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I need some help with a solar light project

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onesojourner

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I am trying to come up with a scale ablesolar light design.


For my initial project I am going to use some 12v LED strip lights. I should preface this with I have very little idea what I am doing. Provided my test was correct these pull .05 amps. Does that sound right? I want this light to come on at night automatically. I am not sure how I want it to shut off but I am leaning towards it shutting off at a set battery voltage to avoid damage to the battery. Does that sound reasonable? I want a minimum runtime of 4-6 hours. I have a 18ah SLA for initial testing but I would like to use something that is more appropriate. I have also have several 18650s but I think that may be overly complicated.


I have a few bits that may come in useful for this project. I would like to use these where possible.


  • Solar Panel 2.5W 5V/500mAh (x2)

  • Solar Panel 12V 3W

  • XL6009 DC-DC Booster Power Supply

  • Max DC-DC XL4005 Step 5A Down Adjustable Power Supply

  • Boost Buck DC-DC Adjustable Step Up Down Converter XL6009

  • Smart Electronics 5V Micro USB 1A 18650 Lithium Battery Charging Board With Protection Charger

  • Various Diods

  • Various Resistors

  • Various Capacitors

  • Photo Resitors

  • N-Channel MOSFET 60V 30A

  • P-Channel MOSFET 60V 27A

  • Voltage Regulator - 12V COM-12766 ROH basic L7812

  • Arduino Uno

I am still looking a for a nicely done diagram to base this project on, but so far I have been unsuccessful. If someone has something that would get me going in the right direction I would greatly appreciate it. I am unsure if I will need any kind of charge controller for this kind of small setup.
 
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spec

Well-Known Member
Most Helpful Member
Hi OS,

Welcome to ETO. Which State are you from: if you enter it next to 'Location' on your user page it will display in the window at the left of your posts.

I haven't done a circuit for you, but just to let you know that your project seems quite feasible using the parts that you have. I will give your project some thought, as will the other ETO members no doubt.:)

spec
 
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spec

Well-Known Member
Most Helpful Member
Here is an initial analysis and a recommended configuration for your proposed system:

(1) ENERGY CONSUMPTION
(1.1) The LED string consumes 12V * 50mA = 0.6W
(1.2) You would like to power the LED string for 6 hours per 24 hour day, so the LEDs will consume 6 hours * 0.6W = 3.6 Watt/hours (W/h) per day.

(2) ENERGY STORAGE
(2.1) Assuming your 18650 Lithium Ion (LiIon) batteries each have a 2A/Hr capacity (2,000 mA/h), each battery can store 3.6V * 2A/h = 7.2 W/h of energy.

(3) ENERGY SOURCE
Assuming that you get 4 hours sunlight a day- only a very rough estimate which will be pessimistic if you live in Florida and optimistic if you live in Alaska.:p
(3.1) The 12V 3W solar panel will produce 4 hours * 3W = 12 W/h each day.
(3.2) The 5V 2.5W solar panel will produce 4 hours * 2.5 Watts = 10 W/h each day.

(4) SUGGESTED SYSTEM
(4.1) One 18650 battery which will store sufficient energy to power your LED string for (7.2 W/h)/ 0.6W = 12 hours.
(4.2) Say the 12V solar panel, but one of the 5V solar panels would do, if you prefer.

The suggested system passes the acid test because the energy input and energy storage are greater than the energy consumption.

You may ask why I have suggested a LiIon battery and dismissed the lead acid battery:

(1) The lead acid battery has an energy storage capacity way in excess of your needs at, 12 *18W/h = 216 W/h.
(2) A LiIon battery is much easier to charge and and has a far better defined cut off voltage.
(3) A LiIon battery maintains its charge much longer
(4) LiIon batteries are smaller and much lighter for a given energy storage
(5) The charging efficiency of LiIon batteries in much higher than lead acid batteries.
(6) You can use much more of the stored energy
(5) I do not like lead acid batteries (but they are necessary in some applications).:D

Give the suggested system above some thought and let us know if it fits in with your plans.

The rest of your requested functions: charging, battery cut off voltage, automatic switching on and off of the LEDs, etc can then be sorted at the detailed design stage.

spec
 
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onesojourner

New Member
This does indeed fit my plan. I have a clear view of the southern sky so I think on most days I will get significantly more sunlight. I am not sure how cloudy days will effect this but we do get quite a few of those in the winter so adding a bit of extra capacity would probably be a good idea. The batteries I have are TrustFire 18650 3.7V 2500mAh. So maybe 2 or 3 of those?

I am also fine with not using the lead acid battery. I would prefer to learn how to integrate the lithium batteries.
 

spec

Well-Known Member
Most Helpful Member
This does indeed fit my plan.
That is good. :)

I have a clear view of the southern sky so I think on most days I will get significantly more sunlight. I am not sure how cloudy days will effect this but we do get quite a few of those in the winter
We can probably get the average sunlight figures for Springfied.

so adding a bit of extra capacity would probably be a good idea.
You can add as many batteries as you like.:)

The batteries I have are TrustFire 18650 3.7V 2500mAh.
Bad language not allowed on ETO.:D


I am also fine with not using the lead acid battery. I would prefer to learn how to integrate the lithium batteries.
That's good too.

Thanks for prompt and specific replies- it is a great help for us.:)

spec
 
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audioguru

Well-Known Member
Most Helpful Member
A Chinese battery with "Fire" in its name is probably a fake one. Buy a Namebrand good one instead.
 

spec

Well-Known Member
Most Helpful Member
Some info about Springfield Mo sunshine: https://www.currentresults.com/Weather/Missouri/annual-days-of-sunshine.php

As you said, looks like there are quite a few days without sunshine!

I just reread your original post and you say "some LED strings", rather than, 'one LED string', as I thought. Could you say the maximum number of LED strings you want- it has a major impact on the design?

In view of the number of days without sunshine and, depending on how many LED strings you want, and how important it is to have the LED strings on every night, the lead/acid battery may not be overkill after all.:eek:

Another aspect is temperature:
Will the batteries be at the ambient outside temperature, because in Springfield MO the temperature goes below freezing point: -6 deg C, typically, in winter. This would not be a problem for lead/acid batteries but LiIon batteries should not be charged below 0 Deg C. http://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures

spec
 
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onesojourner

New Member
Some info about Springfield Mo sunshine: https://www.currentresults.com/Weather/Missouri/annual-days-of-sunshine.php

As you said, looks like there are quite a few days without sunshine!

I just reread your original post and you say "some LED strings", rather than, 'one LED string', as I thought. Could you say the maximum number of LED strings you want- it has a major impact on the design?

In view of the number of days without sunshine and, depending on how many LED strings you want, and how important it is to have the LED strings on every night, the lead/acid battery may not be overkill after all.:eek:

Another aspect is temperature:
Will the batteries be at the ambient outside temperature, because in Springfield MO the temperature goes below freezing point: -6 deg C, typically, in winter. This would not be a problem for lead/acid batteries but LiIon batteries should not be charged below 0 Deg C. http://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures

spec
Indeed. There are quite a few. I want to make sure that I don't damage the battery if we do have an unusually long stretch of cloudy days.

The LED string is 3 sections, and 9 LEDs total. The amps, .05 are for all 3 sections.

Now as far as the importance that this come on every night. It is not. This is just decorative. If there is a week in January that is really cloudy and the lights don't come on, no big deal.

Now, with that said I would like the knowledge to be able to scale this either to get more runtime out of this project or for a future project.
 

audioguru

Well-Known Member
Most Helpful Member
A lithium rechargeable battery is destroyed if it is discharged below about 3.2V. If you try to charge a lithium rechargeable battery that is below 3.2V then it will probably catch on fire. It is also destroyed and will probably explode and catch on fire (Lithium burns very hot) if it is charged above 4.20V. You need a circuit that disconnects the LEDs if the battery voltage drops below 3.2V and a proper Lithium battery charging circuit.
Maybe you should use a Ni-MH battery instead like solar garden lights.
 

spec

Well-Known Member
Most Helpful Member
Apart from the temperature limit of zero deg C for charging, LiIon batteries would be optimum. I have discharged many LiIon batteries below 3V without any explosions etc: bit dramatic AG. :D Taking any battery below a certain voltage, depending on the chemistry, is always bad for battery life though.

The charging voltage limit and cutoff voltage is not an issue, as this can be done quite simply in electronics, and max and min voltage levels apply to all battery technologies.

Don't worry about damaging your batteries OS, it really is not an issue.:)

spec
 
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