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Should I apply 3 phase power before drive is awake?

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Hi all. I have a Kinetix 350 and an AB TLY servo motor. I'm using the drive's STO function. AC power is supplied into the drive, passing through an "M1" contactor. It makes sense to m e to keep that contactor open, preventing AC power to the drive, until the drive is fully awake. 

Is that what you guys do? Someone suggested to me in another forum ( http://www.plctalk.net/qanda/showthread.php?t=121021&highlight=drive+awake ) that there is no reason not to supply power to the drive right away because the STO function is inhibiting power to the motor anyway. 

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I would never drop the line power to the drive.  It is never a good idea to duty cycle any drive.  That's why there is the STO functionality is there.

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What is the point of a big "M1" contactor upstream of the drive then? It seems that one wouldn't need it at all. It seems that it would be most efficient to just wire directly from the branch circuit protection to the drive AC input power. 

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Posted (edited)

Yes.  In my opinion the contactor is not needed.

Edited by pcmccartney1

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We installed a Kinetix 6500 drive in a machine. It called for a contactor at the line input that wasn't energized until the drive was awake, kind of like you're talking about. There is a relay output on the drive that we used to control the contactor. Power for the contactor coil is above all safety circuits, so once the drive control stage is awake and turns on the relay output, the contactor pulls in and never drops out until power is dropped to the whole system, which happens very rarely.

This function is described in the user manual for the drive (page 72). It says that control power needs to be applied prior to 3-phase power (among other things).

We haven't used any of the 350s before, but I wouldn't be surprised if they have a similar requirement.

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On the lower kw versions of the drives there is no separate inputs for "Control Voltage", they derive there control power from the incoming power.  For the larger kw, sometimes called the HV models, control voltage (generally 120VAC 1-Phase) allows for the "brains" of the drive to power-up.

Regardless, I've never needed a contactor on the line side of any of the their servo drives or vfds, as long as I've had STOs that I'm in control of.

Just not a fan of duty cycling servo or vfd drives.

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3 minutes ago, pcmccartney1 said:

On the lower kw versions of the drives there is no separate inputs for "Control Voltage", they derive there control power from the incoming power.  For the larger kw, sometimes called the HV models, control voltage (generally 120VAC 1-Phase) allows for the "brains" of the drive to power-up.

Regardless, I've never needed a contactor on the line side of any of the their servo drives or vfds, as long as I've had STOs that I'm in control of.

Just not a fan of duty cycling servo or vfd drives.

I agree 100% about not power cycling drives. I only used this line contactor because the manual said to. It may have been totally fine without it. It only turns off when control power to the drive is dropped, which only happens when power to the whole machine is dropped (or a fuse blows, or similar). It basically just delays the application of 3-phase power to the drive until the control side is up. Once it's on, it stays on. The STO signals handle the safety function.

I went back and forth with AB for a while trying to achieve a safe stop of a newer PowerFlex DC drive without STO. They finally clarified that, since there is no DC bus (and therefore no capacitors or inrush issues) it was fine to power-cycle the 480 as often as needed. It gets control power from a separate source. On that one, we ended up using redundant contactors feeding the 3-phase supply of the drive. That's the only application we've installed recently that power-cycles the mains on a drive.

Kinetix-LineContactor.PNG

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