Probably your charge current was set low and your bigger panels had lot of margin.
I did little bit testing today with my 8W (verified) poly panel.
It has nominal voltage 6Vmpp, Impp 1.33A and 7.2Voc, Isc 1.6A (standard test conditions).
At actual conditions (autumn here, 1PM) I measured Voc = 7.1V. Isc = 1.05A. With variable load I found max output of 5.5W, Vmpp 5.8V and Impp 0.96A. That’s 65% of nominal and quite expected for actual conditions.
I then tested it with load higher than 5.5W to see output voltage/power collapse. Already +20% load made ~1V voltage drop and 12% less power output. Even higher load made voltage to collapse down to 4V. And that was measured on the back of the panel, the stock wiring caused additional 0.4V voltage drop to 3.6V.
My panel is 6V, but with 5V panel 20% “over-draw” would already drop voltage below TP4056 minimum voltage, it needs ~4.5V to charge at 4.2V.
So if you have plain 5V 3W panel with short wiring, max charge current at standard conditions would be 3W/4,2V=0.7A (without considering conversion losses) and in practical conditions around year maybe half of it. Even cheap pseudo-mppt solar charger would shine here.
Above is valid for normal panel, not for one with USB output. Circuit inside those remains unclear.
I use this solar controller with this panel and a 2000mAh battery driving an ESP32, a Dallas temp probe and a float sensor.
I use deep sleep and wake the ESP to update numbers ever hour. This sequence occurs during daylight hours only. At night, it sleeps through. I’ve never seen the overall battery SoC drop below 50% even in the winter months when the panel experiences a decent amount of shade and cloudy / rainy weather ( I live in South Africa ).
Nice board, especially for 3.3V output, so no need to step up and down.
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Skyman I have one of those little solar panels for IP cameras. It definitely is not 10W, and I would question whether 2W is theoretical or real-world.
FYI, I am using it with a 6600mAh LiPo and ESP32-s3 in my greenhouse which wakes 3 minutes every 30 minutes. On a few occasions I had to take a powerbank out to top up the battery in wet weather. FYI this is the last 7 days (in spring, partly cloudy most days) of solar panel current from the solar panel going into the DFRobot Solar Power Manager board.
Note however that these measurements are taken in the 3 minutes which the ESP32 is awake. A better gauge is the graph of battery voltage.
Tom_I’s list of questions indicate how many variables are involved - but most are hard to quantify. I started by using a battery I already had, bought a cheap solar panel, and gave it a try, and spent a lot of time experimenting to find what works for me.
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