I'm working on a project that will eventually be a solar pool thermometer using super capacitors for short periods when needed.
For now to keep things as simple as possible I am using the blink sketch to blink the on board LED.
The sketch works when powered by the USB or when powered with 3.3 volts from the bench power supply.
It does not work when powered by solar cell unless I press the reset button. Then it works perfectly.
I checked the voltage going into the Lolin32 and it slowly climbs up to 3.3v, taking around 8 minutes.
I suspect its because the voltage climbs so slowly.
I need to use super capacitors because the project will eventually be in all day, direct sun floating in a pool- I'm figuring the temps wil be over what a LiPo can handle.
Any ideas on how to make this work?
I'm using these parts:
Solar cell 7 volt 2.38 watt
Schottky diode
3, 10F 2.7 volt super capacitors
Lolin32 board link
Voltage regulator link
Schematic img20240506_20191956.pdf (74.0 KB)
To limit possible sources of issues I'm using a blink sketch.
```cpp
#define LED5 5
// the setup function runs once when you press reset or power the board
void setup() {
// initialize digital pin LED_BUILTIN as an output.
pinMode(LED5, OUTPUT);
}
// the loop function runs over and over again forever
void loop() {
digitalWrite(LED5, LOW);
delay(500); // wait
digitalWrite(LED5, HIGH);
delay(500); // wait
}
The reset controller can keep the MCU in the reset state until the voltage is high enough for operation, or keep the system power shut down until same, possibly using a Pololu Power Switch.
By using deep sleep states, you do not need monstrous capacitors for such a simple task. Take a look at Nick Gammon's super-cap solar powered Arduino project.
In place of the parts list post an annotated schematic showing exactly how you have wired this. It is a hardware problem use the language of electronics schematics it will get you a better answer faster.
Thanks for posting the schematic, that shows you have not wired it properly. The super caps should be placed between Plus and Minus input of the converter. Placing them in series will not work as there will not be any current flow. I am not sure why the diode, it may not be needed.
AND! The capacitors must be in parallel and the must be charged through a current limiting resistor. When capacitors are discharged they are a "short circuit" when placed across the power source and will rely on the resistance of the solar cell to limit the current.
Depends on there voltage rating. I assumed since the OP placed them in series that was the reason why. Also a small solar panel should have enough resistance not to damage things.
By shorting a solar panel you won't harm it . Solar panels are designed to work almost at their maximum current all the time. A simple way to check a solar panel is to connect it to an ammeter in a short circuit. If a solar panel gets damaged in this test, it's probably faulty.
And exceeding the voltage rating for an instant will be the end of those capacitors, as I understand them. I have some surplus super caps and probably should try to destroy them!
Thank you everyone for the responses. Lots of great information.
I've ordered the parts for the charging circuit and will post an update when they arrive.
Thanks again.
