Everlasting Solar Camping Night Lite

http://www.ledlights.greenwatts.info/ This simple project converts two solar garden lites and some PVC thin walled central vacume pipe into a pocket sized LED solar powered lamp that can be used as a night/comfort light or reading lamp. The finished lamp is water proof, will float and will last virtually forever and cost under $10 to make.

The circuit uses two NiCd AA batteries in series which under-drives the LED array giving off enough lite to be usable but consuming very little power. The batteries will last for thousands of recharges, the LEDs are rated for over 100,000 hours and the solar cells last over 20 years.

Disasemble the solar garden lites we are going to use the solar cells, the NiCd AA baterries and one of the Schottky diodes that you will find on the little circuit board. The solar cells may be glued into place but you should be able to carefuly free them. We will also need some wire, a small resistor and 12" of central vacume pipe. For tools you will need a utility knife, 20watt soldering iron, and small screw driver. You will also need clear silicone, PVC cement and super glue. http://www.ledlights.greenwatts.info/

Cut two 150mm/ 6inch sections of the PVC pipe using a fine toothed saw then make a deep score along each length of pipe with a utility knife. If you compress the pipe the plastic will break at the score mark down the length of each pipe section. http://www.ledlights.greenwatts.info/

Heat each section of pipe in an oven at about c/f - 125/225 degrees until the plastic becomes pliable. It will be fairly hot so gloves are recommended. Remove from the oven and press between two flat surfaces. If the plastic curls after pressing and cooling repeat the process. Be careful not to over heat the plastic. http://www.ledlights.greenwatts.info/

Referring to the dimensions on the plans (goto http://ledlights.greenwatts.info/led_light_lamp_plans.htm for the Camp Lite plans) layout and cut all the required plastic pieces. The plastic is very easy to score and break to produce very accurate and strait edges. Use pliers to break away smaller peices.

To make the cutouts for the solar cells we need to heat the plastic as in step 2. Use a sharp pencil to mark the cut outs which will be 48mm x 48mm spaced 5mm apart and 5mm from each edge. Heat the plastic and first cut each corner then using a strait edge cut out the two openings. You may have to reheat the plastic for each cut depending on how quick you are. When finished cutting reheat the plastic and press flat. The resulting frame should overlap each edge of the 50mm x 50mm solar cells by 1mm. An alternative method is to first cut the two openings in a larger piece of plastic then trim the outside to the final dimensions...

Mark guide lines onto the bottom of the plastic frame and mount each solar cell using silicone. A good method is to align and tack the cell let it dry then finish applying the silicone and set aside to dry. When cured the silicone should provide a water tight seal.

Layout and drill the holes for the twelve LEDs on the front panel piece. Following the dimensions on the plans. Center punch each hole with a punch or nail. First drill a small pilot hole at each punch mark then drill out to the final 5mm size. Also drill out two holes on each end of the 10mm overhangs.

Drill a 5mm hole in the center of an end panel for the switch. Cement the 5mm spacers to the inside of the end panel then secure the switch with silicone and let dry. Do not cover the electrical contacts with silicone.

Cement the rest of the spacers on all of the panels removing any globs of cement and also checking for a good bond when dried. Applied properly PVC cement melts the plastic and creates a very strong bond when cured.

Assemble the two side, bottom and back panels using cement and let dry. Make sure the panels are square to each other by using a square wood block and a flat surface. Place the larger panel on the flat surface, apply cement to the smaller panel and place into position hold the smaller panel square against the wood block. PVC cement dries fairly quickly and will hold after about 60 seconds. Cement small spacers into each corner.

Insert the 12 LEDs into the front panel paying attention to proper polarity. If the LEDs are new the leads should be cut to about 8mm and bent outward at the ends. Place a small dab of super glue around the base of each LED on the inner surface of the front panel.

Solder the negative and positive leads to the LEDs. First cut the positive wire a few inches longer then the row of LEDs, strip the plastic off the wire and give the wire a quick sanding. Tin each positive LED lead and solder the positive lead wire to all of the positive LED leads.

Make the negative lead wire twice as long as the row of LEDs and strip half of the plastic off of the wire. Lightly sand the bare wire, tin all of the negative LED leads and solder the negative lead wire to all of the LEDs.

Trim the positive lead and solder the resistor into place, (I used four 10ohm 1/4 watt resistors in parallel to give me a 2.5ohm but I do not think the exact value is critical so anything from 2 to 6 ohms should do fine) connect a lead to the other side of the resistor. Solder a short lead and the Schottky diode onto one side of the switch making sure of the correct polarity. See picture. Make sure to place shrink tubing onto the leads to cover the connections.

Cement the front panel assembly into place and add the small spacers to reinforce the corners.

Using a 3" piece of bare 12 or 14 gauge copper wire we are going to attach the two NiCd batteries. First using a fine sandpaper clean off both the positive and negative battery contacts and clean the ends of the copper wire. Tin both the battery contacts and the wire ends as shown then bend the wire into a half circle and solder to the positive terminal of one battery and the negative terminal of the other. Let the solder harden and then twist the batteries into alignment.

Seal all the seams between all the assembled panels of the bottom assembly using silicone. We want to create a water tight seal.

Add a positive and negative lead to the two batteries as shown. Place the batteries into position and tack with silicone. Solder the positive battery lead to the center lead on the switch, solder the lead from the resistor to the last lead on the switch and protect all the connections with shrink tube.

Cover the entire switch body with silicone and seal the back of each LED with silicone. Carefully seal the switch hole in the side panel from the outside with a light coat of silicone making sure the switch can still operate.

Connect the two solar cells in series by soldering the negative lead of one cell to the positive lead of the other cell and protecting with shrink tube. Tape the wires to the back of the cells or tack them with silicone. Attach the positive lead of the two cells to the diode lead and protect with shrink tube. Connect the negative lead of the two solar cells to the negative lead of the batteries and the LEDs and protect with shrink tube.

Before cementing and sealing the top panel into place we need to test the circuit. Use the switch to turn on the LEDs and leave them on until the batteries are drained. When the batteries are almost drained the LEDs will dim at this point set the switch to the solar charging position and expose the solar cells to direct sun light for a few hours. If everything is working OK the batteries should now be at least partially recharged and the LEDs will shine at their regular brightness.

Place a bead of silicone along the top edge of the spacers on all four sides of the bottom assembly then carefully place the top frame with the solar cells into position. Gently and evenly press down on the edge of the top frame until seated. If the frame is not completely flat you can simply flip the whole assembly over and place some weight on it until the silicone cures.
Additional pictures (high res) available on http://www.greencamplite.info