3 phase speed control

Mfgr and model number of the VFD?

Bill

tchurchwell wrote:

start over with your questions

1. what do you want to do with the grinder?
2. what do you mean the cheap potentiomenter - do you mean that there is a problem with a vairable resistor, or do you mean something else?

1. the only practical way I know to vary the speed of a 3 phase motor is to change the input frequency. that is what a VFD does.

Sorry I wasn't clearer. The VFD for the grinder is a PWE-05K by Hitachi which converts 230VAC

1-Phase to 230 VAC 3-Phase with variable frequency output from 1-50Hz. Speed can be controlled either by a potentiometer or dip switches. The VFD came with a free "potentiometer" which doesn't work very well--the grinder never gets up to useful speed--but I don't really need to vary the speed of the grinder. The grinder is a 1942 Hammond Combination Chip Breaker and Cup Wheel Grinder with a 1/2 HP 3-phase motor which works fine with the VFD. I would like to upgrade my lathe motor and am considering a 3-phase 3/4-1 HP motor. Most of the cheaper VFDs are static which partially defeats the purpose of the increased HP motor. Since a rotary converter uses a slave 3-phase motor, my questions are:

1. Is there any reason I can't take a power feed off the grinder motor for the 3-phase lathe motor, and, if not,
2. What c> start over with your questions

I have a Hitachi VFD (sorry, forget the model number) with external speed control using a pot. The way mine is configured is the pot controls 0-100% of the programmed speed range. The speed range (in Hz) is programmed in the controller itself. So, if the max frequency 60Hz, then the pot controls up to the nameplate rpm of the motor. If the max frequency is, say, 120 Hz, then the pot controls up to double the nameplate rpm of the motor.

If you gang the 1/2Hp motor with a 1Hp will be increasing the amperage draw approximately 3x through the VFD (actually, a little less, but lets keep it as a safety factor). Instead, why not just move the grinder's VFD to control only the lathe? That is, as long as your lathe motor doesn't draw more amperage than the VFD can handle.

My Hitachi is programmable for fwd/rev and is controlled using an external double-throw switch.

Most vfds support a number of different options as to controls -- a pot for speed, a number of different switch configurations for start/stop/direction. A good, serviceable pot, btw, will cost you a couple of bucks at Radio Shack. The box to put it in and a nice nob will cost you more than the pot. See if your vfd supports '3 wire control'

-- the best to use for start/stop if supported.

Also, the vfd parameters control the min and max rpm, how much power will be imparted to the motor, etc.

Further -- there are 3 phase motors and 3 phase motors which are rated to be run from VFDs. Low speed running causes the motor to heat up and the vfd rated motors have high temperature windings and better cooling systems.

"Ganging" two motors on the vfd will cause more problems than just too much current draw. Most vfds read the back emf from the motor and two motors will confuse the little computer driving things. Also, it is likely that your grinder doesn't get to a reasonable rpm because the parameters in the VFD are set up incorrectly.

This is not as easy as falling off a log. What you really need to do is read and understand the manual for the vfd you have -- they are all different. You will also probably need to enlist the help of somebody who understands the ins and outs of vfds. You can trade them something within your area of expertise.

Bill

Dan Boll>> The VFD for the grinder is a PWE-05K by Hitachi which converts 230VAC

I can't find a manual for that drive on-line or I might be able to help. Sorry,

Bill

tchurchwell wrote:

go to my web site,

click on vacuum pumps - one of the first few pumps I offer there has a link to an article on how to make a static converter - all you need is a capacitor and a relay. Read the article. Make one for your grinder. Take the Hitachi unit and use it on the lathe. The problem is almost guaranteed to be the way the unit is programmed, not the pot - read the manual, or photocopy it and send it to Bill R or to me, or to someone else familar with the technology.

by the way, I may have a spare VFD that would drive your grinder if you really want to use such technology - you can contact me off the list through my web site if you want to pursue that, but you don't need to - I run my mill on a static converter with a single capacitor and a single relay - works fine, and that mill has a 6 hp and a 2 hp motor on it - don't see why a similar simple static converter won't work for your grinder. I use VFDs on my lathes where I want to vary the speed directly.

Thanks again to all for your help. I must confess that I copped out. I found a reasonably priced DC motor and controller on eBay. So for slightly more dollars and a lot less time spent mastering electornics, I can spend my time learning to turn. (And not screw up my grinder which works fine). Thanks