View Full Version : Phase Converters
09-18-2001, 12:16 AM
If anybody has experience running 3 phase machines on phase converters, I would like to hear all about it.
If there is already a thread with this topic, then just direct me to it.
09-18-2001, 05:46 AM
They work, I run a homegrown unit myself at home, someday I'll get the 3ph in from power company. But then they will want to charge me commercial rate, so I am running converter.
One has a power droppage with a converter, not bad but it is there. I have had little problem, my Vert mill grunts when going for-rev.
The latest greatest is a VFD unit, they offer full torque and the frequency is variable and thus the rpm. And they are getting cheap.
Hate to pull anyone away from this board but there is a section on this at www.practicalmachinist.com (http://www.practicalmachinist.com) it is also a continual discussion over at the www.chaski (http://www.chaski) board.
Scroll down on this board and look, you might use the search button.
I think the best way to do it with with a VFD (variable-frequency drive). They take in 230V single-phase and put out an excellent approximation of 230V 3-phase, with variable frequency so you get speed control in the bargain. As Halfnut says, they are getting cheap, if you buy on the surplus market. See, for instance, http://www.dealerselectric.com/ (click on "inverter drives") or http://www.vfds.com
(Usual disclaimers.) There are other web sites offering surplus drives as well, and I've seen an ad for them in Home Shop Machinist.
I've got one on my milling machine, and it's great.
I used to have a "static phase converter," which is just a capacitor and relay to give an initial phase shift to get the motor spinning, at which point the motor runs on single-phase. It worked, sorta, but the motor never seemed all that happy and I could easily stall it when drilling 1/2" holes. With the VFD, I've got torque galore and easy speed control.
09-19-2001, 01:54 AM
I agree with the VFD. The best ones have IGFET drivers and can handle a full power reverse. Special 3ph VSD motors are available to take full advantage of the VFD to get real gut wrenching torque at minimum rpms.
If you go with a 3 phase converter the rotary type is the best for shop use. You will want to get a HP rating higher than your shops needs to ensure smooth operation.
The only static converters I have had experience with is big 100HP unts for pumpjack operations where 3phase cannot be brought in. When you don't have any choice - they sort of work.
09-19-2001, 07:29 PM
I run a static phase converter in my shop, the advantage it does have is that it is relatively cheap compared to a rotary model converter, VFD, or bringing in real 3phase. There are some additional limitations that you have to live with a static converter. They are sized to the horsepower of the motors that you are using. In my case, to be able to run my SB Lathe (5 hp) and also the power feed to my mill (1HP) I had to get a unit rated at 5-7HP. To run the mill I start the lathe first and then the mill/power feed. This is a pain but I can live with it in a hobby shop. One advantage to this is that the motor in the lathe acts as what the manufacturer calls an “electric flywheel” to help smooth the power output. The other major disadvantage is that you lose a certain amount of horsepower with this setup. The best advice is to look very carefully at the manufacturer’s product information before you buy.
09-20-2001, 05:43 AM
The reason that I have been using a homemade rotary converter is very simple. I was thinking about what I had directly invested in mine.
3 phase motor for idler, came off wash bay pump at work, had a broken off shaft, was free with a scrap pass.
Washing machine motor, who knows, probably followed me home from an auction, people also give me good junk. That happens when you share your scroungings, they multiply.
A couple of pulleys, same type of source as wm motor, one had a little chunk out of rim.
A used belt, I think it used to be on my pickup.
Wire nuts, bought a whole bag at Johnsons auction for a dollar or 2, maybe it was 2 bags, anyway I got a bunch of them.
The base is a piece of channel iron left over from making my trailer.
Only real direct cost was the welding rod I stuck the steel pulley to the broken shaft with, runs pretty close. I also stuck down the two motors with the welding rod. Bad I know, I have a couple of hand grinders that do a good job of unwelding.
Total direct cost less than a buck, been using it for 5 years. Have it in another room now, it is even quiet that way.
I do have great hopes with another 3ph motor I have scrounged, cost me 20 bucks, exensive I know, is a 15hp, am thinking about building a hybrid setup, the smaller motor for light loads but have the bigger one for bigger ones. I have 3 DC welders sitting in shop and all are 3ph. I think this 15hp will turn my Lincoln SA Jr 175. WWHHHHHHHRRRRRRR.