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  • AH of this NAPA battery?

    I have a napa battery (no. 8301). While it gives some stats, such as rc as 175 and cranking amps, it doesn't provide the ah. Is there any way to figure that out? Napa does call it an rv deep cycle battery. Catalog description is here:

    http://www.napaonline.com/Catalog/Ca...301_0213555773

    Tim

  • #2
    They do not list Amp Hours because it is not a deep cycle battery. When you see a battery with CCA and RC ratings tells you right away it is a Starting Battery or Hybrid when RC rating is specified. Now with that said you can get a pretty good idea what the AH rating is from the RC spec. RC (reserve capacity) is the amount of time in minutes a battery can deliver 25 amps. So the battery RC = 175 minutes. Convert minutes to hours and multiply by 25 amps. So 175 = roughly 3 hours x 25 amps = 75 AH Thing is that is its 3 hour rating. Batteries are usually specified @ 20 hours so that puts the battery up around 100 to 115 AH
    MSEE, PE

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    • #3
      Thanks

      Thanks sunking.

      Not a true deep cycle...I'm 66 years old and still believe what a salesman tells me...have to share some of the blame myself...As in..."geez, that's a good price, I should pick these up."

      Tim

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      • #4
        Tim it will work, just may not last as long as you would like.
        MSEE, PE

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        • #5
          Originally posted by TimDex View Post
          Thanks sunking.

          Not a true deep cycle...I'm 66 years old and still believe what a salesman tells me...have to share some of the blame myself...As in..."geez, that's a good price, I should pick these up."

          Tim
          The 36 month warranty is an indicator that it might not be an RE battery type.
          Also, an RE battery may be capable of long deep discharges, but that is not the way they will typically be used, so the way that occupies a dominant place in the advertising is also an indicator.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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          • #6
            Another way to do it is to just multiply the RC by 0.6

            175 * 0.6 = 105ah (roughly)

            Good enough for quick determinations. Don't fret the Napa battery, although not a true RE type, it makes a good learner's battery before investing in true RE. If you are going to make a mistake, these are the types to learn on.

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            • #7
              Originally posted by PNjunction View Post
              Good enough for quick determinations. Don't fret the Napa battery, although not a true RE type, it makes a good learner's battery before investing in true RE. If you are going to make a mistake, these are the types to learn on.
              Ditto, I agree. NAPA is made by Interstate. Interstate makes a whole lot of batteries with different store names like Wally World, Agent Orange, Blue Box, ect...
              MSEE, PE

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              • #8
                Thanks

                Thanks for the good information and advice.

                An additional question I have is choosing the correct sized controller for a battery. If you want to hit the sweet spot of a c/10 rate, where the current is equal to the amp hours divided by 10, how do you actually determine the current?

                Do you take the wattage of the panel and divide by battery voltage, or do you take the amps as provided by the panel specs?

                For example, in a small system with a 140 watt 12 volt panel, with specs that say it hits about 7.9 amps, is the current flowing through the controller to the battery that 7.9 amps, or is it 140/12, or about 11 amps?

                Pardon my probably dumb question but I'm getting hung up on this.

                Tim

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                • #9
                  Originally posted by TimDex View Post
                  Thanks for the good information and advice.

                  An additional question I have is choosing the correct sized controller for a battery. If you want to hit the sweet spot of a c/10 rate, where the current is equal to the amp hours divided by 10, how do you actually determine the current?

                  Do you take the wattage of the panel and divide by battery voltage, or do you take the amps as provided by the panel specs?

                  For example, in a small system with a 140 watt 12 volt panel, with specs that say it hits about 7.9 amps, is the current flowing through the controller to the battery that 7.9 amps, or is it 140/12, or about 11 amps?

                  Pardon my probably dumb question but I'm getting hung up on this.

                  Tim
                  That will depend on the voltage of the battery and type of controller.
                  With MPPT amps to the battery is W/battery voltage.
                  With PWM amps in = amps out. You will lose approx 30% of the power of the panel with this type of controller

                  So say you use a 140W 12V panel
                  Vmp of that panel is about 18V and amps about 7.7 amps into your battery with a PWM controller
                  Same panel with MPPT controller 140/12=11.66 int the battery.
                  If you say buy a grid tie 60 cell panel which will be about 1/2 the cost of the 140W 12V panel the pwm losses get worse.
                  NABCEP certified Technical Sales Professional

                  [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

                  [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

                  [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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                  • #10
                    Originally posted by TimDex View Post
                    For example, in a small system with a 140 watt 12 volt panel, with specs that say it hits about 7.9 amps, is the current flowing through the controller to the battery that 7.9 amps, or is it 140/12, or about 11 amps.
                    Close - you just divide the panels rated wattage, by it's ocv rating, typically in a 12v-nominal system that will be anywhere from 17-21v. For quick calculations, just use 18v.

                    140 watts / 18 volts = 7.77 amps. Pretty close to what they spec.

                    But you always buy a bit more amperage capability than the panel, so if it were me, I'd choose either a 10A controller, or maybe 15A unit.

                    This doesn't take into account real-world losses as mentioned above, like from PWM controllers. However this best-case scenario has some built-in headroom to keep the system from being on the edge spec-wise.

                    Pwm or mppt controller choice is up to you. Note that for small systems under 200 watts, it may make more sense financially to just buy more panel power, than to spring for a costly mppt controller. Various threads exist here to debate the pros and cons.

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                    • #11
                      Originally posted by TimDex View Post
                      TFor example, in a small system with a 140 watt 12 volt panel, with specs that say it hits about 7.9 amps, is the current flowing through the controller to the battery that 7.9 amps, or is it 140/12, or about 11 amps?
                      Depends on controller type.

                      If PWM then Input Current = Output Current, So 7.9 amps.
                      If MPPT then Panel Wattage / Battery voltage = Current Output. 140 watts / 12 volts = 11 amps
                      MSEE, PE

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                      • #12
                        Originally posted by Naptown View Post
                        That will depend on the voltage of the battery and type of controller.
                        With MPPT amps to the battery is W/battery voltage.
                        With PWM amps in = amps out. You will lose approx 30% of the power of the panel with this type of controller

                        So say you use a 140W 12V panel
                        Vmp of that panel is about 18V and amps about 7.7 amps into your battery with a PWM controller
                        Same panel with MPPT controller 140/12=11.66 int the battery.
                        If you say buy a grid tie 60 cell panel which will be about 1/2 the cost of the 140W 12V panel the pwm losses get worse.
                        Originally posted by PNjunction View Post
                        Close - you just divide the panels rated wattage, by it's ocv rating, typically in a 12v-nominal system that will be anywhere from 17-21v. For quick calculations, just use 18v.

                        140 watts / 18 volts = 7.77 amps. Pretty close to what they spec.

                        But you always buy a bit more amperage capability than the panel, so if it were me, I'd choose either a 10A controller, or maybe 15A unit.

                        This doesn't take into account real-world losses as mentioned above, like from PWM controllers. However this best-case scenario has some built-in headroom to keep the system from being on the edge spec-wise.

                        Pwm or mppt controller choice is up to you. Note that for small systems under 200 watts, it may make more sense financially to just buy more panel power, than to spring for a costly mppt controller. Various threads exist here to debate the pros and cons.
                        Originally posted by Sunking View Post
                        Depends on controller type.

                        If PWM then Input Current = Output Current, So 7.9 amps.
                        If MPPT then Panel Wattage / Battery voltage = Current Output. 140 watts / 12 volts = 11 amps
                        ^^^Priceless...
                        and this is why solarpaneltalk.com is #1.
                        [CENTER]SunLight @ Night[/CENTER]

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                        • #13
                          Originally posted by Sunking View Post
                          If PWM then Input Current = Output Current, So 7.9 amps.
                          If MPPT then Panel Wattage / Battery voltage = Current Output. 140 watts / 12 volts = 11 amps
                          Exactly! This shows that even though there is only a 3 amp difference, at this small scale, it might be cheaper and just as effective to get just a bit more panel with a standard pwm controller.

                          However, when you start ramping up in power, especially over 200 watts, or if you have low solar-insolation hours like in the pacific northwest, this will make a BIG difference, and MPPT would be the better choice even at a small scale. But as mentioned elsewhere, if you go MPPT you must get serious, otherwise cheapskate mppt's with poor voltage tracking may net you no real improvement over a standard pwm, and only lighten your solar wallet.

                          Choices ....

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