motor softstarter troubleshoot
motor softstarter troubleshoot
(OP)
Hi all. I have been working with a softstarter fault issue on my company's equipment for over a month now. The softstart is an Allen-Bradley SMC-3, and the fault is four-flash Phase-Loss/Open Load. I have initiated one fix so far, which initially reduced the faults entirely. What I suspected initially was that the signal from the reverser [5MREV] control block, which ran to both the contactor [5M] coil and the sfst START signal, caused the sfst to finish its prechecks in some machines/instances before the contactor had fully closed, thus faulting a Phase Loss/Open Load. I put the signals and power up on a scope on a non-faulting piece of equipment in my shop and proved this was possible. It took 5M 68ms to close, and A-B specs say the initial checks are done in ~31ms. IDK why this wouldn't happen every time.
The first solution I implemented was then to wire the sfst START signal through the AUX contact of 5M. This delayed the sfst START signal by ~69ms. I changed wiring on 13 machines in two facilities, and all the faults went away -- at least initially. One facility has since reported two of the same faults again in one month's time. This machine used to fault 3-5 times per day before the fix.
I have attached drawings. Sheet 7 is the Power circuit, Sheet 13 is the Control circuit, Rev A before my fix and Rev B after.
My next step is to change out the contactor and reverser and to set up the scope on the troubled machine. I think I need to go back with more than this. What do you all think?
The first solution I implemented was then to wire the sfst START signal through the AUX contact of 5M. This delayed the sfst START signal by ~69ms. I changed wiring on 13 machines in two facilities, and all the faults went away -- at least initially. One facility has since reported two of the same faults again in one month's time. This machine used to fault 3-5 times per day before the fix.
I have attached drawings. Sheet 7 is the Power circuit, Sheet 13 is the Control circuit, Rev A before my fix and Rev B after.
My next step is to change out the contactor and reverser and to set up the scope on the troubled machine. I think I need to go back with more than this. What do you all think?





RE: motor softstarter troubleshoot
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: motor softstarter troubleshoot
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: motor softstarter troubleshoot
RE: motor softstarter troubleshoot
wire 22 is 24VDC common
wire 31 is essentially 21 after the master control relay
wire 32 is 31 after customer interlock relay.
RE: motor softstarter troubleshoot
Here, for one, is the sfst sequence of operation, attached.
RE: motor softstarter troubleshoot
You are using 24VDC control, but have a number of contactor coils and a lot of control circuit interlocking going on, including several to external limit switches, meaning distance. You may be suffering from voltage drop when that final contactor pulls in. Maybe not much or for vary long, but just enought to push it below the minimum for the SMC-3 power (A1-A2) at that critical moment. You can test it by temporarily bypassing (with the proper precautions) all other interlocks etc, and just powering 5M and the SFST. If the problem goes away, you at least know where to start looking.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: motor softstarter troubleshoot
RE: motor softstarter troubleshoot
Keith Cress
kcress - http://www.flaminsystems.com
RE: motor softstarter troubleshoot
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: motor softstarter troubleshoot
RE: motor softstarter troubleshoot
I have just returned from the job site. I waited for two days with test equipment set up. Finally a fault happened. My hand happened to be on the joystick at the time. As I Extended the machine, it began to drag for maybe 2 seconds, before stalling and faulting. Same fault: Phase Loss/Open Load. I came back and reread squeeky's comment. The equipment is less than a year old. I was not reversing at the time. My first guess is that the brake was sticking.
What do you all think?
QGeek