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    • nikhillemosnikhillemos
      Participant
      December 9, 2024 at 5:01 am
      Post count: 7
      #19203

      Hi team.

      I’m facing a voltage drop issue on the HSO of the FCGs when I am turning the LSOs on on the VCU I have. I have compared the Supply Voltage(VBATT) and HSO output voltage when the LSOs are turned on and noticed a large difference. Point to note, this seems to be specific to PWM signals given to the LSOs.

      Description of the Setup: I have the FCG with 16 of its LSOs dedicated to driving solenoids each rated at 8W each. The solenoids tend to heat up if left on continuously , so in software we initially trigger the solenoids with a 100% duty cycle signal and once the solenoid is on we give it a 30% duty cycle to keep it on without too much of power draw. The PWM frequency is set at 2kHz.

      On the HSO bank we have a enable pin connected to HSO7. This is the pin where I am measuring the voltage drops.

      The voltage drops slowly at first as we turn on the first 3 solenoids, drops from 26.11V to 26.10V. By the time we switch the 6th solenoid, we drop to a voltage of 24.56V. Supply voltage at the same time is 25.87V

      For the same test, if the allow the VCU to maintain a duty cycle of 100%, the HSO output follows the battery voltage.

      We also tried the same at 50% duty cycle and had even more drastic drop in voltage, where after switching the 6th solenoid, the HSO voltage was noted at around 12V.

      Our previous VCU faced the same issue initially and then the High side bank stopped working. HSO 1-10 are no longer operational on that VCU.

      Please advise on what could be the issue here.

      Thanks,
      Nikhil

    • AmirFAmirF
      Moderator
      December 10, 2024 at 9:29 am
      Post count: 25
      #19205

      Hi Nikhil,

      Thanks for the detailed description of the issue.
      I still have some questions regarding the issues happening. The answer will clear up the problem for us.
      You stated that the LSOs are driving the solenoids. How much is the total current draw for the LSOs from all the LSOs?
      If the overall current draw from all LSOs is 20A or more, can you measure the voltage difference between the GND_IN pin(J2-5/6) and the big GND pads on the PCB, or the enclosure itself if case is closed, when the FCG is in a faulty state?
      Are the HSOs also driving inductive loads? Do you have an estimation of the inductance?
      Have you utilized external flyback diodes in your setup?

    • nikhillemosnikhillemos
      Participant
      December 11, 2024 at 9:43 am
      Post count: 7
      #19208

      Hi Amir,

      Thanks for the quick reply. To answer your questions, the solenoids are 8W each running ON A 24v power supply. We measured the current on a couple of the solenoids at the when we were running the test and found it to be around 120mA each when PWM is on. During our testing we only turned on all the solenoids a couple of times. Most of the time we turn on 6 solenoids at a time. So the max current running through the LSOs would come out to around 2A.

      The HSOs are not driving any of the solenoids in the current configuration. Previously they were driving half the solenoids, but we noticed the same issue of the voltage dropping after activating multiple solenoids and this would cause issues with the activation of subsequent solenoids. They would either not turn on or would chatter. This was why we shifted all the solenoids to the LSOs

      We have used external flyback diodes on all the solenoid LSOs.

      Considering that even the calculated value for the current is around 5.5A, would you still like me to run the check you have mentioned? I do not have an estimate for the inductance right now but I’ll update the post once I get that.

      Thanks,
      Nikhil

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