Contactor Coil Voltage Correction

[YIGO]

I was given a coil that picks at 65% of rated voltage which is 115 V.
If I want to perform calculation on 120 V basis, how would I correct the pick up voltage.
Thanks
Yigo

 

[davidbeach]

Math...

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Compositepro]

This seems like a trick question. The rated voltage has not changed, so the pick-up voltage doesn't change.

 

[waross]

Standard system voltage ratings are multiples of 120 Volts.
Standard motor voltage ratings are multiples of 115 Volts to allow for voltage drop in the conductors.
115 Volt motors are intended to run on 120 Volt systems.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

At any voltage imaginable the relay will pick-up at 65% of 115V.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Or:
65% of 115 = 74.75 Volts pickop.
62.29% of 120 Volts = 74,75 Volts pickup.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr YIGO
The coil picks up at 65% of rated voltage which is 115V. Pick up voltage is 0.65 x 115V = 74.75V. No calculation is needed at 120V. It will pick up at the same voltage at 74.75V ..
You can try it out on a say 200V source through a variac by increasing the voltage slowly and observe the pick up voltage is the same; irrespective of what the final voltage may be.
Caution: 1. test it with the same frequency or dc per the coil label.
2. Stop the test immediately once the coil picks up and reading recorded. Do NOT maintain 200V on a 115V coil.
Che Kuan Yau (Singapore)

 

[YIGO]

I found what I was looking for.
The pick up is 74.75 V at 115 V. For 120 V, PU is 62.29%.
Thanks to you all.
Yigo

 

[davidbeach]

Basic math...

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[che12345]

Dear Mr YIGO
1. I think I may had miss-understood your question.
My opinion is a 115V coil when connected to 115V, the pick-up voltage is at 74.75V . If you connect it to a 120V source, its pick-up voltage will be the same at 74.75V. For that matter, the pick-up voltage does NOT change irrespective of the over-voltage applied. However, if the applied voltage is below 74.75V, it would not pick-up at all.
2. However, a relay of the same design but rated 120V would pick-up probably at 0.65 x 120V = 78V. It is unlikely that the pick-up voltage would change to 0.62 x 120V = 74.4V .
Che Kuan Yau (Singapore)

 

[waross]

Probably the greatest factor affecting the pull-in voltage of a contactor is the air gap in the open position, not the rated voltage.


Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr waross
1. I have my reservation that Probably the greatest factor affecting [pull-in voltage] of a contactor is the air-gap that maintained in the open position. BTW it is the spring NOT the air-gap that maintained it in the open position, also plays a part.
2. Consider that most contactors need to change the coil, with different coil voltage say from 24---400V to suit the control voltage which may differ from the mains/source voltage. When we replace the original say a 24V coil to a say 400V coil, we neither carryout any adjustment to the air-gap nor replace the spring.
3. IEC 60947-4-1 specified that a contactor shall operate correctly between 85 to 110% of the rated control voltage. For this reason there are different coils, rated specifically for 24V,... 110V,... 380V...etc. They are NOT interchangeable.
4. I am of the opinion that the pick-up voltage is dependent on the voltage rating of the coil . A contactor pick-up voltage differs when it is installed with a 24V coil from that of a 400V; without any adjustment in the air-gap or the sprint.
5. There are coils with electronic interface that have very wide operation range e.g. 48...130V, 100...250V on 50/60Hz or 24V...60V, 48V...130V, 100V...250V on dc.
Che Kuan Yau (Singapore)

 

[waross]

The air gap is an inverse squared function while the spring tension is more linear.
Pull in as a percentage of the rated voltage.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!