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Solar Garden LED lights upgrade.

Discussion in 'LEDs and Optoelectronics' started by Rowan, May 14, 2015.

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  1. Rowan


    May 14, 2015

    I wonder if someone can give me practical advice.

    Over the last few years I have made a number of purchases for garden "chain" LED lights which are solar powered. The lights switch on automatically at dusk and switch off at dawn. But the product rarely lasts more than a year as the battery efficiency deteriorates fairly quickly. As mentioned the weak point of the system is the batteries, these eventually only stores enough current for an hour to two after a few months. That said, I have managed to change the batteries on a number of occasions and I am now looking to make a permanent upgrade for the whole system

    The actual LED' lights, cables and connection are robust and never seam to fail.

    I am not technically minded nor have the knowledge to calculate efficiencies; but I am practical, and have a better than average acumen when it comes to tinkering with electronic components. I therefore propose to change the standard solar panel and battery to power the current LED string lights and add another set of LED lights.


    1) use a larger battery to store more electricity to allow the lights to stay on over night. The battery would also hopefully retain excess charge should we have any cloudy days.
    2) run further LED lights. These will be used to illuminate some small trees and a covered area.

    Proposed purchases for the project

    The following solar cell.

    The following solar charge regulator.

    Standard car battery

    The following step down transformer to power LED’s

    The following lights
    plus two of these light units (6 lamps in total)

    Questions I would like answered.

    a) is the car battery the most efficient battery for this purpose. Should I be looking for a 5v long lasting car battery instead. If so, any suggestions?
    b) will this solar cell be good enough to fully charge a car battery on a sunny day - say minimum 7 hours of sun?
    c) is the following solar regulator appropriate to use with solar cell / battery / step down transformer / and all the above LED lights?
    d) is the step down transformer an efficient way of using the stored current?
    e) in your opinion would the set up be sufficient to power the lights for 8 hours during the night for say 4 days without charging?
    f) any suggestions for ready made dust to dawn sensors?
    g) would you do anything else differently for this project?
  2. donkey


    Feb 26, 2011
    a) well a car battery is 12volts..... LED's use less than that worry more about the amp hour rating for length of time. also car batteries need to have charge over 50%at all times or they tend to suffer
    b) the solar panel is 10w, on a full sun day you will get (watts divide volts=current) less than 1 amp. the car battery is 35ah... you need at least 35hours of light to fully charge.
    c)the charge regulator shows the maximum amps through the controller. both for load and for charging. so will it handle the charging? yes. will it handle the load? maybe...
    d) will leave for others to decide but will go with no... transformers are AC, so it has to be rectified... loss of power.
    e) the lights to battery ratio is simple. how many amp hours in battery divide load, so 35/ 6 amps = bout 6 hours(example, LEDS will use less then 6amps)
    f) ebay might be easy, type in dark sensor or PE cell
    g)personally I would downsize the volts, increase the amps for about the same price. also the lights you linked to have inbuilt batteries now... kinda defeats the purpose of having batteries.
    secondly I would try to get everything at the same voltage, saves having to have step down transformers which can have a loss.
    also more parts means more things can go wrong. simplicity is key.
    the controller you linked doesn't have over charge protection
    car battery is rated at 12volts need to downsize etc, a 6volt battery same physical size will create more amp hours so if you have a few days with limited light it will last
  3. Gryd3


    Jun 25, 2014
    I agree with everything in here but would like to mention to the OP that a transformer can't be used with a battery, as the battery operates on Direct Current. A transformer relies on Alternating Current to operate. So if you 'really' wanted a transformer, you would need an inverter to feed the transformer and a rectifier afterward to convert back to DC for the lights.
    An alternative solution is a 'Buck Converter' . This works with DC and has similar properties to a transformer. Output Voltage goes down, Output Current goes up.

    I think you need to re-approach your angle of attack here Rowan.
    Step 1) Determine Maximum amount of lights and their power draw. (If you can make everything the same voltage this will help a great deal.)
    Step 2) Determine the Maximum run time you would like for the lights.
    Step 3) Using Step 2, you can figure out a battery size for your project.
    Step 4) figure out on average how much sun you get daily to determine the solar panel(s) you need to fully charge the batter every day.

    The important part here is that you need to collect as much energy during the day that you plan to spend at night. You could have 1 Million Amp Hour battery, and if your setup uses 60Ah every night you will need to collect at least 60Ah during daylight or you battery will simply spend most of it's time dead regardless of size.
  4. Externet


    Aug 24, 2009
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