Solar light question




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  1. #1
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    Default Solar light question

    Okay I am a bit confused. I made a garden light using a 9watt 12v led bulb, a 10Amp solar requlator and a 30watt solar panel. So at least there is some light outside when we have a power failure.

    Now I use 2 x 12v 7.2Ah batteries in parallel connected to the solar regulator. Now I used a few online calculators and even with one battery it should shine for 8 hours or so. I reckoned that 2 batteries would be more than enough to run it till the sun comes up. But after 2 hours or so the regulator shuts off the load. I had two old batteries that was still good, and then I went an bought two brand new one's, same result.

    Was my calcs wrong? Is the regulator faulty? Any suggestions? I will remove the bulb and do some testing without the regulator...
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  2. #2
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    Default Re: Solar light question

    Silly question but have you checked the battery voltage?
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  3. #3
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    Default Re: Solar light question

    And what make/model is the solar controller? It may have a high voltage cut/off setting.

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  4. #4
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    Default Re: Solar light question

    Quote Originally Posted by jelo View Post
    Silly question but have you checked the battery voltage?
    I will confirm with multi meter tonight what the voltage is when the light goes off just in case, I charged the new one's beforehand, showed 13v when I installed them, was dark already and light went on, but as mentioned, after about 2 hours or a bit more, went off.

    When the older batteries was in, regulator indicated at about 13:00, that the batteries was fully charged, run time still about 2-3 hours.
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  5. #5
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    Default Re: Solar light question

    Quote Originally Posted by Subok View Post
    And what make/model is the solar controller? It may have a high voltage cut/off setting.
    It's a chinese special

    Small R200 jobbies. But you agree that two 7.2 ah batteries is more than enough to run 9w 12v light?

    I suspect the regulator could be the problem, I just wanted to make sure I didn't miss anything when sizing the battery for the application.
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    Default Re: Solar light question

    The led should use between 800ma to about an amp, so should be correct. I would suggest checking the actual amount of current that it is drawing to get an actual figure to calculate from. Charge the batteries with a charger and then measure from there. Make sure the solar panel is in fact charging the batteries, you will need to measure the voltage and amperage output.

    How does it switch on, does it have a day/night sensor. If it is on all the time it is possible that the led is taking more power than what is going in from the solar panel. Does the solar panel have the correct wire size. Does the controller have an adjustment for low voltage cutout. Also measure the voltage when it does cut out, it could be at the wrong cut out voltage.

  7. #7
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    Default Re: Solar light question

    7W @ 12VDC = 0.6A

    two x 7.2Ah batteries in parallel should give 14 ah

    14ah / 0.6A = 23 hours
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    Default Re: Solar light question

    Quote Originally Posted by staalwol View Post
    Okay I am a bit confused. I made a garden light using a 9watt 12v led bulb, a 10Amp solar requlator and a 30watt solar panel. So at least there is some light outside when we have a power failure.

    Now I use 2 x 12v 7.2Ah batteries in parallel connected to the solar regulator. Now I used a few online calculators and even with one battery it should shine for 8 hours or so. I reckoned that 2 batteries would be more than enough to run it till the sun comes up. But after 2 hours or so the regulator shuts off the load. I had two old batteries that was still good, and then I went an bought two brand new one's, same result.

    Was my calcs wrong? Is the regulator faulty? Any suggestions? I will remove the bulb and do some testing without the regulator...
    Your Solar Panel is too small.

    LED Consumption 9W for 12 hours. 108Watts

    Battery capacity = 12 X 7.2 X 2 = 172 Watts, at 50% discharge 172 /2 = 86 Watts. So even at 50% discharge which will kill the batteries in no time if you use the system every night.

    Solar Panel 30 x 4 (that's a good day) 120 Watts.
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  9. #9
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    Default Re: Solar light question

    Let's do a conservative calc with batteries already charged up beforehand:

    9W @ 12VDC = 0,75A + losses in the LED driver, so say 1A draw.

    two x 7.2Ah batteries in parallel gives 14Ah of which only 50% is available, so say 7Ah.

    7Ah/1A = 7 hours

    Something is definitely wrong.
    Quite likely the controller switches off too early.


    On a good day the solar panel would deliver 1,6A for 5 hours = 1,6 x 5 = 8Ah (= 96Wh @ 12V).
    So, the 30W panel is too marginal, even on a good day.
    Still the charged batteries should drive the lamp for 7+ hours easy.
    Eggie.

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  10. #10
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    Default Re: Solar light question

    Thanks for the info guys, okay now at least I know the batteries is sufficient, the panel not...would a second 30 watt panel be enough?

    I will test current draw tonight.

    Regarding the other question, it's not a day night bulb, but the regulator has a setting to turn on the load 1 hour after dark and off as soon as it detects sunlight on the panel.
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    Default Re: Solar light question

    Quote Originally Posted by staalwol View Post
    Thanks for the info guys, okay now at least I know the batteries is sufficient, the panel not...would a second 30 watt panel be enough?

    I will test current draw tonight.

    Regarding the other question, it's not a day night bulb, but the regulator has a setting to turn on the load 1 hour after dark and off as soon as it detects sunlight on the panel.
    Yes, but a 5W LED will save you an awful lot of hassle and costs
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  12. #12
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    Default Re: Solar light question

    Quote Originally Posted by Fluffy View Post
    Yes, but a 5W LED will save you an awful lot of hassle and costs
    Now that is a very good point! Hopefully I won't loose to much light output, but for the cost of a 5w bulb compared to another panel...I will do a test. Then I will only use 1 battery I assume?
    "The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts" : Bertrand Russell

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  13. #13
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    Default Re: Solar light question

    I've run a radio transceiver off a 7AH battery for almost a day......I cannot understand your problem with a 9W light.
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  14. #14
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    Default Re: Solar light question

    Sorry double post
    Last edited by staalwol; 2018/07/17 at 02:36 PM.
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  15. #15
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    Default Re: Solar light question

    Okay, bit of feed back, the calculations was luckily correct, and it was indeed the solar controller. Replaced it with another one I had laying around, and whalah! Light was on right through the night till morning.

    Thanks for all the advice guys!
    "The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts" : Bertrand Russell

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  16. #16
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    Default Re: Solar light question

    5W LED is still a lot of light. I have made up a similar setup just to have some light in my driveway in case of mains failure - no solar panel, just a single 12V 7Ah battery, 12V daylight switch, alarm system charger and 220V relay.
    ZS6VL


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