What Type Of Switch?

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Plas62

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I am looking at using 1 VFD (KBAC 27D) to control three separate motor setups on grinders. none of the grinders would be used at the same time.

Two of the grinders would have 3ph, 230/460 vac,1.5hp motors with FLA of 4.8 amps.

One of the grinders would have two 3ph, 230/460 vac,3/4 hp motors with FLA of 2.8 amps each, 5.6 amps total.

What type of switch would I need for this application?

Jim
 
This is a very unorthodox setup. To have 1 drive operate multiple motors, they are typically all the same HP. Using a drive loaded with parameters for one motor will not be setup correctly for a smaller (or larger) sized motor. You will end up with a motor that is inadequately protected. Aside from that, at the very least, you will need interlocked contactors on the load side of the drive. The start / stop circuit should engage the appropriate contactor before the drive is started and disengage the contactor after the drive has stopped. Drives are incredibly capable. They will have a problem with the sudden addition of motor load after starting. Likewise, they have a huge problem with a motor suddenly disconnected.


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mzayd3 said:
This is a very unorthodox setup.
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I agree. If you insist on doing this I suggest that you put cords and plugs on the machines and put the VFD in a box with a receptacle. You will need to reconfigure the VFD each time you change machines. Put a disconnect ahead of the VFD and never plug or unplug a machine with that disconnect closed. The alternative would be to spend more on contactors, relays, switches, and enclosures than the price of two more VFDs.

Unless, that is, you already have the contactors. Did these machines come with controllers?
 
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As @mzayrd3 said it is a rather unorthodox setup. But I would use twist lock plugs, male on the grinders, female coming out of the VFD. That way, no switches are needed between the VFD and the grinders and you can only plug one in at a time. Turn on the grinders with the VFD. Set the VFD for the highest motor load (5.6 amps). You will not have proper overload protection, but it will work. This would not be my first choice of setups.
 
Plas62 said:
I am looking at using 1 VFD (KBAC 27D) to control three separate motor setups on grinders. none of the grinders would be used at the same time.

Two of the grinders would have 3ph, 230/460 vac,1.5hp motors with FLA of 4.8 amps.

One of the grinders would have two 3ph, 230/460 vac,3/4 hp motors with FLA of 2.8 amps each, 5.6 amps total.

What type of switch would I need for this application?

Jim
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I would lean towards a RPG and not a vfd . They are very forgiving & not sensitive to open circuit conditions. You could interconnect each machine with it's own power contactor. A rotary selector switch would give power isolation between machines to select the contactor coils.
 
uncle harry said:
A rotary selector switch would give power isolation between machines to select the contactor coils.
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No need. You can just treat the rotary converter as a source of three-phase and hook up the machines as you would if you had three-phase service.
 
Plas62 said:
I am looking at using 1 VFD (KBAC 27D) to control three separate motor setups on grinders. none of the grinders would be used at the same time.

Two of the grinders would have 3ph, 230/460 vac,1.5hp motors with FLA of 4.8 amps.

One of the grinders would have two 3ph, 230/460 vac,3/4 hp motors with FLA of 2.8 amps each, 5.6 amps total.

What type of switch would I need for this application?

Jim
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That VFD uses sensorless flux vector control. It is a very nice one but is likely to be unhappy driving two motors at once.
 
By the time you install the necessary switches and wiring you could pay for a rotary phase converter and go that route. No switches needed other than the standard switches already on the machine. Granted, it would not give you variable speed, but I don't think you will need variable speed for grinders anyway.
 
John Hasler said:
No need. You can just treat the rotary converter as a source of three-phase and hook up the machines as you would if you had three-phase service.
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Agreed. My only concern would be the temptation of starting more than 1 machine at a time. This way the RPG need only be large enough for 1 2/2 the HP of the biggest load.
 
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