I am days away from purchasing my first widebelt (bout time!). It is an 18 hp machine. I was thinking of getting a 25 hp rotary phase converter. Will a 20 hp be enough? This is the only 3 phase machine I own. Someday I may have more, but I can not afford to get a ginormous converter. Once I have the correct size, is it easy enough to hook up myself, or should I get an electrician over here? I'm no slouch, but I'm also not a master electrician. I don't want to screw this up.
From contributor G:
I have pretty much the setup you are looking at. 18hp sander, along with a bunch of other 3ph machines. I bought a 30hp rated converter along with the sander. It is a heavy load at startup, so size your system accordingly. It won't cost much more to do it right. As a bonus, you can run the rest of the shop on it as well as you grow. I would have an electrician wire up a sub-panel for the 3ph system. This is a lot of power, so unless you really know what you're doing, leave it to the pros.
On the flip side, our converter pulls 70 amps constant from our single phase service 8 hours a day constant plus various short term spikes during machine startup, but if you're only going to be running the converter during the time you're going to run your sander, oversize the converter.
Be sure you have sufficient ampacity on the converter's input side to allow for starting - I sized the wire run to my shop for the running amperage of the converter, so needed a workaround to get it sufficient starting amperage.
Wiring's not a big deal - I'm no electrical whiz, but comfortable around panel work and the like, and my installation was trouble free. I bought mine through American Rotary, and they were a lot of help with sizing and walking me through the install. Great support, and highly recommended.
The converters are sized based upon maximum load, and if you get a rotary from a well known company, then a 20 hp will start up your sander. I used to have a Butfering 109, and my rotary started it just fine (I used a 15 and a 7.5 hp Kay converter back to back). I switched over to the Phase Perfect after having issues starting my Martin shaper (2 speed motor) and could not get it into the second speed using the rotary converters. The Phase Perfect works great. I now have a Kundig sander with a 25 hp motor and dual belts. I also checked the amount of amps the rotary pulled when idle. It was huge. The Phase Perfect uses 750 watts of power when idle.
Phase converters do not change the Hz. We are on 60 Hz in USA and if you are buying a sander intended for USA 230 V 60Hz you are fine. They are typically the same motor for 50 or 60 Hz, and the motor will spin faster at 60 Hz, but since there are pulleys that are sized, the head speed is the same.
If you do go with a rotary converter, be sure that you use the 2 phases from the utility to run all control circuits. The third phase only goes to motors. When the sander is installed, they should be able to figure this out. With a digital converter you do not have to worry.
By the way, all the phase converter is doing is offsetting one of the phases so it is 120 degrees from the others. A rotary converter works by running a 3-phase motor and using the output of that motor to create the third phase. A standard motor can generate power if an external source is spinning it. A digital converter does not have moving parts; it electronically generates the third phase, and thus is much more power efficient. I found that my machines ran cooler and smoother starts after changing to the Phase Perfect.