Useful information about home-shop-built and commercial phase converters:

Phase converters and the related wiring can be dangerous if not properly designed and constructed so please be careful and either know what you're doing or find help.

Click here for Bob's Seattle area resources page

Bob's Favorite

The best all-around choice  for a home shop, for machine tools in the 1 hp to 10 hp range, is a self-starting rotary converter that is manually switched on using a "disconnect" or "safety switch", and uses run capacitors to balance the output.

Use the George Carlson design, link below, that uses a potential relay to automatically start the idler motor when the converter is switched on.

The major components are:
- "disconnect" switch to switch the converter on/off
- idler motor, a 3 phase motor similar in size to your largest load
- potential relay from Grainger
- motor-start capacitors for the start circuit
- motor-run capacitors to balance the output
- contactor (high-current relay) to switch the start capacitors
Plus whatever wiring and connectors.

You can buy everything including the motor from Grainger, MSC etc. but it's cheaper to buy used or surplus components. Everything but the potential relay can be found from Surplus Center, link on my FAQ page.

You can wire it into a panel and run 3-phase fixed wiring and receptacles, or you can put it in a box with several receptacles and just plug all your 3-phase machines into the converter.

GWM Corp. background literature

GWM Corp. manufactures a fine line of converters, and as part of their marketing and support they have a comprehensive guide to the sizing and design of converters for each type of load - e.g. machine tools, welders, compressors.

Link to GWM Corp. pages

Read this to understand what kind of converter you need and its required rating.

George Carlson, self-start using potential relay

George Carlson's is my favorite converter how-to page. George's design using the $20 "potential relay" from Grainger is by far the simplest, nicest automatic-start design. The potential relay automatically engages the start capacitors for just as long as they are needed -- no need to hold down a pushbutton for just exactly long enough.

If you're building a 3hp or larger converter, the potential relay contacts alone aren't rated for the required load, so you'll need to use the relay to slave a higher current contactor. Again, George makes this pretty clear.

I don't know where to get potential relays other than Grainger   but they sell only to businesses.   You can try to open an account with them, or find a friend who qualifies and can order.

Link to George Carlson's converter pages

Jim Hanrahan's converter article

Jim's is the other how-to article at least that I'm aware of. Jim's article provides more theoretical information. His self-start design uses a two-pole pushbutton to start the idler by engaging the start circuit for exactly as long as you hold down the button. This is fine if it's your shop, but is not as safe as the potential relay self-start because someone unfamiliar with its operation may release the button before the idler can stay spinning, and burn up the idler if it isn't properly overload-protected.

Link to Jim Hanrahan's pages