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  • #16
    Originally posted by idiggplants View Post
    thats interesting. i didnt think a step down thing like that would be so cheap. is it efficient? i guess if we go 400w, we would also go with a second battery anyways, so we could put them in series.

    what if we put our limit at 3x 100w panels? the 20a could handle that... but could we run 3 in series? cause otherwise they would have to be in parallel if im not mistaken?
    The maximum DC input voltage is usually listed on the spec sheet for the CC. Usually the smaller PWM's do not have a very high DC volt input rating requiring you to wire the panels in parallel.

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    • #17
      It's definitely efficient enough to operate when you are actually using equipment. We have a shut off switch to shut it down when not at our cabin. That way it is not slowly draining the battery while running nothing at all. It is not perfectly efficient, but the way I look at it is that we gained by charging at 24v we lose some of that in the conversion process. Also you pretty much have to go higher than a 12v battery bank at a certain system size. Specs on the unit say it is 85% efficient, and has a 0.2 (2/10ths) of an amp for a no-load current draw. The no-load draw is why we installed a properly rated shut off switch between the battery bank and the 24v to 12v converter.

      As to the other question, the small charge controller would only handle your 300 watts at 24v. And yes you could run three 100 watt panels in series, I believe the max voltage to the charge controller will handle up to four 100 watt panels in series. (check the max input voltage in the manual to be sure).

      If I were in your situation, I would probably get the 40amp charge controller, and an extra panel if you want, and wire them in series. Then just keep everything 12v until you want to replace the current 12v battery. At that point you could go to 24v. The larger charge controller would give you the flexibility to do whatever you find works best. Starting with that would give you time to learn your needs, and avoid purchasing another battery until you actually need it.

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      • #18
        MPPT Size

        Amps = Panel Wattage / Battery Voltage.
        MSEE, PE

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        • #19
          ok thanks guys. i think im leaning towards the 40a version. that will allow us the most flexibility. i dont think a step down converter will work for us. too much loss.

          hopefully i can get a couple more people chiming in on experience with the renogy aka epsolar mppt controllers.

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          • #20
            Originally posted by idiggplants View Post
            ok thanks guys. i think im leaning towards the 40a version. that will allow us the most flexibility. i dont think a step down converter will work for us. too much loss.

            hopefully i can get a couple more people chiming in on experience with the renogy aka epsolar mppt controllers.
            Wait for what? A Renogy/Episolr 40 amp controller maximum input is:

            520 watts with 12 volt battery
            1040 watts with 24 volt battery.

            Do the math

            520 watts / 13 volts = 40 amps
            1040 watts / 26 volts = 40 amps

            Rad the manual page 10

            MSEE, PE

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            • #21
              Originally posted by Sunking View Post
              Wait for what? A Renogy/Episolr 40 amp controller maximum input is:

              Rad the manual page 10
              We are all reading files from your HDD Sorry buddy, couldn't resist!

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              • #22
                Originally posted by Sunking View Post
                Wait for what? A Renogy/Episolr 40 amp controller maximum input is:

                520 watts with 12 volt battery
                1040 watts with 24 volt battery.

                Do the math

                520 watts / 13 volts = 40 amps
                1040 watts / 26 volts = 40 amps

                Rad the manual page 10
                not looking for specifications at this point. looking for folks with good or bad experiences with, or opinions on, the controller.

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                • #23
                  Renogy 100w get free delivery, 1.30 perwatt. Bigger panels no free delivery. Also easier to deal with. Sturdier. Victron Blue solar mppt, excellent European company. 5 year warranty. Website will build confidence.

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