Best Location for Contactor: Input or Output Side of 2400VA 230V/115V Transformer?

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#1 21681425 31 Dec 2018 19:37

Tom Blough Tom Blough

Anonymous
Post #1
21681425 31 Dec 2018 19:37

I'm doing a CNC conversion of a machine tool and I have a 2400VA 230V/115V stepdown transformer providing power for my servo motors. For my e-stop function to kill power to my servo drives, should I put the contactor on the input side of the transformer, or the output side?

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forums-e-stop.pdf Download (84.99 KB)
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#2 21681426 31 Dec 2018 22:14

Rick Curl Rick Curl

Anonymous

Post #2
21681426 31 Dec 2018 22:14

Hi Tom-The schematic you attached shows it on the input side of the transformer, and I think that's the best place for it. Since the function if the E-stop is to kill power in case of an abnormal condition, it's best to kill power to as much of the machine as possible.-Rick
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#3 21681427 31 Dec 2018 22:21

Tom Blough Tom Blough

Anonymous

Post #3
21681427 31 Dec 2018 22:21

Thanks Rick. That was my thinking as well, however I realized the motion control processor I'm using relies on using the e-stop as a reset for various faults and errors as well. I wasn't sure how repeated cycling of power on the transformer would affect it.
#4 21681428 01 Jan 2019 19:55

Rick Curl Rick Curl

Anonymous

Post #4
21681428 01 Jan 2019 19:55

Frequent cycling won't bother the transformer, but since it's pretty big (2400VA), there will be significant inrush current each time it is energized, so the contactor may wear out prematurely unless you oversize it.
-Rick
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#5 21681429 02 Jan 2019 02:47

Tom Blough Tom Blough

Anonymous

Post #5
21681429 02 Jan 2019 02:47

Should be around 10A steady-state on the input side and I have a 40A contactor. Hope that's enough. Thank you for all your help.
#6 21681430 03 Jan 2019 15:30

Cologne LED Cologne LED

Anonymous

Post #6
21681430 03 Jan 2019 15:30

Electrical relays and contactors use a low level control signal to switch a much higher voltage or current supply using a numer of different contact arrangements.
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#7 21681431 03 Jan 2019 21:39

Max Maxfield Max Maxfield

Anonymous

Post #7
21681431 03 Jan 2019 21:39

Hi Cologne -- other users have tried to tell you that it is totally unfair of you to copy and paste other peoples' content without attribution -- in the case of the comment above, for example, you copied this from this page -- the thing you seem to fail to realize is that the other members of this site aren't fools -- as a result of your actions, the main impression I now have of your Cologne LED company is that you plagiarize other people's work.
You have been called out on this behavior before -- you haven't changed your ways -- I just suspended your account.
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Topic summary

For a CNC machine tool conversion using a 2400VA 230V/115V stepdown transformer powering servo motors, it is recommended to place the e-stop contactor on the input side of the transformer to cut power to the entire machine during an emergency. Although frequent cycling of the transformer is not harmful, the large inrush current at energization can cause premature wear of the contactor unless it is appropriately oversized. A 40A contactor is suggested for an estimated 10A steady-state input current. The e-stop also functions as a reset for the motion control processor, so consideration of the contactor's durability under repeated cycling is important.
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Best Location for Contactor: Input or Output Side of 2400VA 230V/115V Transformer?

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Topic summary