VFD, phase converters????my brain hurts..

[Gary Conklin]

Ok, I know there are some electric guys out there that can help me out with this one. I am looking into some lathe stuff and can't seem to wrap my head around something.

I think I have the first part: If I get a 3 phase 3hp motor, I will need to get a rotary phase converter, and run a 220 line, right?

Now here is the part I stuck on: I was looking at some VFD's and they also appear to be phase converters, and are also used to control the speed of the motor???

In the end I would like to be able to set up an AC electric motor, have enough HP & torque to turn large items, but also be able to turn from 0-1500 Rpm.

Man I barely do the woodworking thin well, this electricty thing is making my brain hurt.

[Scott Conners]

Gary, you have it pretty much straight. Most on here would suggest the VFD route, as it provides variable electronic speed control. http://www.surpluscenter.com/ is a popular source for motors and VFDs, the Teco VFDs seem to be very popular. I'm pretty sure that 3hp is big enough that it would require a 220V 1phase circuit to run it, I've only seen up to 1.5hp on a 110V inverter.

[Dennis Ford]

You are correct in that a VFD can be a phase converter (if you get one that accepts single phase input). It sounds like a VFD is where you are headed.

0 - 1500 rpm with good torque is a tough spec to meet unless you also have some mechanical speed changes (usually done via belt/pulley changes). I am not saying it can't be done but it would be easier & less expensive if you can live with ranges like 50 - 800 rpm and 100 - 1600 rpm. I just made those numbers up, your actual numbers would depend on several variables. By moving a belt in the example above, you would double the torque at the spindle using the low range.

[Jeff Nicol]

Gary, A rotary phase converter is another motor that starts the 3ph motor spinning with 1ph voltage. When the 3ph motor gets spinning it will create or generate the third leg of the power needed to run the big motor. The main difference is that a large rotary converter can run more than one 3ph motor if it is rated high enough to handle the HP of the motors being used. They would be good for a shop that does not have 3ph power available and all the machines were rated for 3ph power input. With a VFD you control each motor individually and have a better control of the varible speed. You may lose some of the total power rating on the the motor with a VFD but not much. There are also static phase converters available but they usually run the motor at about 60% of the rated HP. That is what I know, and they all work, pros and cons to all and the wieght of a rotary conveter is a big one plus cost! VFD'S work so well if you need variable speed. The others can be variable speed but most of the time the machine will have it already built in by either gears or varible pulley/belt systems as the converter itself is not varied. There is tons of info out there on the subject and this is a brief look at it.

Hope it helps,

Jeff

[Rich Souchek]

Gary,
It hurt my brain also when going thru some of the same questions...
Turns out, the VFD will convert a 220 volt single phase power input into a 3 phase output.
One of the keys items in the cost is the motor horsepower. A VFD for 2 hp and under is relatively cheap, but the cost steps up for more than 2 hp.
My suggestion, and what I did, was to call one of the big VFD companies and ask their sales/technical help people some question. I went with Automation Direct, and they are showing a model GS2-23P0 for about $300 for 3 hp, 220 volt single phase in.
I got their simpler version for 2 hp about 2 years ago and am real happy with it.
Hope this helps.
Rich S.

[Dave Schell]

Gary, I did a lot of research on VFDs when I built my barebones Vicmarc and settled for the Hitachi x200 for one reason: the user manual. I knew I was going to be flying solo in configuring the paramters and wiring it and a remote control, and the Hitachi models have the easiest to understand documentation out there.

Here is the 3HP model I bought for $255: http://www.driveswarehouse.com/Drive...54d29974048f60

[Alex Shanku]

Best VFD's for the price AND warranty are

http://www.factorymation.com/s.nl/sc.2/category.13/.f

TECO FM50 series.


Now, what you want to think about is this: How are you going to switch your machines on and off? If you have your VFD close to your machine, then you can either use the button on the face of the VFD, or you can run some thin gauge wire from the VFD to an existing manual starter/switch on the machine.

You get into problems, like I do, when you try to run numerous machines off of your VFD. This is where having a RPC is advantageous, as you can use your machines starters, both manual and magnetic, as they were intended without further wiring.

Just something to think about.