Franken system - AC watts vs DC watts

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  • Camp guy
    Junior Member
    • Apr 2014
    • 2
    #1

    Franken system - AC watts vs DC watts

    I have taken over running a youth wilderness camp in northern Canada. It is off the grid and the solar power is a bit of a Franken-system that has been built over time. For lighting we are running 110v AC 13W compact florescent bulbs through the inverter. Somehow this seem like a poor use of power to me. I am thinking of switching to 12v DC led strip lighting. I'm not quite sure how to calculate this to find out what my power saving would be. Is there an easy way to calculate what the 12V DC draw in Watts is on my battery bank in order to run a 110v AC 13W compact florescent bulbs through the inverter?

    Just trying to figure out how stretch my power and get the most lumens out of my DC Watts.
    Tags: None
    • Shockah
      Solar Fanatic
      • Nov 2013
      • 569
      #2
      AC or DC, watts are watts.

      However, you are losing efficiency (about 20%) through that inverter.

      Replace the 120vac CFLs with 12vdc E27 bulbs.(AFTER YOU'VE CONVERTED VOLTAGE INPUT TO 12VDC)
      I've used 12vdc LEDs, 3w 5w and 6w that put out a decent amount of light.
      [CENTER]SunLight @ Night[/CENTER]

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        • Camp guy
          Junior Member
          • Apr 2014
          • 2
          #3
          So if I had a 12v DC 13w bulb and a 120v AC 13 W bulb they would both consume the same amount of battery reserve except for the extra 20% that the inverter is using?

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            • Shockah
              Solar Fanatic
              • Nov 2013
              • 569
              #4
              Originally posted by Camp guy
              So if I had a 12v DC 13w bulb and a 120v AC 13 W bulb they would both consume the same amount of battery reserve except for the extra 20% that the inverter is using?
              Correct.

              ... and your inverter is consuming watts at idle, even when the lights are all off... unless you are switching the inverter off.
              [CENTER]SunLight @ Night[/CENTER]

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                • ButchDeal
                  Solar Fanatic
                  • Apr 2014
                  • 3802
                  #5
                  Originally posted by Camp guy
                  So if I had a 12v DC 13w bulb and a 120v AC 13 W bulb they would both consume the same amount of battery reserve except for the extra 20% that the inverter is using?
                  You would also have some issues with DC loss on long wire runs. Mostly mention this as you said it was a summer camp, and I maintained a summer camp way back, there can be some long power line runs.
                  you could have a simpler time of changing lights to LED A/C. You wouldn't have much to change with that and though you still have some inverter losses, you wouldn't have to worry about wire lengths and DC loss.
                  OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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                    • Shockah
                      Solar Fanatic
                      • Nov 2013
                      • 569
                      #6
                      <debate>

                      Originally posted by ButchDeal
                      You would also have some issues with DC loss on long wire runs. Mostly mention this as you said it was a summer camp, and I maintained a summer camp way back, there can be some long power line runs.
                      Good point about long wire runs producing a voltage drop. Keep your voltage drop within acceptable range (3%).
                      No matter the amount of voltage drop your lights still work without consuming more watts.
                      I have 12 volt LEDs that work just as well with 10v power.

                      Originally posted by ButchDeal
                      you could have a simpler time of changing lights to LED A/C. You wouldn't have much to change with that and though you still have some inverter losses, you wouldn't have to worry about wire lengths and DC loss.
                      All good until your inverter takes a hike. (IMHO, inverters are the weakest link in off-grid systems).
                      If you eliminate the inverter, you lower the risk of a black out.

                      Other than avoiding voltage drop on ridiculously long runs or powering up Halogens/Halides,
                      using an inverter for off-grid CFL/LED lighting is simply a waste.


                      </debate>
                      [CENTER]SunLight @ Night[/CENTER]

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