Posted by Sherman in Idaho [72.47.153.28] on Thursday, May 15, 2014 at 17:19:50 :
In Reply to: Re: 3 phase not a big deal anymore posted by Kaegi [98.247.164.246] on Thursday, May 15, 2014 at 15:57:11 :
I usually use Automation Direct or FactoryMation. The latter is usually a bit cheaper, but has less selection. Automation Direct has free 2-day shipping on larger orders. A half-horse VFD will run you around $130. Maybe not worth it for a simple on/off motor but if you have any desire to control the speed or have a "soft start" feature, or control it with low-voltage pushbuttons located some distance away, even a cheap VFD gives you all that and more. They also incorporate good over-current and under-voltage protection, which can save your motor if something gets bound up or the line voltage droops.
On machine tools, a VFD sure beats all the pulleys and gears they used to use. The only catch is that a VFD is a "constant torque" device, which means that when you slow a motor down, you get proportionally less horsepower out of it. This is fine for pumps and blowers, since the load drops with speed even faster. On machine tools it's usually okay unless you're really pushing for maximum cutting power at slow speeds.