Saturday, January 30, 2010

Phases. Converted.

When I bought my milling machine a couple years ago I was suddenly faced with the challenge of how to create three phase power. I ended up buying a 3hp VFD (Variable Frequency Drive) and hard-wiring it directly to my mill, which worked ok. For some reason, even though the mill was 2hp and the VFD 3hp, the VFD would trip when I started the motor. I had to turn the speed control right down, turn on the motor, and once it was running I could ramp it up to full speed. Other than that minor inconvenience, it was fine. When I bought my D&W bandsaw I took the VFD off the mill and tried to use it, with marginal success. My bandsaw has the original cast iron motor, refurbished, and I've read from several sources that old electric motors don't like the power created by a VFD, and may actually burn out prematurely as a result. Obviously I didn't want that.

Last summer I found an ebay store that sold phase converters either as a complete package or as a kit. I decided to buy a kit and assemble it myself. Essentially a kit contains all the parts necessary to assemble a static phase converter. All you need is a box to assemble it in. The other option is to build a rotary converter, but you need to find a 3 phase motor to use as a slave. Having heard all sorts of bad things about static converters, I opted to try and find a used motor and build a rotary converter. Unfortunately my search for a cheap, or preferably free, motor had been fruitless for months until finally I found a motor from an unlikely source. I had been calling around to scrap yards and surplus dealers to no avail, and then one day last week I decided to call an electrical contractor in town to see if he knew where I might find a cheap used motor. Dart Electric is the company that wired my house, and I learned very quickly that they are meticulous when it comes to billing. Every inch of wire in my house, every marrette and screw was charged back to me at full retail prices. Apprentices were billed out at full journeyman rates, and even when they came back to fix their own screwup they tried to bill me their hours.

Anyhow, I called and chatted with them for a couple minutes and was told to stop by and take a look through their storage sheds. A quick search turned up a 10hp, 3ph motor in what appeared to be good condition. 'It's yours, you're doing me a favor by getting rid of it' I was told. Woohoo!

When I picked the motor up I made a quick stop at the shop where I used to work to chop off the shaft. I didn't want to run the risk of something getting wound up in it, and cutting it off was easier than making a guard.

Looks complicated, but it's pretty simple. The silver capacitors are run caps, and the black capacitors are start caps. The two things in the top are contacts, to switch from start to run caps as needed. Unfortunately the diagram I got with the kit was horrible, but the seller was quick (almost instant in fact) to answer my numerous questions throughout the process.

This is my fancy Sawstop test bench. I was a bit sheepish the first time I fired it up, there's alot of capacitors in that box. I once saw a demonstration of the stored electrical potential in the tiny little capacitors from a disposable camera flash. It was nuts, it melted a screwdriver!

All done, it took about 6 hours total. Initially I thought that I would install the converter near the main panel and run a plug in somewhere near the bandsaw, but I decided it would be better to keep it close so I can turn it on and off as needed. My bandsaw is the only machine that needs 3 phase right now so I hardwired it directly to the converter. I've already noticed how much quieter the D&W runs off the converter compared to the VFD, and I'm happy to see that I can run the converter, bandsaw, and jointer all at once without tripping a breaker.

I'm one step closer to running out of excuses for my lack of woodworking productivity!


jbreau said...

good score, but i guess you probably feel like you bought it from the surplus charges from wiring your house...
electricity is an odd thing.

Cody said...

Electricity hey? Crazy shit. Did you know there's 2 phase power? I just learned that, I guess it's not used much anymore though. I wish everything was three phase. The motors run smoother and they're much smaller. This 10hp weighs about 50lbs, a single phase 10hp would be at least double that. In europe every house is wired with single and 3 phase, and they use 3 phase for the washer, dryer, and stove. Around here 3 phase is called 'Ag Power' and it costs about $5000 to get it run to your property if you don't have it. Makes the $100 I spent on the converter seem miniscule!