Powering a Slider with a Rotary Phase Converter

Assessing whether a phase converter has the capacity to power a piece of equipment, and avoiding damage to the electronic controls of the machine. March 27, 2012

I am purchasing a 2002 Casolin 10' slider with a 9hp/3 phase main motor and 1hp scoring motor. The saw has digital readout for blade angle as well as the motorized digital rip fence option (in other words, some computer electronics which love to break when it's least convenient). I currently operate a 5hp shaper, jointer and bandsaw on this 10hp rotary phase converter with no issues, and I don't intend to operate any of these at the same time (I'm a one man shop). But this saw is double the power and conventional wisdom seems to be that you need 1.5x the machine hp for your idler hp. An experienced Casolin/Adwood rep has told me not to worry - the worst case scenario with my 10hp phase converter will be a slightly sluggish start, and that I won't do any harm at all to the machine. I'm still a bit nervous. Do you think I should be? I'd like not to spend even more money on a 15 or 20 horse converter since I'm cash challenged after buying the slider itself. Anybody running a similar machine off a nearly equal horsepower idler motor?

I should add that the converter is balanced but is a home brew. It was balanced for some unknown load, and presumably not balanced at all loads and conditions. For this reason I was considering maybe getting just a controller panel from American Rotary, which may do a better job balancing the voltages than my DIY model.

Forum Responses
(Cabinetmaking Forum)
From contributor D:
I just bought a SCM 9hp and put it on my 10hp phase converter. I have had no problems with it. When I first hooked it up the phase converter chattered and the saw started slow, but after switching the wire around, it starts right off. It helps to oversize the wire all the way to the saw.

From contributor K:
I run a 7 1/2 hp Altendorf on an American Rotary 20hp but I got the 20hp before the slider because of a 10hp hauncher spinning 25 blades. I would try it on your 10hp first. The slider has virtually no load on startup (a single blade) compared to a heavy cutter stack or compressor.

From the original questioner:
This is very helpful - thanks. My plan was to run 6/4 SOOW from the panel the 50' to the phase converter, which is just a few feet from the slider, then 10 or 8 from the converter to the machine. I'll have to look at my wire size/ampacity chart to confirm. I believe I should breaker the phase converter at 50 amps for the converter/largest machine combination, which in my shop will be this slider.

The Adwood rep explained to me that the scoring motor and the electronics are essentially single phase, picking up one of the three incoming hot legs. I wonder if I can determine which leg it is that runs the electronics and make sure that's one of the legs from the street and not my generated leg, which may be irregular voltage. I guess I have a 2/3 chance of getting it right if I just leave it to chance. My biggest worry is that voltage anomalies in the generated leg could damage a circuit board.

From contributor B:
American Rotary's support people are probably the most qualified to answer your questions, and will doubtless provide the most economical long-term solution. Great folks.

From contributor M:
I would definitely keep the electronics on shore power. If you cannot ID the utility legs (shore power), it would be worthwhile to get a qualified electrician in to scope it out. The phantom (generated) leg is not stable enough to run any digital control circuits as a rule; a rule that could prove very expensive to break. Not worth the risk with the cost of reward so inexpensive.

From contributor I:
I agree with contributor M. If you are good enough with machine wiring, you should have the 3 phase motors running off the convertor and the controllers/low voltage running off direct 220. I have a 9hp slider and the only time I approach its max amp ratings are when ripping thick lumber. PB and MDF panels do not even slow it down unless the blade is dull.

From the original questioner:
Okay, I agree. I will identify the generated leg and be sure it's powering the main motor only and not powering the electronics or the scoring motor (which are both just single 110v), so I just need one of the two street legs. I think I might take the machine in on Thursday or Friday of this week, so ya'll might hear from me again if there's a new wrinkle.

From contributor E:
If you cannot trace the 2 single phase line supply wires through the phase converter to the machine, you can just check the voltage. The manufactured leg will float high (250-270V) when there is no load applied. Once a load is applied, the voltage will drop, but the initial high voltage is usually enough to either shut the saw down or blow the electronics.

From the original questioner:
If I measure the voltage generated by my converter (with no load) by sticking the pins of my volt meter into the female twist lock plug, I get the following readings measured against ground:
I believe the 242v one is the generated leg.

I've set up the machine and it's ready for power. The two electrical control boxes are rat's nests of wiring. I can identify the 10/4 main power supply coming in, and it disappears behind a metal panel but I think it first goes to the main disconnect switch. Four wires go in and out of this main disconnect switch. From there they go all over, making it difficult to impossible for me to trace them.

So my next thought is to open up the 4-square electrical box on the outside of the chassis, the one where the power cord is wired by the installer, and disconnect the existing 10/4 cable ends. I could then connect only the ground and a single 110v hot to only one of the hot lugs, and plug the other end into a regular 110v outlet. Then turn on the electronics (but not the motor of course) and see if the display lights up. If not, move the hot wire to the next terminal and try again, and a third time if necessary to confirm which terminal is connected to the computer.

Does this seem like a good and safe way to proceed?