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Problem with 2 solar panel hookup.

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  • #16
    I think you are just making assumptions are not TRUE leading you to the wrong conclusions. Let's start with the first oversight of comparing input current and voltages with output voltage and current. With a MPPT Controller Output Current = Panel Wattage / Battery Voltage.

    It is an important to understand the formula, because if you did you would know Output Current is always higher than Input Current period end of story. A MPPT Controller is a POWER CONVERTER, not a series or shunt voltage regulator like PWM.

    So take one of your panels, assuming the battery is discharged, and you input say 17.6 volts @ 5.68 amps = 100 watts input to the controller. MPPT is a Power Converter and the power is 100 WATTS. On the output you measure the voltage and current and see 12.4 volts @ 8.1 amps = 100 watts, same as input power. Voltage and Current will NOT BE EQUAL between Input and Output. Power will be equal. We have converted 100 watts being input at 17.6 volts @ 5.68 amps and converted to 100 watts into 12.4 volts @ 8.1 amps. Power is Equal between In and Out.

    The other issue you are likely not considering is your battery is nearly fully charged. So with just one panel the battery charge is just low enough to accept full charge POWER, but when second panel is added the charger is in the CV mode and the batteries cannot take full power when nearly charged up. It wil be more than one panel, but not full power of both panels.

    If you want to see what the controller and panels can do is apply a heavy load that drags the voltage down to 12 volts. So if you have 200 watts of panels, try a 400 watt load.
    Last edited by Sunking; 07-09-2018, 07:16 PM.
    MSEE, PE

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    • #17
      So, Ill bring the trailer home and hook it up to see where it gets me.

      It sounds to me like the problem with my testing is having it hooked up to a full battery.

      will report back when I have tested under load, see if it changes

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      • #18
        You just need to Load Test the system. Once the batteries are charged up, the system does nothing if there is no load to discharge the batteries or someplace for power to go. Just like filling up your cars gas tank and parking your car indefinitely. No place for the gas to go and be used.
        Last edited by Sunking; 07-12-2018, 04:04 PM.
        MSEE, PE

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        • #19
          Well looks like that may have been the issue.

          I hooked up the batteries to the trailer and reconnected the whole system. I turned on all lights, fans, radio etc.

          The amps did indeed jump up to around 8-9 from the controller to the battery. At 12.7 volts.

          Guess they are working ok after all. Thanks for the tips guys I was ready to call it quits with these panels.


          On a side note. What is anyone opinion on a better setup for the roof of the trailer. Both are about the same distance as far as wiring setup goes.







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          • #20
            [QUOTE=CanadianEhh;n380489]

            On a side note. What is anyone opinion on a better setup for the roof of the trailer. Both are about the same distance as far as wiring setup goes.




            You really need to keep your panels away from the AC unit, crank up vents and any other potential shadow makers. While in this photo it appears ok at different times of the day, and while parked at different angles to the sun you will get shadows. If you have a shadow, even a small one it will pretty much take said panel, or string, if series wired, out of the charging loop.
            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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            • #21
              Well one of the worst offenders for potential shadows on the roof is the TV antenna. But there isnt alot of other real estate available away form it or the AC unit. The roof is curved, so I wasnt sure I wanted to be to one side or the other, but rather directly in the middle at the crest of the curve? I was worried putting them across the curve like the lower picture would create too much curvature on the flexible panel to be effective at gathering the most possible sun. The top picture they pretty well lay flat rather than curved at all, but are much closer to a shad producing tv antenna.

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              • #22
                TV antenna?? what is that? Thought everybody had dishes or domes these days.
                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                • #23
                  Originally posted by CanadianEhh View Post
                  Well one of the worst offenders for potential shadows on the roof is the TV antenna. But there isnt alot of other real estate available away form it or the AC unit. The roof is curved, so I wasnt sure I wanted to be to one side or the other, but rather directly in the middle at the crest of the curve? I was worried putting them across the curve like the lower picture would create too much curvature on the flexible panel to be effective at gathering the most possible sun. The top picture they pretty well lay flat rather than curved at all, but are much closer to a shad producing tv antenna.
                  A relatively small curvature probably won't have much of an effect on output, but (and not that it matters a whole lot in the bigger set of considerations) what reduction in net input of irradiance there may be from roof curvature will perhaps come as much from increased glazing reflectance as f(incidence angle) as from reduced POA irradiance as f(incidence angle). Overall, probably not worth worrying about. Shadows will be the big concern.

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                  • #24
                    Originally posted by littleharbor View Post
                    TV antenna?? what is that? Thought everybody had dishes or domes these days.
                    Well the trailer is from 2008. so yes it still have an antenna. Which we do use as depending on where we are camping, we can get 5-10 fully digital HD channels over the air for free.

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                    • #25
                      As long as your viewing hours are late afternoon thru early morning you could just crank it up and down as needed.
                      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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