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  • What to buy?

    I am looking at getting solar for my caravan. I have followed the calculations in the sticky to get what I think I need to get.

    I have done the following calculations:

    Fridge - Engel - MT45FCP 40L Fridge/Freezer - 370w/24hrs @ 12v
    TV - 36w/hr x 6hrs = 216w @ 12v
    Computer - 12.5w/hr x 6hrs = 75w @ 12v

    So, total power required for 24hrs = 661w (I rounded up to 700w)

    This is what I ended with:

    Solar Isolation is 3.3

    Solar array 318w
    Battery 291ah @ 12v (5 days)

    I was thinking of 2 x 200w panels @ 12v to round up to 400w.

    I currently have a Plasmatronic PL40 charge controller that I got from a friend when they upgraded. It can use 24v panels to charge 12v batteries.

    My questions to the gurus: are my calculations correct? Can I use 24v panels? Which is better, 2 x 12v (lower AH) batteries or 2 x 6v batteries (higher AH).

    Thanks in advance

  • #2
    Originally posted by trash View Post
    I have done the following calculations:

    Fridge - Engel - MT45FCP 40L Fridge/Freezer - 370w/24hrs @ 12v
    TV - 36w/hr x 6hrs = 126w @ 12v
    Computer - 12.5w/hr x 6hrs = 75w @ 12v
    Are those sticker values? If so, that's fine, but might be overkill. For example, if the TV is a backlit lcd, then turning down the *backlight* as much as you can stand can save considerable power, especially if you are inside the caravan where it isn't too bright.

    The computer too might be the rating for running totally at maximum performance. You may save quite a bit in a power save mode.

    Normally a meter like the P3 International Kill-A-Watt meter is suggested to measure your wattage over time, but may not be available in Australia.

    How about a "Mains Power Meter" from Jaycar? Pretty sure you can get these in Australia. The MS6115 or MS6119 looks nice, although I have no experience with them.

    I'll let the other guys comment on the rest, but the meter might help you cut back your "normal" power consumption to the point you can use a smaller system, or have more autonomy.

    Comment


    • #3
      Originally posted by trash View Post
      I am looking at getting solar for my caravan. I have followed the calculations in the sticky to get what I think I need to get.

      I have done the following calculations:

      Fridge - Engel - MT45FCP 40L Fridge/Freezer - 370w/24hrs @ 12v
      TV - 36w/hr x 6hrs = 126w @ 12v
      Computer - 12.5w/hr x 6hrs = 75w @ 12v

      So, total power required for 24hrs = 571w (I rounded up to 600w)

      This is what I ended with:

      Solar Isolation is 3.3

      Solar array 272w
      Battery 250ah @ 12v (5 days)

      I was thinking of 2 x 150w panels @ 12v to round up to 300w.

      I currently have a Plasmatronic PL40 charge controller that I got from a friend when they upgraded. It can use 24v panels to charge 12v batteries.

      My questions to the gurus: are my calculations correct? Can I use a single 300w panel at 24v? Which is better, 1 x 250ah 12v battery or 2 x 6v.

      Thanks in advance
      In your TV calc, you have 6 * 36 = 126. I come up with 216.

      Comment


      • #4
        Originally posted by lkruper View Post
        In your TV calc, you have 6 * 36 = 126. I come up with 216.
        Thanks for that. I modified my OP to reflect this mistake.

        Comment


        • #5
          Originally posted by PNjunction View Post
          Are those sticker values? If so, that's fine, but might be overkill. For example, if the TV is a backlit lcd, then turning down the *backlight* as much as you can stand can save considerable power, especially if you are inside the caravan where it isn't too bright.

          The computer too might be the rating for running totally at maximum performance. You may save quite a bit in a power save mode.

          Normally a meter like the P3 International Kill-A-Watt meter is suggested to measure your wattage over time, but may not be available in Australia.

          How about a "Mains Power Meter" from Jaycar? Pretty sure you can get these in Australia. The MS6115 or MS6119 looks nice, although I have no experience with them.

          I'll let the other guys comment on the rest, but the meter might help you cut back your "normal" power consumption to the point you can use a smaller system, or have more autonomy.
          Thanks. Fridge power has been measured. TV and computer are working on max power ratings from the manual. TV would be turned off when not watching (not left in standby). Fridge obviously is the most important to keep going.

          Comment


          • #6
            Originally posted by trash View Post
            Can I use 24v panels? Which is better, 2 x 12v (lower AH) batteries or 2 x 6v batteries (higher AH).

            Thanks in advance
            You can use any panel(s) up to the maximum voltage and wattage ratings of the Charge controller, If it is a PWM controller you will lose 1/2 the power hooking a 24v panel to a 12v batt though, so keep that in mind, If it is a true MPPT controller then you will get good conversion to your battery bank. It is usually better to hook 2 6v batteries in series unless you can get a single 12v battery of proper AH for your needs.

            Comment


            • #7
              Originally posted by trash View Post
              Thanks for that. I modified my OP to reflect this mistake.
              So now I get:

              163 AH @ 24 volts or 324 @ 12 volts
              Panel size with MPPT 353, or 471 with PWM

              You ask about batteries, so I assume you don't have them yet. Where will you be storing the batteries? Flooded batteries are less expensive but require maintenance. AGMs cost 2X as much and last 1/2 as long. If you have a vented compartment in your RV with access for maintenance, flooded are a good choice. If you are keeping the batteries in your living compartment, most would use AGMs for safety. Getting one battery would simplify wiring but that battery will be heavy.

              As for charging, it is not always possible to place panels optimally on an RV or make sure it is parked where there is good sun. Will you be driving on a regular basis? If so, charging from your alternator will give you much more power than solar. Even so, if you don't want to kill your batteries, without another way to charge, you will need a generator or to regularly park with shore power. Will you be boon docking or have access to shore power? If you do not have access to shore power or cannot charge while driving from the alternator, you should over-size your solar.

              Comment


              • #8
                I have not purchased anything yet - everything is still at the planning stage. Will have access to power when staying at a caravan park. Primarily I am planning sizing for non-powered situations. I thought I would go maximum power on appliances for that reason.

                Comment


                • #9
                  Originally posted by trash View Post
                  I am looking at getting solar for my caravan. I have followed the calculations in the sticky to get what I think I need to get.

                  I have done the following calculations:

                  Fridge - Engel - MT45FCP 40L Fridge/Freezer - 370w/24hrs @ 12v
                  TV - 36w/hr x 6hrs = 216w @ 12v
                  Computer - 12.5w/hr x 6hrs = 75w @ 12v

                  So, total power required for 24hrs = 661w (I rounded up to 700w)
                  Just to be clear... "Power" is in Watts, and is an instantaneous measure of the Volts * Amps. "Energy" is in Watt-hours, and is the total power consumed over a period of time. For example, 100 W of instantaneous power (sic) consumed steadily for 1 hour = 100 Wh of energy.

                  With that in mind, I think what you are looking at is:

                  Fridge/Freezer: 15.4 W average power, 370 Wh daily
                  TV: 36 W power when on, 216 Wh daily
                  Computer: 12.5 W when on, 75 Wh daily (this seems low, unless you are talking about a mini-fanless type computer, but what monitor?)

                  The fridge's average power probably breaks down into periods of higher power consumption when it cycles, and lower power consumption between cycles. It would be good to know both, so that you can figure what the worst case power draw will be at any moment in time (with fridge cycling on, TV and laptop both running). Worst case power draw can matter because nameplate battery capacity is generally based on delivering steady power over 20 hours. If you have periods of a higher rate of consumption, the effective capacity may be somewhat less.
                  CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                  Comment


                  • #10
                    A suggestion

                    I happen to like https://handybobsolar.wordpress.com/ He is just a bit opinionated but gives the reasons and is very hard on folks who do not actually do the serious solar.
                    I agree with him Morningstar controllers are about as bullet proof as it gets. The New Trimetric 2030 looks good.

                    Comment


                    • #11
                      Originally posted by Shadow Catcher View Post
                      I happen to like https://handybobsolar.wordpress.com/ He is just a bit opinionated but gives the reasons and is very hard on folks who do not actually do the serious solar.
                      I agree with him Morningstar controllers are about as bullet proof as it gets. The New Trimetric 2030 looks good.
                      I have read bob. He is a hoot. But when I read him, I did not know anything. Now I know a little bit, enough to get into trouble. I should read him again.

                      Comment


                      • #12
                        The 12V power demand for your fridge is just what runs the 12V control board inside, the fridge actually runs on propane correct?
                        1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

                        Comment


                        • #13
                          Originally posted by thastinger View Post
                          The 12V power demand for your fridge is just what runs the 12V control board inside, the fridge actually runs on propane correct?
                          Engel is a high quality efficient AC/DC fridge/freezer using a Danfoss compressor. They don't make any propane models, as far as I know. I have read varying accounts of people getting an average of 2-5wh at 12v DC using them.

                          Comment


                          • #14
                            Originally posted by lkruper View Post
                            Engel is a high quality efficient AC/DC fridge/freezer using a Danfoss compressor. They don't make any propane models, as far as I know. I have read varying accounts of people getting an average of 2-5wh at 12v DC using them.
                            I see, thanks.
                            1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

                            Comment


                            • #15
                              Straight from the Engel website - DC Power Consumption: Variable from 0.5 to 2.7 AMPS Maximum. So max would be on first start up and possibly for a short period when the compressor kicks in.

                              So in short, 6w at 12v and max 32w at 12v.

                              Comment

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