Uni III Blowing Fuses

Working on some electrical gremlins on a Uni III that is blowing its 5amp fuses (larger ones). When in manual mode, the carriage will go to the end of the bed with no problem but will not return and it appears to blow the fuses once at the end of the bed. Should I be looking at replacing the switches towards the end of the bed or is this likely a motor issue? Hoping the gurus can point me in a direction. Thanks uni.iiip

11 thoughts on “Uni III Blowing Fuses

  1. Paul Moxon, Moderator - January 13, 2021

    Excellent. Please post a follow-up with photos or video.

  2. ajmasthay - January 13, 2021

    Update on the Uni III. We went ahead and tried running a small edition without the third microswitch in place. Carriage ran fine for the first few cycles, no slamming, but eventually there was a lot of chattering in one if not multiple relays. Ive decided enough is enough and will be completely retrofitting the electronics with the help of Vladimir Schuster. Wish me luck!

  3. ajmasthay - January 2, 2021

    I guess by ruling out the microswitch it has to be the relay, no? The good news is I have spare relays in my parts stash, the bad news is I’ve yet to have to dive into the electrical bits on one of these presses and honestly have no idea what Im doing. Is there any sort of tutorial out there on determining which relay controls what and how to go about replacing one? Is there a way to “test” if a relay is functioning correctly?

  4. Paul Moxon, Moderator - January 2, 2021

    Kevin’s correct, the third microswitch slows the carriage on the forward travel. Many universals have the microswitches numbered 1, 3, 4, 2. If you swap or replace that switch then it may be the relay.

  5. kpmartin - January 2, 2021

    I’m not specifically familiar with this motorized press, my previous comment was just my general diagnostic methods at work trying to answer the question “why doesn’t the fuse blow when you manually operate the switches?” and the answer would seem to be that it is because you aren’t operating them the same way they would operate automatically.

    My belief is that the purpose of the third switch is to de-energize the motor before the end of the stroke so the carriage can slow down before it hits the stop and/or the motor is energized in reverse. The system relies on momentum to carry the carriage from the third switch to the fourth so if you’re running the motor too slow the carriage will stall between the 3rd and 4th switch positions.

    I’m not sure what would happen if you remove the 3rd switch; probably the motor would slam from forward into reverse when the 4th switch is reached, which would be rough on the motor as well as on the electrical and drive systems. You certainly would not want to leave it running this way long term.

    Both switches do something (that is, they have some effect) so I think they are fine. More likely it is a relay somewhere with stuck contacts, or perhaps an internal connection has worked itself loose. That’s where the wiring diagram would help as it would let you analyze which components could contain the fault that causes the fuse to blow.

  6. ajmasthay - December 31, 2020

    Thanks for the response Kpmartin, I did not try actuating both at the same time which I believe the carriage does when operating. However, the bar which hits the microswitch arms doesn’t make it far enough along to even hit the 4th switch.

    It was suggested to me that I remove the 3rd microswitch from the side of the press (let it dangle) and run the press. We did this and it worked fine, no issues in either manual or cycle. I also tested the 3rd microswitch with a multimeter and it appears to be fine. Does this narrow it down to a wire or relay issue? I should mention this press was working perfectly when I received it so I don’t think the wiring is “wrong”. Video os the test is at https://youtu.be/ZbABolje7n0

  7. kpmartin - December 30, 2020

    So it doesn’t blow the fuses until the second (reverse) microswitch is tripped? Is the first (stop) one still actuated at that point? In your manual test did you try actuating the second switch while the first one is still actuated?

    I don’t know the shape of the carriage cam that actuates these, whether it can actuate both at once or not. But that would be the only way that would explain why your manual switch applications did not blow the fuses. I would need to see the wiring diagram before I could take a guess at why actuating both switches blows the fuse (assuming that is indeed what is happening).

  8. ajmasthay - December 29, 2020

    I put a video of us testing the microswitches on YouTube, the link is https://youtu.be/-PK8P9sti-c

  9. ajmasthay - December 29, 2020

    Little more testing with interesting results. If I send the carriage down and then manually push the second to the last microswitch the carriage will stop, if I push the last microswitch it will send the carriage back. We repeated this test multiple times and everything seems fine. Once I send the carriage all the way down though, the bar on the side will hit the first switch and stop – the carriage will not move in either direction and the 5amp fuses appear to blow. The bar never makes it far enough down to actuate the last switch at the end of the bed.

  10. ajmasthay - December 29, 2020

    Just tested again with fresh fuses. With the press in cycle the carriage goes down to the end of the bed and stops, does not return. Switched to manual and same, no response back or forward. Upon checking the two fuses both are blown.

  11. Paul Moxon, Moderator - December 28, 2020

    I don’t think it is the micro switch. It could be the reverse relay Does the carriage return in run and cycle?

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