Introduction: Add-on LEDs for Solar Day Lamp

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This project is proposed for enhancing the utility of Solar Day Lamp which was published earlier in Instuctables:

https://www.instructables.com/id/Simple-Solar-Day-L...

In the proposed project, two additional arrays of small LEDs are connected to the solar panel. These add-on LED arrays are designed to draw less than 0.5 W power, so that the light intensity of main white LED array is not reduced significantly. This add-on scheme offers additional features which are explained in detail in this article.

Fig. 1 shows the circuit diagram of the proposed scheme. The original Solar Day Lamp circuit is enclosed in dashed lines. Two more LED arrays consisting of LED6 to LED9 and R2 plus LED10 to LED13 and R3 are connected to the PV Panel. These are low power yellow color LEDs. The resistors R2 and R3 limit the current flowing through these LEDs. The step by step construction procedure is given below.

Material: Following material is needed for making the add-on LEDs (see Fig. 2)

  1. Brass oil lamps, 2 pieces
  2. Yellow color square LEDs, 8 pieces
  3. 1 inch by 1 inch general purpose PCB, 2 pieces
  4. Screw, Washer and Nut, 2 sets
  5. Resistor 680 ohm 0.25 W, 2 pieces
  6. Wires

Note: Above list of material is only for the add-on lamps. For Day Lamp, please check the link above for the list of material required.

Step 1:

The brass oil lamp shown in Fig. 3, has 1.5 inch diameter and 2 inch height. In the middle of this lamp, a wick holder is present. Remove the wick holder by turning it anticlockwise. The screw selected should have the same pitc h as wick holder as shown in Fig. 3. Select the screw length such that it just proj ects out at the top rim.

Step 2:

Take a general purpose PCB and make two square pieces. The diagonal of these PCBs should be slightly smaller than the inner diameter of the brass lamp. Make a hole at the center of these PCBs as shown in Fig. 4. Mount 4 square LEDs at four corners of the PCB. Mount the resistor and the connecting links as shown in the figure.

Step 3:

Cut wire into two pieces. The smaller piece of wire is used to connect between the two lamps. The longer wire is to be used to connect from the lamps to the main white LED array. Solder the smaller wire to one of the PCBs. Then connect the longer wire along with smaller wire to the second PCB as shown in Fig. 5. Fix screws to the PCBs and then tie a knot of the wire to the screws to avoid wire getting cut from the PCB during handling.

Step 4:

Fix the two PCBs on the lamp. Take the longer wire and connect it to the white LED array with correct polarity. The add-on feature for the Solar Day Lamp is ready as shown in Fig. 6 and Fig. 7.

Step 5:

Put a plastic cap on the LEDs to avoid dust getting collected on these LEDs.

Step 6:

  1. The forward voltage of white LEDs is about 3 V. Therefore for white LEDs to turn ON, PV panel has to develop about 15 V. The forward voltage drop of yellow LEDs is about 2 volts. Hence, for turning ON 4 LEDs, the solar panel has to develop voltage greater than 8 volts. Therefore these lamps will turn ON much earlier in the morning. Also, these will remain ON for a longer time in the evening. Hence the duration for which yellow LEDs will remain ON is much longer in the day.
  2. On rainy days, the white LED array may not provide sufficient light. However, the yellow LEDs will be ON rainy days too. Thus the utility of Solar Day Lamp is enhanced.
  3. This is a better substitute for candles and oil lamps. Candles and oil lamps are expensive, burn fuels and produce indoor air pollution. Solar energy is purest form of energy and is available freely.
  4. Light intensity can be increased by reducing the value of resistors R2 and R3. Care must be taken not to reduce the value below 330 ohms to avoid excess current flow through LEDs.
  5. This lamp can be used without Solar Day lamp, by supplying power using a 12 V adaptor.

Solar Day Lamp is used where ever there is less light during day time. The add-on LEDs can be used in Pooja rooms in front of deity, in front of photos, idols etc. in place of candles and oil lamps. This is a greener alternative.

Abhijeet Deshpande