My first post and help with a project

Discussion in 'Circuit Help' started by Chris Cook, Jul 16, 2017.

  1. Chris Cook

    Chris Cook

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    Hello all!

    I have been putting these low cost, LED light strings on random trees on the back of our property. This gives a neat highlight to the view out of our back windows.

    So far I have about 8 separate strings on 8 trees (I plan to do many more). Each are individually solar-charged & powered with a 1.2V nickel–metal hydride battery using a 5"x5" solar panel (see reference photos below).

    Since all the panels get varying amounts of sunlight and the batteries will all reach end-of-life at different times, I would like to centralize the power by getting a larger solar panel and battery to supply all the units. This way I could place the solar panel/charge station in a good spot and use this for all the light strings.

    Home depot has a small solar kit for a 12V battery charge setup (see link below). This is one thing I looked at for this. I am looking for ideas on how best to do this.

    http://www.homedepot.com/p/Grape-Solar-50-Watt-Off-Grid-Solar-Panel-Kit-GS-50-KIT/206877151

    I appreciate your help and forgive my ignorance int his regard.

    CC



    [​IMG]
     

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    Chris Cook, Jul 16, 2017
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  2. Chris Cook

    Harald Kapp Moderator Moderator

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    Cool avatar you have there :cool:

    Regarding your setup:
    You will need an additional 12 V battery, but of course you are aware of this.
    You will then need voltage regulators to step down from the battery's 12 V to teh LED strings' 3.6 V. To minimize power loss (optimize battery usage) use a switch mode step down regulator. Here is an example.
    As you will be running rather long wires from the central battery to the LED strings, I recommend you route the 12 V from the battery to the trees, then place one step-down converter (12 V down to 3.6 V) next to each tree. Chose the step-down regulator such that the nominal output current is at least 10 % more than the current required by the LEDs. his will improve the lifetime of the converters. Use one converter per tree. This will cost a bit. The advantage is that the current on the 12 V wire is much lower than it were the case with a single central step down regulator. You can therefore use thinner wire and more of the battery power is available for the LEDs (instead of heating the wires).
    Here's how I imagine your setup:
    upload_2017-7-17_18-26-29.png

    A step down converter is a sensitive piece of electronic. Put it in a well sealed plastic case to prevent any moisture from entering. If you don't seal it well, it will not take long for moisture to start corroding the regulator.
     
    Harald Kapp, Jul 17, 2017
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  3. Chris Cook

    Audioguru

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    One original battery is 1.2V at 1800mAh so if it lasts for 6 hours then its current is 1800/6= 300mA. Its power is 1.2V x 300mA= 0.36W and eight of them total 0.36W x 8= 2.88W. Why did you select a solar panel that is 50W (17 times too big and too expensive)? A solar panel for trickle-charging a car battery costs $10.00 when on sale and produces about 2.5W.

    A red LED is 3.6V/2 as shown by Harald but aren't your LEDs 3V to 3.2V white ones? Then connect three of your LEDs (remove them from the solar circuit) in series and in series with a 330 ohms resistor and connect this string to the new 12V battery.

    Since you will not be using the original 1.2V solar circuit then the LEDs will be turned on all day, then the battery will not charge unless you manually turn them off.
     
    Audioguru, Jul 18, 2017
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  4. Chris Cook

    Chris Cook

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    Thanks for your responses. I simply chose the home depot kit as an example (and out of ignorance) I am looking for a day-charging solution that will power the lights at night.

    This is the flipside of the board (attached).

    I would be happy to build a system that is basically a large version of the one first pictured: Solar panel, battery, LED controller and light sensor.
     

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    Chris Cook, Jul 18, 2017
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  5. Chris Cook

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    The original circuit is completely different to what you want:
    It uses a 2V solar panel and a 1.2V battery cell. When there is no voltage from the solar panel (in the dark) it switches off the charging and switches on the LED. When there is voltage from the solar panel then it switches off the LED and switches on the charging. The circuit boosts the 0.8V to 1.4V from the battery cell to a current-limited 3.4V to feed all the LEDs in parallel.

    Your new system will have a 14V solar panel and 12V battery. You must design or find a circuit to switch the charging and the LEDs since the voltage is much too high for the original circuits. A voltage booster is not needed and you can remove the LEDs from the original circuits and connect 3 LEDs in series and in series with a current-limiting resistor. A lot of work!

    Maybe you can use the 14V charger and 12V solar panel with a 1.2V LM317 voltage regulator. It throws away most of the battery power heating the voltage regulator. It can power about 4 solar systems. Or you can buy a 12V to 1.2V buck voltage reducing circuit from ebay that can produce 1.2V at 2.4A so it can power 8 of the solar systems.
     
    Audioguru, Jul 18, 2017
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  6. Chris Cook

    Chris Cook

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    Chris Cook, Jul 20, 2017
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  7. Chris Cook

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    The original 2V solar panel controls the LED turning on or turning off. With your new circuit then it will not happen unless you fiddle with a voltage divider from the 14V solar panel.

    I do not knows what the output of the buck converter will do when the original circuit tries to "charge" it.
     
    Audioguru, Jul 20, 2017
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  8. Chris Cook

    Chris Cook

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    IMG_0591.jpg
    So I have gotten the charger to work with the battery and the battery working through the buck converter to power the lights.

    What I need to do is have a photo cell action where sunlight will trigger A to be CLOSED and B to be OPEN. (And the opposite actions in darkness)

    Any help is much appreciated.

    CC
     
    Chris Cook, Jul 30, 2017
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  9. Chris Cook

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    "A" is usually a diode. A Schottky diode has less voltage drop than a silicon diode. The diode passes charging current when the solar panel is in sunshine and blocks the solar panel from discharging the battery when in darkness.

    "B" in most solar garden lights is part of the IC that controls everything and it senses when the solar panel is in sunshine or not. old solar garden lights used a Light Dependent Resistor (LDR).
     
    Audioguru, Jul 31, 2017
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  10. Chris Cook

    Chris Cook

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    Audioguru,

    you are da man!!

    Thank you!
     
    Chris Cook, Jul 31, 2017
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