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DC circuit question

  • 20-12-2021 12:06PM
    #1
    water-man
    Registered Users, Registered Users 2 Posts: 285 ✭✭


    Hello,

    I'm playing with a simple 24V DC circuit and some pneumatic valves, relays etc. I have 2 car batteries in series, a small control panel with a little PLC and then a harness going to my valves.

    It was working fine however then all of a sudden started behaving strange.

    I discovered inside my panel when I key'd it on - all the 0V line had 24V on then and the output pins on the PLC had 5 to 20V depending on the pins and the valves where being activated! Found my 0V lines in my panel terminals where not connected to my neg side of the battery.

    (The 0V side of the valves where connected directly to the battery negative not to the panel 0V terminals and this is why they where operating as they had a dedicated 0V path and thus when they got voltage from the PLC activated)

    Once I connected the 0V terminals to the incoming battery negative inside the panel it corrected the problem and all issues gone.

    However, what I struggling & would like to understand is - how did it work at all if the 0V lines where not connected to the battery negative and only after a few hours start to mis-behave?

    Thoughts?



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