Running a microcontroller in car - power supply aspects

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  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 30963
    • Albion

    #161
    Re: Running a microcontroller in car - power supply aspects

    the resistance will be in the datasheet

    Comment

    • Dannyx
      CertifiedAxhole
      • Aug 2016
      • 3912
      • Romania

      #162
      Re: Running a microcontroller in car - power supply aspects

      Originally posted by stj
      the resistance will be in the datasheet
      Right, though that's assuming there IS a datasheet for these things
      Wattevah...

      Comment

      • Dannyx
        CertifiedAxhole
        • Aug 2016
        • 3912
        • Romania

        #163
        Re: Running a microcontroller in car - power supply aspects

        Yes, turns out I was almost right: the specs give a 27ohm resistance.
        Wattevah...

        Comment

        • stj
          Great Sage 齊天大聖
          • Dec 2009
          • 30963
          • Albion

          #164
          Re: Running a microcontroller in car - power supply aspects

          nice parts, i like the way the contacts have low current pcb pins too.
          you could use the mcu to detect relay failure or motor/wiring issues through those pins!

          Comment

          • Dannyx
            CertifiedAxhole
            • Aug 2016
            • 3912
            • Romania

            #165
            Re: Running a microcontroller in car - power supply aspects

            Kinda running low on pins on the Mini TBH, though not a bad idea in the long run.
            Wattevah...

            Comment

            • redwire
              Badcaps Legend
              • Dec 2010
              • 3900
              • Canada

              #166
              Re: Running a microcontroller in car - power supply aspects

              You can use a resistor to lower the coil voltage from 12V to 5V. Like 47R and dissipating ~1.5W, regardless if a resistor or vreg or zener etc. the heat is made by something.
              A relay coil is mostly a resistor anyway, just wirewound with copper. They need a constant amount of power (not current/voltage) to work, so a 5V coil and 12V coil are the same power.
              If the relays are only on for a few seconds, then 1W resistors would work. Just takes up space.

              Comment

              • eccerr0r
                Solder Sloth
                • Nov 2012
                • 8688
                • USA

                #167
                Re: Running a microcontroller in car - power supply aspects

                put a reverse biased 7V zener diode in series
                But yeah unfortunately damage's done, should have got the 12V units. Resistor is cheaper than zener, but you may need to calculate an appropriate value. And you can't get away with power consumption, it'll be significant, most of the relays I've seen when an option is given, the power consumption is the same when they're run at their rated voltages, meaning if you have to run on higher voltages, it will use more power overall.

                ... unless you PWM the input and filter it... HMM... heh heh heh...

                Comment

                • stj
                  Great Sage 齊天大聖
                  • Dec 2009
                  • 30963
                  • Albion

                  #168
                  Re: Running a microcontroller in car - power supply aspects

                  it's not an issue, the buck convertor can easily drive the arduino and the relays.

                  Comment

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