DIY WATERPROOF SOLAR POWERED SmartThings Contact Sensor - Outdoor Z-wave Zigbee Door Smarthome
In a previous video, I showed how to make a waterproof SmartThings compatible sensor for outdoor use. What I've discovered using it is that the battery depletes faster when used outdoors due to more rapid temperature changes which cause it to report the temperature more often and consume the battery faster. Also, the battery depletes faster in winter when it is cold.
The solution is to add a small solar panel to recharge a lithium rechargeable 2450 coin cell battery using an inexpensive charging circuit.
Rechargeable 2450 Coin Cell Battery
The stock battery in the SmartThings Multipurpose sensor is a 3V CR2450 battery, which has a capacity of 600-620
There does exist a 3V lithium coin rechargeable battery known as the ML2430, which is 3mm thick instead of 5mm thick like the CR2450. I have not been able to find an ML2450 3V cell.
The most common 2450 rechargeable battery is the LiR2450 which typically has a voltage of 3.6-3.7V, and a capacity of 100-125 mAh and can be recharged 500-800 times. This size coin cell battery is popular for use in CMOS memory for computer motherboards. When you purchase, please make sure to buy the one without tabs.
Where To Buy LiR2450 Battery
LIR2450 batteries can also be purchased with a charger, like this set I purchased so that I could start using the batteries immediately while I work on the solar charging circuit.
Lithium Coin Cell Charging Circuit
To properly charge the lithium coin cell battery, a lithium charging circuit is required. I found a small one designed for coin cells (LINK). It has a 4.2V output (for 3.6V cell), and 50mA charging current.
The following images are from the eBay listing for the charging circuit
If the above charger is not available to purchase, you can also use a inexpensive Micro USB 5V 1A Lithium Battery Charging Board/ Charger Module
Although the charger has a micro USB connection, it also has some PCB solder points for power in. The link above has instructions on how to replace the resistor with the correct resistor to reduce the charge current to 50mA.
The solar panel needs to provide a minimum of 5V of power to be able to charge the battery using the lithium charging circuit.
If the waterproof enclosure box is exposed to sunlight (as is in my case), the easiest mounting solution is to mount the solar panel on the box, so ideally the solar panel is small enough to fit on the side of a box.
These 5V 60mA solar panels are small enough to attach to the sides of the box.
The products shown here were purchased by me with the intent to use them. I did not receive any free items, and I am not being paid or compensated for this review. The video and description may contain affiliate links. If you click on a link, I may receive a commission. Money earned helps to support my channel and bring you more informative videos about engineering, crafting, and DIY.