# Vfds For 2 Motor Machines



## HMF (Oct 15, 2016)

Say you have a milling machine with two motors, a 1 hp 3 phase spindle motor and a separate 1/4 hp table feed motor. You want both converted to 1 phase 220 to use house current. You also want the feed table motor to automatically run only when the spindle is running. 

How have you set this up? (Schematics and photos would be great).


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## JimDawson (Oct 15, 2016)

The easy way is to use separate VFDs to run the motors.  In those sizes VFDs are cheap.

Question on running the feed motor:  Do you want the feed motor to always run when the spindle is running or only allow the feed motor to run when the spindle is running?

Most VFDs have a programmable relay that could be used to interlock the feed motor.  In general, it make more sense to have the feed motor completely separate from spindle motor so you can operate the feed for setup purposes without the spindle running.


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## Eddyde (Oct 15, 2016)

I agree with Jim, 2 VFDs is the way to go. VFDs are designed to run only 1 motor at a time and no controls (switches, etc.) can be wired between the VFD and the motor. Heres a picture of my mill set up with 2 VFDs, one for the spindle, one for the motor that raises and lower the head.


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## mksj (Oct 15, 2016)

As Jim and Eddy outlined, separate VFDs is the easiest and can be put in a single enclosure.  I had a BF30 that had a BLDC drive, I initially added a Z drive with a VFD and then a X axis VFD drive, otherwise I would have put both VFDs in the same enclosure.  Z axis uses a spring return toggle. X axis uses a spring return joystick and two separate high speed momentary buttons, using Bodine gear motor AC drives. All had limit switches. One note on the X axis drive, I originally used a KB VFD drive, inexpensive but did not have sufficient braking capacity.  I subsequently installed a WJ200 which was slightly more expensive, but stopped very quickly. It is possible to use relays either in the VFD or separate to interlock controls. The WJ200 has sufficient power on the 24VDC input supply that you could use two diodes to drive a separate relay that would only turn on when the inputs are on. You need diodes to prevent a back feed from one input to another. This is handy for a coolant circuit to turn on only when the spindle is running.


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## chips&more (Oct 15, 2016)

Are you sure the table feed motor is 3 phase?


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## HMF (Oct 15, 2016)

The feed motor is also 3 phase but only 1/4 hp.

This is to get my van norman #12 going.


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## fixit (Oct 15, 2016)

Where I worked in my other life before retirement we had machines with 6 motors running various part of the total machine. ONE inverter operated ALL motors each motor could be stopped or started as needed with no effect on the inverter. The inverter maintained the speed of all the drives so the process could be ramped up or down as needed. I see no reason why he could not start & stop the 1/4 hp motor as needed using one inverter. Just run the power through a relay & protect it with fuses in all 3 legs. We did this with 3, 5, 7.5 hp motors total of 6 motors from one inverter. Oversize the inverter say 5 hp, set FLA at max, control each motor with a relay & protect each motor with OL's &/or fuses sized for the motor. Truth is you could then operate each motor independent of the other as long as they both ran the same speed. I know it works I worked on them we had 10 machines set up that way.

fixit


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## mksj (Oct 15, 2016)

The use of a single VFD for multiple motors is doable, and works ok when all the motors are running the same speed, but it depends on the VFD settings. Sensorless vector will not work with multiple motors, so you need to use V/Hz fixed setting, and you loose some of the benefits running in the sensorless vector mode. You loose the motor protection properties if you set the VFD for the maximum current/Hp of a number of motors. My recollection on some of these setup was the individual motors need fusing in accordance with their ratings "Each motor connected to the VFD must have its own short circuit and overload protection".  When using the  VFD for an axis feed, the speed is almost always independent of the spindle speed. I think an extra $100-150 for an axis VFD is more practical, then buying a larger VFD to run everything.

http://www.automation.com/library/a...ives-control/vfds-can-control-multiple-motors


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## Keith Foor (Oct 16, 2016)

Well here is another thought.  Do you have or expect to have more than one machine that will have multiple 3 phase motors?  If you are figuring that you will, and will also need 3 phase for welders and other gear you may consider building a RPC that is sized for the accessory motors and a welder and then run your spindle motors with a VFD and run the accessory motors from a RPC.  RPC's are easy to build if you are handy enough to connect a VFD to a machine you can build one.   Running coolant pumps from a VFD is sort of a waste because they need to run full speed for correct flow.  If you are running them on the VFD that is your spindle unit, and you slow the spindle, the pump decreases or stops flowing all together.  

Just a thought.


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