VFD for 3 machines?
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  1. #1
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    Default VFD for 3 machines?

    Am moving into a new shop, currently running a 13 x 40 lathe, manual mill, and 6 x 18 surface grinder, on a rotary phase converter. Am completely new to VFD's, can I run multiple machines, one at a time, on a single VFD?

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    So long as the individual motors meet the requirements of the VFD, I don't see any reason why not. You would have to have a means of disconnecting the non-used motors like a 3 position 3 phase switch. You will have to shut the VFD down each time you want to change motors.

    Tom

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    VFDs for the most part are direct connects from the VFD output to the motor, the VFD motor tuning and parameters are specific to each motor. The controls for the VFD are via low voltage inputs and you cannot use the current switch gear/contactors on the current machines. So the short answer would be that I would not recommend it. You do not just connect each machines power cord to the VFD and have it work as you would with an RPC. Not saying it can't be done, but it is better to install a VFD for each machine if you want to go that route. Also the VFD control system to properly operate each machine would be different. If all the motors were the same and all the machines operated the same then that is a different situation.

    If you want to spend a lot of money on a fixed frequency VFD then you can look at Phase Perfect units, but I would opt. for an RPC based on cost and simplicity when dealing with multiple 3 phase machines.

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    Some of the high-end VFDs on the market have the ability to store 2 sets of motor parameters, I don’t know of any that could store 3. The alternative would be to set up a VFD in simple V/Hz control and give up the better performance you get with vector control, then get 3 sets of overload relays on the output of the VFD, one for each motor, all tied back to the VFD control system and the selection system that you use to choose each motor and isolate the others from the VFD.

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    I just get 3 vfd's from Automationdirect and be done with it. Don't try to use 1 for 3 different motors, a few of the parameters are motor specific

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    Or, if you don't want any headaches with rewiring your machinery, just use an RPC.

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    Hello !

    VFD-motor connection should be minimal length.
    Also, disconnection motor-VFD connection when running can mess up VFD
    And as before said, motor and VFD should be tuned accordingly.

    Nowadays, VFD-s are so cheap that the extra switchgear and wiring could cost more than 3 VFD-s


    Also, if you use vector-control VFD, you could probably have some vibration issues during machining (feedback instability). So, if possible, use simple voltage / frequency control. This has helped me in some cases (especially when there are mechanical flywheels like in press brakes).

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    Thank You. Currently run a RPC, it gets so hot you can't touch it, my lathe 7 1/2 HP 13 X 40, has a "lull?" when starting. Is there a fix for this?

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    Quote Originally Posted by Jraef View Post
    Some of the high-end VFDs on the market have the ability to store 2 sets of motor parameters, I don’t know of any that could store 3. The alternative would be to set up a VFD in simple V/Hz control and give up the better performance you get with vector control, then get 3 sets of overload relays on the output of the VFD, one for each motor, all tied back to the VFD control system and the selection system that you use to choose each motor and isolate the others from the VFD.
    Ok a real dumb question here to the guy that knows.
    Start with a 3 phase machine with a control transformer, a hyd 3 phase pump and a 3 phase spindle.
    If you give up vector control and set for simple can you run such off of a VFD?
    Assume sometimes the spindle on and other times off so pulling it in and out of the VFD feed.
    Can this be made to work as hack if you get inventive with settings?
    Bob

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    Quote Originally Posted by wyelk View Post
    Thank You. Currently run a RPC, it gets so hot you can't touch it, my lathe 7 1/2 HP 13 X 40, has a "lull?" when starting. Is there a fix for this?
    an appropriately sized RPC. They would recommend you get at least double your highest HP motor, so 15HP for you assuming your lathe has the most ponies.

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    Thank You, looking now


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