3 contactors not latching

Thread Starter

mztrordinary

Joined May 25, 2016
54
Hi dudes

i'm having a problem with the control of 3 3 phase contactors. The machine was running fine all day and then when it was stopped for 1 minute it wouldnt restart. On inspection i found that when the start button is pressed the contactors pull in for about one second and then they pull out again. It is like it is not latching. I have checked the circuit and found that things are where they should be in relation to continuity. So what i did was i took off the start push button switch and put on a rotary stay put switch. When i do this the machine runs and latches no problem and all the safetys (doors and e stops) still work too but i have to turn off the switch in order to stop the machine as the stop push button wont do it (obviously) when i try put the start push button back on the same thing happens it latches for 1 second then stops so i assume i am losing a leg of the latch circuit somewhere but im confused as it all runs on the rotary switch. Also when the stop button is pressed it pulls in a safety contactor in order for the rest of the circuit to run and when the machine is turned to position 3 and the stop button is pressed it works as a jog function for an external conveyor and this too is all working so am i on the right track assuming its the latch when its turned to position 1 and 2 which is normal operation


thanks guys

PS no drawings or plc access to this machine either
 

MaxHeadRoom

Joined Jul 18, 2013
28,576
It may all depend also on what external conditions are wired into the circuit, IOW the logic split between PLC and Hardwired logic! :rolleyes:
What PLC?
I guess you don't have a PLC monitor S/W?
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
28,576
What make of PLC?
You are obviously jumpering a latching contact by the sound of it?
Very difficult to trouble shoot with no documentation!
Max.
 

strantor

Joined Oct 3, 2010
6,781
Are the contactor coils directly powered from the PLC or is it a hardwired latch circuit?
(just cuz there's a PLC in there don't mean the PLC has anything to do with the contactors)
 

Jonplynch

Joined Jan 28, 2012
93
It's omron sysmac plc no software no monitor . When I force contactors in or give coils 24v it all works. I don't think I was getting 24 volts at the stop button before I gave up for the day
 

MaxHeadRoom

Joined Jul 18, 2013
28,576
Without documentation you need to do a little reverse engineering and draw it out as you go.
Start with the power source and follow through to the contactor coil.(s)
Max.
 
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