# AC Crane Contactor Issue



## Jesseduvuvei (Dec 26, 2013)

Hi all, recently had a issue on a wound rotor crane where the hoist would cut out with a load on it while going up, intermittently though. Found the issue to be the Hoist Raise contactor wanting to chatter pretty badly on the times that it would cut out. It would only do this when the operator would attempt to go straight across the line to 3A contactor (final step.) Concluded that the reason it was chattering was due to the fact that in between 2A and 3A there was supposed to be a timer to limit 3A from coming right into the circuit and causing a large amount of inrush current (timer was still on the crane but somebody decided to take it out of the circuit). So my question is, why would the final acceleration contactor coming in too soon be causing the directional (only the hoisting contactor) to chatter?


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## backstay (Feb 3, 2011)

My guess with so little information is voltage drop.


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## telsa (May 22, 2015)

2nd guess: swinging back-EMF.


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## sparkiez (Aug 1, 2015)

Do you have a schematic to the circuit? A contactor chattering could be from a few things. I would think that the timer being there is more for interlock, but with a schematic we could do a better job of checking it out.


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## Big John (May 23, 2010)

backstay said:


> My guess with so little information is voltage drop.


Yep. Would explain why it only happened going up: The crane is under the most load and is drawing the most current.


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## PokeySmokey (Nov 14, 2017)

I support voltage drop which could be made worse if the coil in contactor 3A is weak (beginning to fail).

Also check for loose connection(s) in the circuit for Contactor 3A.

If the crane has an electric brake, make sure it stays released when contactor 3A is energized.


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## Chrismcd (Apr 9, 2014)

I would check the break contractor, as well as the connections before and at the coil often on a crane the vibration will cause a loose connection for a intermittent loss of voltage. Could also be a issue with the switch on the hoist. Is it a two speed motor or a wound rotor motor as if it has resistor bank check the connections there first. 


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## frenchelectrican (Mar 15, 2007)

Jesseduvuvei said:


> Hi all, recently had a issue on a wound rotor crane where the hoist would cut out with a load on it while going up, intermittently though. Found the issue to be the Hoist Raise contactor wanting to chatter pretty badly on the times that it would cut out. It would only do this when the operator would attempt to go straight across the line to 3A contactor (final step.) Concluded that the reason it was chattering was due to the fact that in between 2A and 3A there was supposed to be a timer to limit 3A from coming right into the circuit and causing a large amount of inrush current (timer was still on the crane but somebody decided to take it out of the circuit). So my question is, why would the final acceleration contactor coming in too soon be causing the directional (only the hoisting contactor) to chatter?


Did you check the connection on crane track tolley ? I know when you mention wound rotor motor I have a feeling this is on the track trolley crane set up.

First thing I would check the concat on buss bar fingers to make sure they are good.

Did you check the contractor to make sure the concant is good and the contractor coil is good ( verify the voltage to make sure it not bouncing all over the place ) 

I would check the supply voltage at contractor when you are in hosting mode and check the brake on motor to make sure it is disengaged when it is running. 

Just be aware there is more than one set banks of contractors due you have wound rotor motor in there so there is two half of it ., one half for power and other half for wound rotor for shuntting coils and shorting contractor ( only in high speed )


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## Tonedeaf (Nov 26, 2012)

I would check all brushed connections first, trolley, span wire etc, before you start pulling **** apart. 

Send a pic


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## JRaef (Mar 23, 2009)

Wound Rotor motors have different torque/speed curves depending on the amount of external resistance put in the circuit; the higher the resistance, the lower the torque and thus the speed. That's what those contactors do, they short out the resistors in steps to slowly increase the torque. Maximum torque is delivered with zero external resistance, but if done too soon, meaning when slip is extremely high, the current surge can be 1000% of FLA and cause damage to the control equipment and an extreme voltage drop. That's why the timer was there, to allow the motor speed to increase and avoid that high slip / high current surge. 

Most likely someone was trying to lift too much load and at the lower speed, the lower torque was allowing the motor to stall, so they got rid of that timer to get max torque. But now you are paying the price for that... 

There is no free lunch.


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## Jesseduvuvei (Dec 26, 2013)

Thanks all for the replies. I knew that this issue was due to the rotor being shorted way too soon, just wasn?t sure why it was causing the contactor to chatter. Should?ve considered voltage drop, just slipped my mind. Although thinking back on it now it did cause all of the HID lights in the bay to dim considerably when it happened


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## Chrismcd (Apr 9, 2014)

I don’t think shorting the rotor that early should be a issue I’ve shorted some pretty large motors rotors to have them run when a resistor bank was fried etc. I’d still figure it’s a loose connection at the control side or a issue with the contactor I would change the contactor and chase the control for that to make sure it’s not a bad relay etc outputting to the lift high speed. Is it pendent or radio control? 


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## Jesseduvuvei (Dec 26, 2013)

It is radio control, and we checked all checkable connections (could possibly be a weak coil) checked back today and putting the timer back into the circuit has solved the problem, so my conclusion is the large inrush caused a voltage drop


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## Chrismcd (Apr 9, 2014)

I’ve had many radio control relays act like this then they will be fine for abit and it will happen again if it comes back swap the relays on the receiver. What radio control system are you using ? 


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## Jesseduvuvei (Dec 26, 2013)

We are using Cervis


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## Tshock (May 24, 2021)

Jesseduvuvei said:


> Hi all, recently had a issue on a wound rotor crane where the hoist would cut out with a load on it while going up, intermittently though. Found the issue to be the Hoist Raise contactor wanting to chatter pretty badly on the times that it would cut out. It would only do this when the operator would attempt to go straight across the line to 3A contactor (final step.) Concluded that the reason it was chattering was due to the fact that in between 2A and 3A there was supposed to be a timer to limit 3A from coming right into the circuit and causing a large amount of inrush current (timer was still on the crane but somebody decided to take it out of the circuit). So my question is, why would the final acceleration contactor coming in too soon be causing the directional (only the hoisting contactor) to chatter?


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## Tshock (May 24, 2021)

Check the shading pole on the contactor, for open


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## John Valdes (May 17, 2007)

Tshock said:


> Check the shading pole on the contactor, for open


This thread is 4 years old.


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