Building a phase converter

[Chris Holder]

Hey guys,

For those of you that saw my Dewalt RAS thread, I recently had a very good condition 1959 Dewalt GE radial arm saw follow me home. I bought it at an auction for almost nothing, but it has a 3 phase motor. If not for the cool factor of this tool, I think I might have just resold it, but radial arm saws don't bring much money these days as they seem to be out of favor. So alas, I need a phase converter. This was something I've been thinking about building for a while, but the cost and lack of need (I didn't have any other 3 phase tools at the time) kept me from doing it. Thought I would include you all on the build. Would love to hear any thoughts or ideas. I already decided to go the rotary route (vs. VFD), as the motor is pretty big on the saw and I think I can source parts to build the RPC myself for a reasonably low cost. First up, I need a motor.

[Chris Holder]

This is a FUJI ring compressor. I honestly don't know exactly what it was being used for in it's earlier life, but I found it an another auction for $50. It has a 8-10 HP 3 phase motor on it which should do nicely for my needs.414495

[Chris Holder]

Need to tear off some of the giant amounts of crap and cast iron I won't be using....414500414501

[Chris Holder]

Next a little layout work. I am no electrician, but have a pretty good grasp on what I need in the various circuits. Here is a short video of the layout of the various legs with a start capacitor in place to start that giant motor.414502414502414502 Sorry for the fuzzy photos. I realized I only took a video of this part and had to video capture these.

[Chris Holder]

I'm now working on final layout. I found an old service panel in my stash and sandblasted it so that it will be paint ready. It was in indoor panel, so I will use a piece of 16 gauge for the cover as I don't like the look of the flush mount cover mounted ON the wall. It also wouldn't be deep enough for the starter coil once it is mounted on the din rail if I used the other cover. 414503 The terminal strips are home depot. I will likely bridge each of these in the final assembly (as needed). These represent L1, L2, L3(ghost), and ground. My input wire is #10 MC. I was debating using #8, but I did test everything and max amps at startup were under 25 from the pony motor, and negligible when I turn on the saw.

[Chris Holder]

Most of the parts (with the exception of the wiring, terminal ends, and motor) I picked up off ebay. I won't go into balancing of the voltages as there are plenty of youtube videos on this, but I ended up with all of my capacitors between L1 and L3. If anyone is curious on parts, PM me. These 3 phase motors are so efficient, I will only need a 20 AMP breaker for the saw itself. 414504414505414506414507

[Chris Holder]

In my original layout, I used a momentary switch to control the start capacitor. I'm working on a way to automate this in my final build, and will post some pics once I work that out. More to come.

[Dan Friedrichs]

Cool! I'm excited to see how this goes! Thanks for writing it up.

[Doug Garson]

You should contact Jack Forsberg I think he is a member here if not he has a Youtube channel and is a member on a Canadian woodworking forum, he is an expert on 3 phase conversions might save you some grief.

[Jerome Stanek]

Until you get all the parts if you wire the motor up and output the third leg you could use a trick that the old carnies used. Wrap a rope around the pulley and pull start the motor to spin the motor up and it will produce the third leg

[Bill Dufour]

That rope start test is probably a good thing to do before you commit to that motor and buy the needed capacitors, make a custom mount etc. There is only so much that a megger can tell you about a motor. A full voltage rotating test may reveal problems that a static test missed. I can tell you I have had to replace several fuses that tested good in my life. Bearing may feel good when spun by hand but start to howl after running a few minutes if the grease is old. Since you bought a used motor the grease is old.
The 40 year old bearing on my lathe motor only howled when the shop got below 50 degrees. The old grease had dried out and got stiff. The cold weather made it stiff enough that it howled until it warmed up by spinning. I could probably have cured it by cleaning and regreasing but new bearings where cheap enough and pulling the motor is a hassle on that machine.
Bill D.

[Chris Holder]

Thanks Bill. I had most of the parts and everything has been tested. Motor is good!

[Chris Holder]

Made a little progress today. In testing, I was using a momentary switch to operate the start capacitor and ultimately the slave motor. In my final build, I wanted a solution to do this automatically. I found a timer relay, which, when paired with a simple relay that can handle the current, should do the trick.414631

[Chris Holder]

I also did some work on the box. I am cheap and did not want to pony up $100+ for a new enclosure, so I am using a box that was once in my grandad's house. It had been around the block and I think most of the knockouts were open, so I am filling in lots of holes. I needed to make a new cover for it, so grabbed some scrap 16 gauge and cut this one out. here it is with the new holes for mounting screws. I also could not find screws with the right thread for the holes, so I retapped for #10 screws, which I already had.414632414633

[Chris Holder]

I think this timer is kind of cool and it would be nice to be able to make my final adjustments to it once the box is closed, so I need to cut a hold in the top. This was a bit tricky with just the angle grinder, but, after a few minutes of laying it out, cutting and filing to final size, we have a good fit.414634 I also pulled wire into my main breaker panel and ran it along the wall. It is about 100 degrees outside right now in North Texas, and even though I have AC in the shop, at the ceiling where I pulled and installed the wire, it was NOT cool. Several hours of pulling and hanging MC and I have the wire to the location for the new box. Hope finalize a few details, paint and get it in this week:)
Will keep you guys posted.

[Rod Sheridan]

Hi Chris, I've used voltage sensing relays to disconnect the start capacitor at 85% of rated line voltage.......Rod.