Help Wiring Three-Phase at Home

Hey all,

So I'm in the market for a mill, most likely I'll end up purchasing a BP (Yes, Yes, groan all ye' want) since its within my price range, parts are easy to come by, and there is a ton of info on the web about them. So now for my dilemma. I live in the Chicago-land area, and we have the standard US power grid, 120+, 120-, and Ground. So Now for my question.

Im looking into getting a three-phase mill, and lathe in the near future. These rickety old benchtop ones are a pain. (Nothing like seeing the table shake as you do any sort of cutting xD)

So I'm a tad confused as to how I should go about wiring this stuff up. I'm failry good at circuitry and logic circuits, but AC is a bit of a different demon. So if Im running a 3 phase motor I know I will need to make/buy a rotary phase converter. Now, 3 phase power has 4 wires, 3 hot and a neutral? So If I am wiring up a rotary converter, would I connect my arbitrarily + wire to a motor terminal, and the - to the neutral pole? Will I have to make the neutral terminal on my machine the -120v? I'm a tad bit confused :P I just wish I had my physics book handy...

We have a devoted forum section with massive amounts of information.

Forget neutral for the time being. A three phase machine that runs on 240 wants three hot legs, period.

They are often grounded (earthed?), but that has absolutely nothing to do with making the motor run.

johnoder said:

We have a devoted forum section with massive amounts of information.

Forget neutral for the time being. A three phase machine that runs on 240 wants three hot legs, period.

They are often grounded (earthed?), but that has absolutely nothing to do with making the motor run.

Click to expand...

That makes sense. I've seen alot of info about 4 and 3 wire wiring for motors. Could you point me in the direction of this El Dorado of 3 phase?

Much thanks

-Tom

There has also been some good discussion in the Bridgeport and Hardinge forum. I posted this a while ago, and it is pertinent here as well:

http://www.practicalmachinist.com/v...ls-lathes/best-bridgports-230260/#post1626691

Dennis

Trofenstein,

Yo may be jumping to a conclusion here when you say you will need a rotary phase converter (RPC). This may end up being so, but do not reject out of hand other options, which may prove to be not only more satisfying but maybe easier to implement.

If your Bridgeport has only one three phase motor (no three phase feed motors or coolant pumps, etc) and you do not envision running other three phase motors in your shop, I suggest you consider a VFD, which gives you many more features than an RPC at what will likely be a comparable price (unless you plan to make your own RPC). Programmable starting speed ramp, variable speed and built-in motor protection are but a few of the advantages. The only disadvantage I can think of is that you will probably not be able to achieve the instant reversing you need for things like tapping, and if you don't need that feature, you're home free.

Where the RPC really shines is a shop with several three phase machines, where the price of a VFD for each machine becomes an issue, and for machines with multiple motors, as alluded to above. But even in these situations, the VFD's advantages can be so compelling that you will find a mix of power methodologies in the same shop.

Steve

on edit, you should have been in Detroit yesterday. I saw a Bridgeport in the craigslist FREE ads - poster said it worked, but needed to go as the building had to be vacated.

Yes, check out the forum section devoted to converters and VFDs. In a nutshell, from standard residential 120/240V "single-phase" supply, you have two main paths, which you should read about: 1.) phase converters, both static and rotary, and 2.) VFD. Fairly easy directions are typically supplied with phase converters or VFDs, although VFDs have a lot more features and capabilities that require more setup and fiddling, I think. I currently use a purchased static converter with a slave motor permanently wired in to make it into a quasi-rotary converter. This works OK, but I have been seriously considering VFD purchase.

If you are just trying to get started you need to look into Static Converters.
I am running two Ironworkers and a Cincy Hydrashift Lathe (1-3hp and 2-5hp) off of one that I built for $45. 5 years ago.
I found the instructions online and there are some in the converter section on this board.