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internal blown fuse

Created by: byrono at: 5/13/2016 4:08 PM (4 Replies)

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5/13/2016 4:08 PM	Rate (0)
byrono Posts: 2 Rating: (0)	I have an S7-1200 CPU1215C DC/DC/RLY that is installed in a system. The PLC recently suffered a blown internal fuse on the power supply board within (see attached image of part). The fuse is open, but there is no physical damage apparent to the unit other than the open fuse measured with a meter. My customer is asking what scenarios could potentially cause this in the hopes of preventing it from occurring again. Where could I begin to understand what the cause of the failure might have been? Could this be simply from a DC voltage spike on the incoming power to the unit and if so, how high of a spike could cause a blown fuse (it's nominally at 24VDC)? Attachment siemens fuse.png (384 Downloads)
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5/14/2016 11:16 AM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	Usually, not connecting the 24VDC rated PLC on the AC mains helps a lot. Look if the varistor is blown also, then cut it away and make a short to the fuse and you have a PLC still functioning for test, not for field use anymore.

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5/14/2016 3:40 PM	Rate (0)
Ste39 Platinum Member Joined: 1/21/2013 Last visit: 11/20/2024 Posts: 4620 Rating: (709)	byrono I have an S7-1200 CPU1215C DC/DC/RLY that is installed in a system. The PLC recently suffered a blown internal fuse on the power supply board within (see attached image of part). The fuse is open, but there is no physical damage apparent to the unit other than the open fuse measured with a meter. My customer is asking what scenarios could potentially cause this in the hopes of preventing it from occurring again. Where could I begin to understand what the cause of the failure might have been? Could this be simply from a DC voltage spike on the incoming power to the unit and if so, how high of a spike could cause a blown fuse (it's nominally at 24VDC)? Dear byrono, sorry if I intruding, I have never opened a CPU1200 but the specifications of the CPU 1215C says if you look belowon the tab Timers, Counters and code blocks supported by the CPU 1215C in Table 3 "Power supply" says: Internal fuse, not user replaceable 3A 250V, slow blow, then I wonder: are you sure it is the right CPU and not something else? SIMATIC S7 S7-1200 Programmable controller I think it's more a resettable fuse

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5/16/2016 2:53 PM	Rate (0)
byrono Posts: 2 Rating: (0)	The PLC was installed in a working system. The system voltage was 24VDC and not an AC voltage. The unit had been in operation vor approx. 3 months when the PLC failed. I am also certain I'm using the correct PLC. While I completely understand that the fuse is NOT user replaceable, I am trying to understand what to review in the system that could have caused this to be damaged. I want to make sure that the customer's confidence level isn't affected by this outage.
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5/16/2016 4:03 PM	Rate (1)
William_B Posts: 5225 Rating: (1198)	Hi Byrono, Sorry to hear about the trouble you are having. Many factors can lead to failures - I assume you have a good 24Vdc power supply and is guarded against excessive EMF influences. byrono .. I am trying to understand what to review in the system that could have caused this to be damaged. I want to make sure that the customer's confidence level isn't affected by this outage. Seeing that this is a forum for Siemens industrial equipment users, I doubt you will get the clear answer you hope for. To speak directly to Siemens at - SIEMENS SUPPORT. In our age of mass production, this kind of occurrence is unfortunately not unheard of. The internal tracks of the PC board may have a crack somewhere that contributed to the failure - for example. I have had such problems before with Siemens.. but to be fair I have had such issue with Japanese and USA brands too. Normally there is a 6 month or so warranty on equipment such as this.. find out if you can claim. Maybe you can ask them to investigate the cause (autopsy) and make a report to you with recommendations. Please feel welcome to let us know if other avenues brought a better result. w
William_B Posts: 5225 Rating: (1198)
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