Simple Solar Circuits : 11 Steps (with Pictures) - Instructables

Each spring I gather solar lights my neighbors tossed in the garbage after the lights have stopped working. The ones that only need minor repairs, I repair, and the ones that need major work I strip for parts and reverse engineer the circuit boards. Most of the circuit designs used in automated decretive garden lights are simple and easy to reverse engineer.

You can find more information on our web, so please take a look.

https://www.instructables.com/id/Reverse-Engineering-1/

Although it can be more work, I repair the solar cells.

https://www.instructables.com/id/Repairing-Polymer-Degradation-on-Solar-Cells/

https://www.instructables.com/id/Repairing-Solar-Cells/

Garden lights incorporate three basic circuits, the charging circuit, the dark detecting circuit that turns the LED driver on and off, and the LED driver. Some LED drivers incorporate a voltage multiplier or voltage booster in the LED driver circuit since 1.2 volts is insufficient to power the ultra-bright LEDs.

Now to get started adding solar power to your small electronics projects and use the sun to power your battery powered night lights, garden lights, and other automated decorations or projects. The circuits are easy to build and to get working. They are fun to build and to teach your kids, how to work with light.

In the last step I control a 5 volt motor with a 1.2 volt battery and the solar light IC.

Most of the circuits in this Instructable work as long as you are in the ball park so it is easy to substitute parts and get the circuits to work.

Transistors; just about any general purpose low power transistor, can be used for these circuits.

2N, 2N, 2N, S, S, BC546, BC547, or similar NPN transistor

2N, 2N, 2N, S, S, BC556, BC557, or similar PNP transistor

Diodes; just about any general purpose, switching or other low power diodes, can be used for these circuits, however Schottky diodes have lower voltage drops and work very well.

1N to 1N series, 1N914 to 1N series, and 1N to 1N series.

Resistors; you will need an assortment of resistors for these circuits most of them only need to be ¼ watt, once in a while depending on the circuit you build a ½ watt resistor for circuits over 3 volts. The resistors do not need to be exact so if the schematic calls for a 50Ω resistor, a 47Ω or a 51Ω resistor will work. There is a lot of room to play in these circuits.

50Ω, 100Ω, 150Ω, current limiting resistors for the LEDs.

1kΩ, 2kΩ, 5kΩ, 6.8kΩ, 10kΩ, 15kΩ, 22kΩ, 47kΩ, 100kΩ, 1MΩ, most of these resistors you will only need 1 resistor of each for a circuit but it is always nice to have extras.

Photo Resistor, if you salvage garden lights like I do you should have plenty.

1 ultra-bright LED more if you are doing more than one project, colored LEDs if you like, just for fun and children like pretty colors.

1 switch

Assorted batteries and holders

Assorted Solar Cells

1 bread board for testing.

1 multi meter

Capacitors; a must for the voltage multipliers.

1.2nF, 100pF, one of each.

Inductors

Two 0.47mH

One 22mH

If you make the circuits in the garden light IC datasheet you will need the parts listed in the datasheets.

The first part of a solar circuit is the solar cell or other device for collecting light and making use of it; I have quite a collection of solar cells and solar panels, most of them salvaged from solar garden lights rescued from the garbage. Many of them were repaired by me and they range from 1.5 volt solar cells to 6 volt solar cells and 20 mA to over 100 mA.

Now that you have solar cells it is time to find out what you can do with them. You do this by checking the voltage and the amperage produced by the solar cell. On a good sunny the best as you can get, adjust the cell as close to a 90⁰ angle to the sun. Just a small cloud across the sun, or the cell not facing the sun at a 90⁰ angle can affect the cells output.

Never check the voltage or the current of the solar cell unloaded, that means do not just attach meter leads to the solar cells leads. Unloaded the meter misinterprets the current going through it as voltage and gives you a much higher voltage than the solar cell is producing.

Start by connecting the solar cell to a resistor, the resistor can be any size. I chose a 51Ω resistor because I wanted to use the same resistor for checking the current. Then measure the voltage across the resistor, now you get a much more accurate output voltage between 1.5 to 3 volts.

Next test the current; it is always good practice to never test a power source’s current without a load, dead shorts tend to be detrimental to electronics. With the 51Ω resistor attached to my circuit I got a fairly accurate current of 25 to 65 mA.

Solar cells are less affected by dead shorts; most solar cells convert less than 8% of the suns energy to electricity. If you dead short a battery the current will climb until something blows, if you dead short a power supply the current will climb until something blows. With a solar cell if you connect the amp meter to the cell without a load, the current will climb like a battery or a power supply but the current will stop climbing once it reaches 8% of the energy of the sun. That doesn’t mean this is safe to do in all cases, just some solar cells will not be damaged by it.

Since the solar cells were salvaged from solar garden lights most fell into two groups; 1.5 volt and 3 volt cells, however in the two groups the currents varied, 25 mA, 35 mA, and 65 mA.

Now you have the basic specks of the solar cells it is time to look at the batteries that are charged by these solar cells. The batteries come in 1.2 volt NiCads with a capacity of, 200 mAh, 300 mAh, 600 mAh and mAh.

When you match the battery to the solar cell all you need for a charging circuit is a diode. To charge the high capacity of a NiCad battery or battery pack it is recommended to charge the battery at the rate listed on the battery label. But when you don’t have these instructions follow the C/10 charging rate.

To achieve a complete charge of a NiCad battery it must be charged at a rate equal to or greater than C/10. Where C = cell capacity in mAh. For example: A mAh cell requires /10 or a minim 100 mA charge rate or greater. Charging at a lower rate than C/10 will not result in a completely charged battery.

http://www.powerstream.com/NiCd.htm

Although a current-limiting resistor between a solar panel and a battery is technically needed, it is not necessary if the battery will not be overcharged. In our case, the solar cells will not overcharge the battery. These solar cells should be able to charge one 1.2 volt, battery, or two 1.2 volt batteries in series at a rate of 20 mA for 200 mAh battery, 30 mA for a 300 mAh battery, or 60 mA for a 600 mAh battery.

The charging circuit for these batteries is simple, a solar cell connected to a diode then connected to a NiCad battery. The diode isolates the batteries from the solar cell so that when the sun is not out the solar cell will not drain the batteries.

You can use almost any switching diode for this circuit, and you can use a much more efficient circuit with a lower voltage drop than a diode, but you would be hard pressed to do it with the same ease or price as a 1N schottky barrier diode.

Dark detecting LED driver circuit, to add darkness detecting capability to a solar circuit is easy, because the solar panel can directly serve as a sensor to tell when it’s dark outside. To perform the switching you need a diode between the transistors base and its emitter, (PNP Transistor) or the collector, (NPN Transistor). The diode isolates the base of the transistor from the batteries so only the solar cell powers the transistors base.

In this circuit I use a PNP transistor as Q1 that is controlled by the voltage output from the solar panel. When it’s sunny, the output of the solar cell is high at the transistors base, which opens the transistor and switches off the LED.

When it gets dark; the solar cells voltage drops to zero, the current flows out the transistors base and through the solar cell to ground, this closes the transistor letting the current flow through the LED switching it on.

This circuit works very well for low power applications when there in not enough current coming out of the base to damage the solar cell. However with circuits that produce higher currents coming out of the PNP transistors base, you can burn out the solar cell.

With higher currents you do not want the current passing from the base of Q1 through the solar cell or you risk burning out the solar cell. When you use a NPN Transistor the current travels from the solar cell to the base of Q1.

Link to ygne

This circuit uses the solar cell for dark detection, this charges the batteries and turns the LED on when the solar cell is in the sun, or turns off the LED when the solar cell is in the dark not charging the batteries. When the solar cell is producing power, the power is applied to the base and the collector of Q1, the transistor switches to closed, and lights up the LED. When the solar cell is in the dark and not producing power, no power reaches Q1s base and the transistor is open turning off the LED. This is a good charge indicating circuit however it doesn’t make a good nightlight since the sun must be out to light the LED.

This circuit is the LED driver using a NPN transistor, when the switch is closed power goes to the base and the collector of Q2 lighting up the ultra-bright LED. When the switch is open no power gets to the circuit and the ultra-bright LED is off.

When you combine the LED driver circuit without the charge indicating LED and the dark detecting circuit; the ultra-bright LED will come on when the solar cell is not charging the circuit. Now when light is on the solar cell it powers the base of Q1 closing Q1 and reducing the voltage to the base of Q2 to near zero volts opening Q2 and turning the ultra-bright LED off. When the solar cell is in the dark there is no power to the base of Q1 opening Q1 and increasing the voltage to the base of Q2 closing Q2 and turning the ultra-bright LED on. Now you have an automatic on and off light.

This circuit has one disadvantage, if you miss calibrate R1 and R2 the ultra-bright LED can come on with a very low drop in sunlight, or only come on in total darkness. To calibrate the light level the ultra-bright LED turns on and off, adjust the value of R1 up or down until the ultra-bright LED changes state at the desired light level.

This circuit is a little different than the circuits that use the solar cell for a dark detection; this circuit uses a photo resistor for the dark sensor in place of the solar cell. Now the diode is placed right after the solar cell so Q1 and Q2 are powered by the battery. The advantage of this circuit is the dark sensing LED driver can be one location and the charging circuit with the solar cell can be in another location.

The value of R1 changes with the light, its value goes down as the amount of light goes up and its value goes up as the amount of light goes down. This action of R1 varies the power applied to the base of Q1 and allows Q1 to control the ultra-bright LEDs on and off cycle.

Since the value of R1 changes with light and R2 is fixed, to calibrate the dark sensing circuit you adjust the value of R2 up or down to adjust the light level that turns the ultra-bright LED on or off.

To switch Q1 from a NPN transistor to a PNP transistor you need to swap R1 for R2 and R2 for R1 for the circuit to function as an automatic light.

Solar garden lights are one of the best investments for your outdoor space, except when they stop working.

Several reasons may be behind your solar lights not working. We will go through the things you should do to get them working again.

In some cases, you may have to replace your solar-powered lights altogether. Either way, by the end of this quick guide you will know what you need to do. So, let’s get straight to it!

10 Things To Do If Your Solar Lights Stop Working

If your solar-powered lights stopped working, there are 10 easy things you can do to check whether they’re faulty or they just need some settings adjusted.

The 10 steps you need to take to fix your solar lights are the following:

1. Check whether your solar lights are turned on
2. Check that there’s not a pull tab on the battery
3. Cover the solar panel to test the light output
4. Ensure the solar panel is clean
5. Make sure the solar panel is positioned in a sunny spot
6. Test the solar light with regular batteries
7. Switch the solar light off and leave to charge for 48h
8. Check the weather conditions during daytime
9. Try a different lighting mode
10. Contact the retailer 

Check whether your solar lights are turned on

The first step you need to take when your solar lights stop working is to check whether they are turned on.

Many people don’t realize that some solar lights have an on/off switch. If that’s the case with your solar lights, make sure that the lights are switched on.

Check that there’s not a pull tab on the battery

When you buy a brand new solar light, you should always check the battery inside the solar panel. The reason for this is because in some cases there is a pull tab on the battery that needs to be removed before the light will function.

If your solar light is brand new, make sure to check this step before you look into other possible problems.

Cover the solar panel to test the light output

Almost all solar lights charge during the day and they only light up at night time. Therefore, to test whether your solar lights are working, you need to cover the solar panel to simulate darkness.

If you completely cover the solar panel and the solar lights start working again, then there may be a nocturnal lighting source near your solar light that is decreasing its efficiency.

If your solar light is still not working in the absence of light, then proceed to take the steps below.

Ensure the solar panel is clean

One of the most common reasons why solar lights stop working is a dirty solar panel. A dirty panel can impact the amount of charge received.

Simply wipe the solar panel off with a clean, damp towel. Then, you can cover the solar panel briefly to check whether the solar lights work again.

Make sure the solar panel is positioned in a sunny spot

A well-positioned solar light is as important as having a clean solar panel. If your panel isn’t positioned correctly, it might not be receiving enough charge.

The solar panel should be positioned in a sunny spot to receive sunlight most of the day. Make sure to avoid big shadows or any spots in your garden that don’t get enough sunshine.

Test the solar light with regular batteries

A possible reason for your solar lights not working properly is the batteries that you’re using. The solar batteries may not be receiving enough charge or they are not holding it.

If the solar lights work with regular batteries then the problem is either with the rechargeable batteries or the solar panel. If that’s the case, you should replace your existing batteries with new rechargeable batteries. 

If your solar lights are still not working, then the solar panel is probably faulty.

Read more: Do solar lights need batteries?

Switch the solar light off and leave to charge for 48h

During rainy months, it might take longer for your solar lights to get a full charge. This could be the reason why it seems like your lights stopped working. 

In this situation, you should switch the solar light off to leave it to charge completely for 2 to 3 days. Then, switch it on and see if it works again.

If this step is successful, it is recommended that you repeat this process every few weeks during the winter months.

Check the weather conditions during daytime

If you’ve tried all the steps above and your solar lights aren’t working still, there is something else you can do to fix them.

Since solar lights rely heavily on sunlight to charge effectively, you need to check the weather conditions during daytime to evaluate whether the solar lights receive enough sunshine.

Just look at your solar lights at around midday and check whether they get any sunlight at all. If not, try to move them around to a place that has more favorable weather conditions.

Ultimately, if your solar lights still don’t work it might be due to their low quality when it comes to solar power absorption. If that’s the case, you need to consider investing in higher-quality solar garden lights.

Read more: Do solar lights work in winter?

Try a different lighting mode

The last thing you can try to fix your solar lights is to try a different lighting mode. 

If your solar light has several lighting modes, you can try to switch to a less demanding mode when it comes to battery consumption. For example, a synchronized white lighting mode uses less charge than a still color-changing mode.

Though this is only a temporary fix if it works it means that your solar lights aren’t getting enough sunlight. In that case, you can try to move the lights around in your outdoor space to find the spot with the biggest amount of sunlight.

Contact the retailer

If none of the steps above worked, the last thing you can try is to contact the retailer.

Try to gather as much information as possible about your solar lights and contact the retailer directly by or . 

At OutdoorLights, we offer a 1-year warranty on all our solar lights and if you experience any problems with your solar lights, one of our lighting specialists will be happy to help you to identify any possible issues with your solar lights. 

If this free-of-charge advice doesn’t fix the problem, you will get another solar light for free.

Why do solar lights stop working?

There are many reasons why a solar light might have stopped working.

The most common reason why solar lights stop working is because of the absence of sunlight. If your solar garden lights don’t receive enough sunshine, they won’t charge completely. Consequently, they will stop working after a few days or weeks.

Other usual issues with solar lights include dirty solar panels, poor light placement, and using unsuitable batteries.

Learn More About Solar Lights

Whether you own a low-quality Costco solar light or a high-tech solar umbrella light, it can be challenging to identify the exact reason why your solar lights stopped working. That’s why we offer you free advice from one of our lighting experts.

If you need to replace your existing solar lights, feel free to check out our premium range of high-quality solar lights. At OutdoorLights, you can find the world’s leading outdoor lights, from garden party lights to outdoor security lights.

If this blog post has answered your question or if you would like to learn more about all things related to outdoor solar lights, visit our lighting blog.

Are you interested in learning more about Small Solar Light Towers? Contact us today to secure an expert consultation!

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