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12v-10amps or 24v-5amps - which will charge faster

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  • 12v-10amps or 24v-5amps - which will charge faster

    Hi, I'm just a newbie in solar power, please anyone explain me which is better and charge the battery faster, regardless of cost implication in wire size.

    Sample panel of 2 each with size 12 volts, 100 watts - 5 amps
    Using mppt charge controller and battery of 12 volts.

    scenario 1 - in parallel - 12 volts, 200 watts, 10 amps

    scenario 2 - in series - 24 volts, 100 watts, 5 amps

  • #2
    Originally posted by noelana View Post
    Hi, I'm just a newbie in solar power, please anyone explain me which is better and charge the battery faster, regardless of cost implication in wire size.

    Sample panel of 2 each with size 12 volts, 100 watts - 5 amps
    Using mppt charge controller and battery of 12 volts.

    scenario 1 - in parallel - 12 volts, 200 watts, 10 amps

    scenario 2 - in series - 24 volts, 100 watts, 5 amps
    The watts will be the same either way you connect them.

    5a X 24v = 120 watts
    10a X 12v = 120 watts

    charging time should be similar other than the fact that 24v would be slightly more efficient (less heat created) and may charge a little quicker.

    Comment


    • #3
      Originally posted by noelana View Post
      Hi, I'm just a newbie in solar power, please anyone explain me which is better and charge the battery faster, regardless of cost implication in wire size.

      Sample panel of 2 each with size 12 volts, 100 watts - 5 amps
      Using mppt charge controller and battery of 12 volts.

      scenario 1 - in parallel - 12 volts, 200 watts, 10 amps

      scenario 2 - in series - 24 volts, 100 watts, 5 amps
      200 watts = 200 watts on paper.

      However if you use a MPPT controller the charge current @ 12 volts = 200 watts / 12 volts = 16.6 amps. You would wire the panels in series even on a 12 volt battery. For 24 volt the the charge current would be 200 watts / 24 volts = 8.3 amps.

      Now with that said if you were to use a PWM controller is the example you really gave. If you were to use a PWM controller you are forced to wire the panels in parallel for the 12 volt battery and current would be 10 amps or roughly 120 watts with 200 watts input. With PWM controller Current In = Current Out. With MPPT Current Out = Power In / Battery Voltage. Huge difference.
      MSEE, PE

      Comment


      • #4
        My manual for my Trace TC60 states the Bulk charge at 14.4vdc factory default for FLA batteries and is adjustable to 16.8vdc according to my install manual. That is a little more than 12vdc, and hardly calls for a MPPT charge controller if your panel has a VMP of only 17vdc. Am I missing something? Are you saying when the battery is in a discharged state that the panel is acting as a current source and can only provide max current to the batteries at the batteries discharged voltage state (12vdc) and that the bulk setpoint is the charged voltage level at which the controller switches to absorb?
        Last edited by Saggys; 06-06-2014, 11:27 PM. Reason: added question

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        • #5
          PV panels ARE current sources.
          Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
          || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
          || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

          solar: http://tinyurl.com/LMR-Solar
          gen: http://tinyurl.com/LMR-Lister

          Comment


          • #6
            Originally posted by Saggys View Post
            My manual for my Trace TC60 states the Bulk charge at 14.4vdc factory default for FLA batteries and is adjustable to 16.8vdc according to my install manual. That is a little more than 12vdc, and hardly calls for a MPPT charge controller if your panel has a VMP of only 17vdc. Am I missing something? Are you saying when the battery is in a discharged state that the panel is acting as a current source and can only provide max current to the batteries at the batteries discharged voltage state (12vdc) and that the bulk setpoint is the charged voltage level at which the controller switches to absorb?
            What you do not understand is Bulk, Absorb, and float are only set points in which the controller switches from one state to another. Bulk is setting to run the controller in a Constant Current Mode, and the panels can only produce X amount of current. Iv the case of a PWM controller Input Current = Output Current. So if you have 170 watt 12 volt battery panels all you are going to get is 10 amps at best.

            Now if your 12 volt battery is at 50% State of charge has a terminal voltage of 12 volts with a internal resistance of .010 ohms, then a 10 amp charge current is only going to raise the battery voltage 10 amps x .010 ohms = .1 volts or 12.1 volts. The controller will continue to supply 10 amps to the battery until it reaches the Bulk Set Point of 14.1 volts which will be many hours until it reaches 14.1 volts or whatever the set point is.

            To take that battery from 12 volts to 14.1 volts would take a current source of roughly [14.1 - 12 volts] / .010 Ohms = 210 amps or about a 4000 watt solar panel with a PWM controller. Of course if you did that o such a small battery it would explode.
            MSEE, PE

            Comment


            • #7
              Originally posted by Sunking View Post

              To take that battery from 12 volts to 14.1 volts would take a current source of roughly [14.1 - 12 volts] / .010 Ohms = 210 amps or about a 4000 watt solar panel with a PWM controller. Of course if you did that o such a small battery it would explode.
              This is where the C/8 for a FLA comes into play right?

              Comment


              • #8
                Originally posted by mschulz View Post
                This is where the C/8 for a FLA comes into play right?
                Yes, but FLA would be expected to gas too vigorously, losing a lot of electrolyte out the vents, possibly overheat and possibly suffer plate erosion. Not likely to blow up or lose electrolyte which cannot be replaced like for the sealed kinds.
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

                Comment


                • #9
                  Originally posted by Sunking View Post
                  What you do not understand is Bulk, Absorb, and float are only set points in which the controller switches from one state to another. Bulk is setting to run the controller in a Constant Current Mode, and the panels can only produce X amount of current. Iv the case of a PWM controller Input Current = Output Current. So if you have 170 watt 12 volt battery panels all you are going to get is 10 amps at best.

                  Now if your 12 volt battery is at 50% State of charge has a terminal voltage of 12 volts with a internal resistance of .010 ohms, then a 10 amp charge current is only going to raise the battery voltage 10 amps x .010 ohms = .1 volts or 12.1 volts. The controller will continue to supply 10 amps to the battery until it reaches the Bulk Set Point of 14.1 volts which will be many hours until it reaches 14.1 volts or whatever the set point is.

                  To take that battery from 12 volts to 14.1 volts would take a current source of roughly [14.1 - 12 volts] / .010 Ohms = 210 amps or about a 4000 watt solar panel with a PWM controller. Of course if you did that o such a small battery it would explode.
                  I get it now, Thanks Sunking.

                  Comment


                  • #10
                    Originally posted by mschulz View Post
                    This is where the C/8 for a FLA comes into play right?
                    Well yes and no. My example was a theoretical battery with an internal resistance of .01 Ohms and the function of Current passing through a Resistance developing a Voltage. All part of Ohm's Law.

                    C/H can be either a Discharge or Charge specification. Where C = the battery Amp Hour Capacity usually at the 20 hour discharge rate, and H = time in Hours. It called the C rate for Charge and Discharge. So if you have a 100 AH battery the C/8 rate is 100 AH / 8 Hours = 12.5 Amps. It is really simple math = Amps = Amp Hours / Hours.

                    What is important to take away is batteries limits to how much current they can be charged and discharged with. This is where the battery internal resistance becomes a significant factor. The higher the resistance, the less current the battery can charge or discharge. So as a general rule a Deep Cycle FLA you want to limit to about C/8 maximum. There are exceptions like a hybrid battery, and of course a SLI battery can withstand very high charge and discharge currents.

                    AGM batteries have lower internal resistance than FLA. AGM you want to limit to a maximum of about C/4. Like FLA there are exceptions like AGM's made for UPS system that can take as much as 1C.

                    One thing you have to look out for and we see this a lot here is folks take something like a 12 volt 100 AH battery and connect it to 2000 watt inverter. At 2000 watts at 12 volts requires in excess 170 amps. So if we take the example I used which is realistic of having a internal resistance of .01 Ohm's and try to draw 170 amps the battery voltage will sag from 12.6 volts down to 10.9 volts. It is not going to work.
                    MSEE, PE

                    Comment


                    • #11
                      Originally posted by Sunking View Post
                      200 watts = 200 watts on paper.

                      However if you use a MPPT controller the charge current @ 12 volts = 200 watts / 12 volts = 16.6 amps. You would wire the panels in series even on a 12 volt battery. For 24 volt the the charge current would be 200 watts / 24 volts = 8.3 amps.

                      Now with that said if you were to use a PWM controller is the example you really gave. If you were to use a PWM controller you are forced to wire the panels in parallel for the 12 volt battery and current would be 10 amps or roughly 120 watts with 200 watts input. With PWM controller Current In = Current Out. With MPPT Current Out = Power In / Battery Voltage. Huge difference.

                      Thanks a lot!

                      Comment


                      • #12
                        with 200watts on paper, I would expect 160W in real life, any more is bonus from cool air, breeze, or extra clear sky.
                        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                        solar: http://tinyurl.com/LMR-Solar
                        gen: http://tinyurl.com/LMR-Lister

                        Comment

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