24Vac Contactor latching problem.

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RHeTTRoNiCS

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Hello Guys...we have a motor driver equipement. The input ac line link into step down transformer 24Vac...This 24Vac is then feed to the contactor coil. But the problem is the contactor is not engaging. However, when contactor is removed we can read 24Vac from the connector. Thus, we tried to energized manually the contactor by different AC source but it's working. Any idea what is the problem??? Thanks.
 

Probably you have voltage drop, and contactor coil dont have enough energy to work.


Best regards,
Peter
 
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    FvM

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You don't report significant measurements.

Usually you'll measure the voltage across the contactor coil when the external voltage is supplied. If it's not suffcient, trace the connection up to the transformer to find out where's the discontinuity or unwanted voltage drop.
 
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    tpetar

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Hello folks, got the same issue. Most likely what is the cause of this voltage drop?
 

check if your contactor can work with the voltage and current you are providing it with
 


If you read 24V when the contactor is not connected, then it means the voltage is dropping when you connect the contactor. This is because the step down transformer is not able to drive the contactor (not able to source enough current) To confirm that,Check the voltage across the coil when the contactor is connected.
 

The voltage is Zero across the coil when connected and with the power source on...Done tracing also with all connections but all ok. Should it be the problem is the transformer? Since the contactor works through different ac source...thanks.
 

RHeTTRoNiCS said:
The voltage is Zero across the coil when connected and with the power source on...Done tracing also with all connections but all ok. Should it be the problem is the transformer? Since the contactor works through different ac source...thanks.
Click to expand...

Replace transformer. See contactor datasheet, what current is needed for coil.


Best regards,
Peter
 
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    FvM

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Done tracing also with all connections but all ok. Should it be the problem is the transformer?
Click to expand...
You won't need to ask if you have measured the transformer voltage in unloaded and loaded case.

Besides checking for wiring continuity, you'll also check for shorts.
 
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    tpetar

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charu2539211 said:
check if your contactor can work with the voltage and current you are providing it with
Click to expand...

hello charu, actually the circuit was previously working, now i tried checking the voltage across the transformer (the one that feeds voltage to the contactor) and the contactor itself. at the moment i disengage the contactor supply voltage connection, its reading is 24vac and same goes to the transformer is giving 24vac. but when i engage the supply of the contactor the reading becomes 0vac but the transformer is still producing 24vac read out.

on the other hand, i already tested the contactor with a different voltage supply and its working.
 

when i engage the supply of the contactor the reading becomes 0vac but the transformer is still producing 24vac read out.
Click to expand...
So there's a discontinuity between transformer and the terminals where you measured voltage. I guess it's normal behaviour, but you didn't understand the circuit yet, e.g. a blown fuse, a tripped overload relays ...
 
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    tpetar

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FvM said:
So there's a discontinuity between transformer and the terminals where you measured voltage. I guess it's normal behaviour, but you didn't understand the circuit yet, e.g. a blown fuse, a tripped overload relays ...
Click to expand...

there was a motor overload relay in between the contactor and the transformer


i'd made a voltage check on two locations at the same time 1) between A & B, and 2) between D & C. the moment i disengage the contactor connection at 1) and 2) both measured 24vac, the moment i engage the contactor 1) got 24vac and 2) becomes zero,

you think i measured in the wrong point? thanks
 

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