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  • Monocrystalline solar cells for portable stereo

    Hi there. I am building a stereo that utilizes a low power amplifier (400mah under use) along with a 12v 18ah SLA battery. I plan on using (4) 5W Monocrystalline solar panels (http://www.aliexpress.com/snapshot/217472836.html that is what I have already purchased).

    I am thinking I can only actually use 3, since I need charging to be around 14-16v (equivalent to three panels) and my fourth is going to be useless. Is that true?

    Thanks so much for the advice.

  • #2
    Originally posted by wy2quiet View Post
    Hi there. I am building a stereo that utilizes a low power amplifier (400mah under use) along with a 12v 18ah SLA battery. I plan on using (4) 5W Monocrystalline solar panels (http://www.aliexpress.com/snapshot/217472836.html that is what I have already purchased).

    I am thinking I can only actually use 3, since I need charging to be around 14-16v (equivalent to three panels) and my fourth is going to be useless. Is that true?

    Thanks so much for the advice.
    You will need a charge controller (CC) to prevent the cells from overcharging the battery. If you get a PWM CC then you will need a total Vmp of 18 volts or more. That would be at least three panels and possibly even the full set of 4. Adding the fourth panel will not necessarily get you more power if you use a PWM controller, but it will not hurt anything either, and it will allow the CC to operate more reliably.
    If you find an inexpensive MPPT controller, you would be able to use the full power of the first three and also the added power from the fourth panel. You would get a charging current which is greater than the panel Imp of about 1 amp.
    20 watts or more of panel will be fine with that size SLA battery. (Is it AGM (good) or GEL (bad)?)

    With a load of .4 amps (not amp-hours!), the battery could safely power the stereo for as long as 18 hours before being recharged.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Originally posted by inetdog View Post
      You will need a charge controller (CC) to prevent the cells from overcharging the battery. If you get a PWM CC then you will need a total Vmp of 18 volts or more. That would be at least three panels and possibly even the full set of 4. Adding the fourth panel will not necessarily get you more power if you use a PWM controller, but it will not hurt anything either, and it will allow the CC to operate more reliably.
      If you find an inexpensive MPPT controller, you would be able to use the full power of the first three and also the added power from the fourth panel. You would get a charging current which is greater than the panel Imp of about 1 amp.
      20 watts or more of panel will be fine with that size SLA battery. (Is it AGM (good) or GEL (bad)?)

      With a load of .4 amps (not amp-hours!), the battery could safely power the stereo for as long as 18 hours before being recharged.
      http://www.saskbattery.com/linked/ub12180.pdf

      It is AGM. With the amplifier I am using, there have been about 10-20 of these boxes built that can go for 50+ hours with the equivalent sunlight that averages in the Danish summers (where most of these boxes were built). Most of them use 10W however, and I wanted to double it.

      I don't want to spend alot on a charge controller since to be honest the entire setup is like $300. I saw an ebay MPPT (chinese, lol) for around $35 shipped. Are they legit in the sense that they do what they are supposed to?

      Thanks again for responding.

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      • #4
        Originally posted by wy2quiet View Post
        I don't want to spend alot on a charge controller since to be honest the entire setup is like $300. I saw an ebay MPPT (chinese, lol) for around $35 shipped. Are they legit in the sense that they do what they are supposed to?
        Some have been known to just be pwm or even simpler on/off types with mppt silkscreened on the case. I would start with a quality Morningstar Sunguard 4.5a rated fully-encapsulated, temperature compensated, pwm controller for the same price. The difference is that you'll pay for the Morningstar once. With the others, buy two - or four just in case.

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        • #5
          Originally posted by wy2quiet View Post
          http://www.saskbattery.com/linked/ub12180.pdf

          It is AGM. With the amplifier I am using, there have been about 10-20 of these boxes built that can go for 50+ hours with the equivalent sunlight that averages in the Danish summers (where most of these boxes were built). Most of them use 10W however, and I wanted to double it.

          I don't want to spend alot on a charge controller since to be honest the entire setup is like $300. I saw an ebay MPPT (chinese, lol) for around $35 shipped. Are they legit in the sense that they do what they are supposed to?

          Thanks again for responding.
          If you decide on a cheapo charge controller make sure it is compatible with your AGM battery. Some are set for FLA only charging programs.

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          • #6
            After spending a couple hours looking at my options, I think I am going to get the Genasun 5A MPPT charger.

            It seems there technology has some serious advantages, and is also as efficient, or MORE, than the expensive $300+ units (98-99.7%). It also uses millisecond MPPT sweeping, so that sounds good. Considering the price at $70, I don't think I can really go wrong since it will be a good investment.

            Also since the panels I purchased are not THAT expensive, I am also considering using some foldable mirrors to help concentrate the sunlight (small ones, not large enough to heat/damage the panels). I figure it should give me near the percentage to help compensate for the fact I am at a moderate latitude (Ottawa, Ontario).

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