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Gonna try to install a few garden lights.

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  • Gonna try to install a few garden lights.

    I plan to install a few 12v led lights on a short rock wall next to some rock steps, hidden and to shine down on the steps. With a dusk to dawn switch or a timer. I found some auto license plate lights, 12v (9-14.8), .5W, 35 mA draw. I want to install 2, maybe 3 of these. The landscape wires would be about 10 feet long, 16 awg. I bought a cheap charge controller that has a dusk/dawn switch on it, I think it is 7A. The only instructions I have is what wires go where. It has a charge light and load light. I think it cuts the load off at 11somethingV and the charge at 14somethingV. I hooked it all up with a new 12V, 5A battery. It worked for about 6 hours and went off (I also had a strip LED hooked up at the same time)1W, 130mA). I'm not sure if the CC has a timer or the voltage drained bellow the load cut off. I tested the battery with an analogue tester, it needs charged, was about 12.0 V but not sure how accurate the tester is.. I still have to get a solar panel and see if it all will work together.

    if the lights are .5W each, is that .5W per hour? as in 2 lights X .5WH X hours on per day (night). if on 12 hours per day (night) it would be 12wh/d ? and if that is right, then it would draw 1 amp per day? 12WH/12V=1A? And if that is correct, that would be 20% of my 5A battery plus what the CC and wire draws? And if all that is correct, what size PV should I have? not much sun here in SW ohio and sort of in the woods, maybe get 3-4 hrs of direct sun on a PV on a good day. Also, should I have fuses anywhere?

  • #2
    Originally posted by R1campr View Post
    I
    if the lights are .5W each, is that .5W per hour? as in 2 lights X .5WH X hours on per day (night). if on 12 hours per day (night) it would be 12wh/d ? and if that is right, then it would draw 1 amp per day? 12WH/12V=1A? And if that is correct, that would be 20% of my 5A battery plus what the CC and wire draws? And if all that is correct, what size PV should I have? not much sun here in SW ohio and sort of in the woods, maybe get 3-4 hrs of direct sun on a PV on a good day. Also, should I have fuses anywhere?
    Let's get this started on the right foot:

    Watts are a measure of power, that is energy delivered per unit of time. Watts per hour (watts divided by hours) is meaningless.
    Watt-hours (watts times hours) is a measure of total energy, like the energy which a battery can store.

    Your .5watt lights each use .5watt-hours every hour that they are turned on. If you run them for 8 hours, that is 4watt-hours each per day.

    On the other side, if you have a 12 volt 10Amp-hour battery, that battery will hold 120watt-hours of energy. [B]But[/B] for decent battery life you should not try to use more than about 20% of that before recharging. So that hypothetical battery could reasonably give you 24 watt-hours. That would be 6 of your LED lights for 8 hours.

    The controller you got may have a settable length of time that the lights stay on after dark. (Dark is determined by looking at the solar panel input to the CC, so without a panel, it will not work properly.) Or it may leave the lights on during darkness until the battery voltage drops so low that it turns them off to protect that battery. That is probably well beyond the 20% goal.

    If you do not have the solar panel yet, you need to use something else to recharge your battery. Sitting partially discharged is not good for it.
    My guess is that you have a sealed battery, either AGM or GEL. For solar PV, GEL is not the best choice.

    If you are going to run two lights for 12 hours each night, then you need to make up 12 watts of energy each day. Because of inefficiencies in the CC, you wiil want a panel rated to deliver twice that energy. And if you only get direct sunlight on the panels 3-4 hours per day (hopefully near noon!) you can only count on the equivalent of one or two hours per day, especially in winter. That would require at least a 20 watt panel, but larger would be better.
    This panel would deliver about 1 amp to recharge the battery, which is a reasonable current for a 5-10 AH battery. With your 7 amp CC, you do not want a very large panel since it might try to charge the battery too fast. Look at the battery specifications to see what the maximum charging current is.
    For a 5AH AGM battery, it may be 5 amps or more. For a GEL battery, it may be less than 1/4 amp.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Thanks inetdog for replying, I appreciate your help. Checking the battery I have, it says its lead calcium, I couldnt find a max current charge rate on it.

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      • #4
        Originally posted by R1campr View Post
        Thanks inetdog for replying, I appreciate your help. Checking the battery I have, it says its lead calcium, I couldnt find a max current charge rate on it.
        OK. We still need to know whether it is AGM or GEL (or even FLA). Is it a sealed battery? If you give us the manufacturer and model, and/or a photo of it, we might be able to find out more about it.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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