DIY solar lamps

Recommendation points

• What parts and where is it better to order
• How much will the details cost
• We solder a simple circuit and arrange the details
• Luminaire design and assembly
• Some operating secrets

Many summer residents dream of decorating the view of a nighttime personal plot with portable solar-powered flashlights, but many simply cannot afford such a luxury. There is a way out: by collecting lamps with your own hands from inexpensive radio components, you can easily organize a real scattering of lights in the garden.

Purchased lamps are more often disappointing than pleasing. They shine dimly, work only a few hours and hardly last longer than two years. When assembling a garden lamp with your own hands, you yourself determine the necessary parameters and you can count on a guaranteed result.

The principle of operation of such a lamp is very simple. During the daytime, the sun hits a photocell, which generates electricity and charges a small battery. When the solar panel voltage drops, the transistor switch cuts off the current from the solar panel to the battery and supplies power to one or more bright LEDs. When voltage appears on the contacts of the photocell, reverse switching occurs.

What parts and where is it better to order

The most difficult to get hold of solar cells. Substandard items will do; the easiest way to buy them is from various online auctions such as Aliexpress. Choose a module with an output voltage of at least 5 volts, the power should correspond to the number of LEDs. It is very important that the module has conductor taps, otherwise buy those that come with flat conductors and a flux pencil.

The most expensive element in the luminaire is a nickel-metal hydride or lithium-ion battery. We need rechargeable batteries with a voltage of 3.6 V, they look like three finger batteries wrapped in a film. The capacity should also correspond to the total power of the LEDs multiplied by the number of hours of battery life + 30%. You can buy together with the modules.

Light sources are LEDs. Based only on the characteristics, you most likely will not be able to find the appropriate level of illumination, so you will have to choose empirically. BL-L513 bright white LEDs are recommended. They are easy to find in electronic component stores, for example, in “Chip and Dip” they cost 10 rubles each. Each LED requires a 33 ohm current limiting resistor.

Also, for each lamp you need a 2N4403 transistor, a 1N5391 or KD103A rectifier diode, as well as a resistor, the value of which is calculated by the formula R = U_baht x 100 / N x 0.02, Where N Is the number of LEDs in the circuit, and U_baht – battery operating voltage.

How much will the details cost

In cheap Chinese lamps costing about 500 rubles. only one LED is used, which is clearly not enough. What’s more, the battery voltage is 1.5V, which is why the light is very dim.

In order not to waste time in vain, it is recommended to assemble luminaires with the optimal configuration, which includes:

The elements	Price	Qty	total cost
Solar modules Eco-Source 52×19 mm	RUB 675 for 40 pcs. (for 4 lamps)	1 set.	RUB 675.00.
SONY HR03 battery (1.2V 4300mAh)	885 RUB for 12 pcs. (for 4 lamps)	1 set.	RUB 885.00.
BL-L513UWC LEDs	RUB 10 / pc.	12 pcs.	RUB 120.00.
Resistor CF-100 (1 W 33 Ohm)	US $ 1.8 / piece.	12 pcs.	21,60 rub.
2N4403 bipolar transistor	RUB 6 / pc.	4 things.	24,00 rub.
Diode 1N5391	RUB 2.5 / pc.	4 things.	10,00 rub.
Resistor CF-100 (1 W 3.6 kΩ)	US $ 0.90 / piece.	4 things.	7.60 rub.
Total:			1743.20 rub.

It turns out that to assemble one high-quality lamp, you need about 435 rubles worth of components. But from the same parts, having bought the last 3 items, you can make 12 analogs of cheap Chinese lamps.

We solder a simple circuit and arrange the details

To assemble such a circuit, it is not necessary to have a textolite base and etch the tracks. The cathodes (short leg) of all LEDs are assembled into one unit, 33 Ohm resistors are soldered to the anodes (long leg). The tails of the resistors are also soldered together and soldered to the collector of the transistor. A 3.6 kΩ resistor is connected to the base of the transistor, and the cathode of the rectifier diode is connected to the emitter. The anode of the diode is connected to the base resistor, and the positive pole of the solar modules is fed to the same node. The minus from the modules and the battery is connected by wires to the combined cathodes of the LEDs. The positive pole of the battery connects to the emitter of the transistor.

Luminaire wiring diagram

Individual solar modules have a voltage of 0.5 V, while charging the batteries requires 4.5–5 V. Therefore, individual modules must be combined into chains. First, solder the conductors to the modules if there are none. To do this, cut the flat conductor into strips slightly longer than the width of the module. If the module is 19 mm, cut by 25 mm.

The positive contact of the module is located on the back, and the negative is the same central strip on the front. On this strip you need to run a flux – this is such a colorless marker from the kit. Then a piece of conductor is laid over the contact. It remains only to slowly draw a soldering iron from above: a thin layer of tin is already on the conductor. The remaining tail is soldered to the contact on the back of the next module and so on along the chain until 10 modules are assembled in two rows.

Between the rows, you need to make a jumper from a flat conductor, and solder thin copper wires to the remaining two ends. Be careful when working with modules, they are very fragile. It is also not advisable to overheat them, so do not keep the soldering iron in one place for too long..

Luminaire design and assembly

The lamp needs a housing, preferably waterproof. It is very convenient to use an empty canning jar with a screw cap.

Part layout example

To assemble such a luminaire, you need a piece of plywood to glue two rows of modules onto it. The proposed photocells have a size of 52×19 mm, folding them in two rows, you get a rectangle with dimensions of approximately 110×110. You can glue the modules on double-sided tape for mirrors, but do not press down too hard.

Before sticking the modules, cut a hole in the center of the board for the lid of the can and fix it inside with a couple of drops of hot glue. In the cover, you need to pierce two holes for entering wiring from the modules, do not forget to restore the tightness later.

To conveniently place the electronics inside, glue a small foam washer to the inside of the cover. If, when soldering the circuit, you do not bite the legs, you can stick the elements into the foam and fix them so. And if you make rectangular cuts in the foam, you can easily insert batteries into them. For contact, use a pair of flattened aluminum foil balls with wires soldered to them.

Warm the inside of the jar well with a hairdryer before closing the lid. So the parts will oxidize less, and condensation will not appear on the walls of the can..

Some operating secrets

Luminaires do not tolerate cold very well, so it is advisable to bring them into a warm room for the winter. The batteries must be fully discharged by covering the solar panel with something opaque. Wrap the batteries separately in paper, which will last longer. Also consider covering the modules with a transparent protective cover or using film photocells. In general, such lamps are enough for 6-7 years of active use..