Created Date: February 10,2003

Created by: Lancie1

Dusty,

Yes, you may use 1 Variable Frequency Drive to run two different motors. I did the same thing once, but my motors were both the same size. Because you have a 3 hp and a 1/2 hp, it gets more difficult to set the drive overload parameters. You may need an additional external overload device for each motor, unless you already have existing motor starters for each motor.

But here is what worked for my case. I used a two-contactor motor starter and wired it to the output side of the drive. The starter that I used was called a "Reversing " motor starter (if you are looking it up in a catalog). Just wire it up so each of your motors runs the right direction. Then you can select which one runs by energizing the appropriate coil on the starter. You probaly should wire up an interlock circuit to make it impossible to switch motors while the VFD is enabled. There are some brands of VFDs that can be damaged if disconnected under load. If the situation allows for manual switching, then get a Reversing Drum Switch, such as a Square-D class 2601, type AG2 or BG1. Email me at Lancie1@aol.com if you need further help.

Created Date: February 12,2003

Created by: ericn

I think there's some confusion about the term "motor starter ". I think "contactor " (the "big relay " portion) and "overload relay " (Lancie's "overload device ") might be better terms to use here?

You need some way to select which motor get connected to the drive, and therefore, two contactors will be required. You could use a drum switch, but I think it will be too easy to "forget " to disable the drive before changing motors.

You don't HAVE to, but it's a R-E-A-L-L-Y good idea to place a mechanical interlock between the two contactors (see A-D's BM0H). Also interlock them electrically. There will be lots of smoke if the two contactors happen to close at the same time!... http://forum1.automationdirect.com/board/eek.gif

One problem with running a 1/2HP and 3HP off the same drive will be the lack of overload protection for the 1/2HP motor. If you set the parameters to run the 3HP motor, these will be way too high for the 1/2HP motor. Unless you want to change all the parameters everytime you switch motors, put a correctly sized overload relay on the load side of the 1/2HP's contactor to save the 1/2HP motor from damage (and connect the overload's NC contact in series with the drive enable circuit so it will disable the drive).

You could use a PLC to communicate with the drive and automatically change the parameters, but I don't think this project needs to be that fancy... http://forum1.automationdirect.com/board/smile.gif

Why not just avoid the aggravation and add a GS1-10P5 drive for the 1/2HP motor. You can beat the price! http://forum1.automationdirect.com/board/cool.gif

-Eric