Review on SMAKN Lithium Battery Charging Charger by Dee Rawls

I have replaced my 10 year old Oregon Scientific rain gauge with a new La Crosse 724-1710 Wireless Rain Gauge Weather Station after years of good but declining performance. For my yard, the top of the vent in the middle of the roof of my home provides the best possible location for a rain gauge, clear of rain screen structures, yard trees, etc. However, a major downside to this location is the scaling roof, replacing rain gauge batteries on a regular basis. Unlike Oregon Scientific's device, which was constantly charged by a small solar panel, La Crosse's device uses two AA batteries that need to be replaced regularly. So my engineering project was to replace the two AA batteries in La Crosse with a small solar powered battery. deliver. The two AA batteries in the La Crosse device are said to last about a year, so the power consumption is quite modest: 3 volts and about 1600 mAh total power consumption for a year. Fascinated by the capabilities of the new Li-Ion batteries, I have decided to replace the two AA batteries in the La Crosse unit with a Model 14500 Li-Ion battery with a stated capacity of 1650mAh. This 14500 battery is the same size as a regular 1.5 volt AA battery but produces a higher voltage of 3.7 volts. Only one 14500 battery is required to get the 3.0 volts needed by the La Crosse unit along with the addition of a series diode to bring the voltage down 0.7 volts from 3.7 (battery voltage) to that of the rain sensor required 3.0 volts to lower. My goal was to use a small 5V solar panel to continuously charge a 14500 battery and thus avoid having to scale the roof to service the rain sensor. So the engineering challenge was to connect the small solar panel to the 14500 battery in a way that efficiently uses the power generated by the small panel and prevents overcharging of the 14500 lithium-ion battery such as nickel-cadmium and nickel-metal hydride , are very sensitive to overcharging and do not tolerate continuous charging. This has led to the emergence of dedicated charge controllers on integrated circuits like the TP4056, specifically designed for use in charging lithium-ion batteries. These charge controllers typically charge at a fixed current until the maximum charge voltage of 4.2V is reached, then quickly cut off all charge current to prevent overcharging. Miniature circuit boards, such as the one featured in this review with the TP4056 and its ancillary components, are readily available for connection to standard 5V USB cell phone power supplies, one wonders if they could easily be connected to a 5V Solar panel can be used to charge a lithium-ion battery? Short answer: yes. Unlike a 5 volt USB power adapter, which delivers a high current at a fixed 5.0 volts, a solar panel delivers a very variable but limited current (proportional to sunlight) with a current-to-voltage ratio determined by its IV curve is determined. In order to use the solar panel's output power efficiently, the applied load must operate near the panel's maximum power point (MP) on its IV curve, which is a point near the knee of the IV curve. Fortunately, a fairly useful means of reaching the maximum operating point of the power array is to use a constant voltage load (such as that provided by the battery charger), where the constant voltage is moderately well matched to the array's maximum supply voltage. A constant voltage load works well because the maximum power point voltage is not very dependent on the light level. Now back to our TP4056 IC and how well it couples to the solar panel. Answer: very well. The current limit feature of the TP4056 is virtually inactive when used with a solar panel as the solar panel itself limits the input current (unless a very high current array is used). The TP4056 draws power from the solar panel at a fixed voltage of around 4.3 volts and stops charging the battery when the Li-Ion battery voltage reaches 4.2 volts. Exactly what he should do. It also prevents reverse current from the battery to the solar panel when not charging, eliminating the need for a blocking diode. The only design challenge is to buy a solar panel with a maximum supply voltage of about 4.3 volts. The input voltage is set by TP4056. It turns out that this is well supported by the many small 5-6 volt solar panels available from Revain. MY FINAL DESIGN The attached drawings illustrate my final design using a very small (1" x 2") 5V 30mA solar panel connected directly. to my 14500 Li-ion battery via a small TP4056 charge controller board. No additional components were required other than a series diode (e.g. 1N4001) used to drop the battery voltage from 3.7 volts to 3.0 volts to accommodate the 3.0 volt input voltage required by the rain sensor. All components (battery and TP4056 board) fit easily into the rain gauge battery compartment and a tiny solar panel has been installed alongside a good view of the sun. have about 2800 peak hours of sunshine per year. Multiplying that time by my 30mA charge current, I get about 84,000mA-hours of battery charge per year, which is far more than a rain sensor needs. Nice compact but very conservative design. And no more climbing on the roof.