solarlamp

I bought some solar panels on eBay to repair some of my garden solar lamps but then used some of them to make my own solar lamps.

I am now on version 3 of my design.

This is my own design using a IRF9540N 100V P-Channel Power MOSFET and a LM317 adjustable 3−terminal positive voltage regulator instead of the usual YX8018 or YX8019 chips that a lot of people use. That allows you to use more batteries and LEDs for a brighter lamp. The costs are about the same as using the YX8018 or YX8019 chips. The IRF9540N and LM317 have a more rugged design and should weather better than the YX8018 or YX8019 chips. The 6 volt 110mm by 60mm solar panels are a good size to use with these lamps.

This is the circuit diagram for a solar lamp with four AA 1.2v batteries.

I've repaired some of my purchased solar lamps and have made a few new ones from scratch. The latest ones have stainless steel battery contacts. They work well and will not rust but they are very time consuming to make. You can buy a ready made battery battery container for about 1 GBP on eBay instead. Another alternative is to use springs from hand soap dispensers. Springs from cheap plastic cloths pegs also work well and will not rust. The stainless steel battery contacts I made were cut from an old Hotpoint dishwasher door. It's an ideal thickness. The sharp edges have been rounded with a grinding stone. The plastic was cut from an old ink jet all in one printer. You don't need heat sinks on the electrical components but it's nice to have in case you do something silly like shorting out the LEDs. The component legs can corrode so I've painted them with red primer. You can not solder on to stainless steel so they are secured with a screw and wire.

This is the circuit diagram for a solar lamp with a 3.7V LI-ION battery.

Note: For full battery charge use 780 ohm for R1 and 330 ohm for R2.

The LI-ION solar lamp is easier to make with only one battery. It's also cheaper because you can get these batteries for about 0.99 pence on eBay from China. You have to be careful with LI_ION batteries they can vent and burn if over charged. That's very unlikely charging with a solar panel. I originally set the maximum charge voltage to 4 volts to prevent over charging but found I did not get a full nights charge in the battery so I've changed R2 to 330 ohm and R1 to 100+680 ohm (total 780 ohm) to set the maximum charge voltage to 4.2 volts. You can choose your own resistors values and go to a maximum of 4.2 volts. Anything above that is likely to damage the battery. As a precaution it's probably a good idea to keep this type of solar lamp away from your house and anything flammable. Ideally you would want your LI-ION solar lamp to fully discharge over night or at least every few days. If it's not then maybe you might want to move your lamp to a partially shaded location. You can always add more LEDS if you think you have enough charge to power them.

The repaired garden lamps where I have added two extra batteries use the same circuit as the LI-ION lamp. You just need to change the LM317T resistors to set the maximum charge voltage to 4.8 volts and change the LED resistors to get 3 volts on the LEDS. On the web you can find several web sites that allow you to calculate the resistor values for a LM317T.

If you use the existing circuitry in your repaired garden lamps then use a LM317T to limit the maximum charge voltage to 1.6 volts for a single battery lamp or 3.2 volts for a two battery lamp. Connecting a 6 volt solar panel directly to a low voltage circuit will blow the chip on it. You can buy lower voltage solar panels but they cost the same as a larger 6 volt panel and I prefer to have a bigger panel for more charge.

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