD. I also have a 2HP single phase lathe. If I convert it later to 3P I would buy a separate VFD for it because the control setup would be different. That's where the rotary starts to shine - you get to the 2-3 or more machine level you'd rather not gut every control box and buy separate controllers. That might also affect resale of the machine when it's time to replace or upgrade.