Waitung for the capacitor to be charged?

[KungPhoo]

Hi. I'm not an electronic expert, and currently power an ESP32-CAM with a solar charged battery. I use a TP4056 for the charging I use a TP4056. My solar panel has peaks of 8V.
I wanted to use a supercapacitor instead now. So, the solar cell should charge the capacitor until I have enough energy to send an image to a server.
The ESP32 takes ~ 250mA and I need some 10 seconds to take a picture and send it. So 3.3V250e-3A10/3600h=23mWh.
When the capacitors are charged this much, I want the ESP to power on and send the picture - no matter if it's 5 minutes or 30 hours from the last sending. The problem is, the ESP draws like 10uA in "deep sleep" mode. This is quite something. I fear the capacitor will never charge if this load is always attached.
Also, I fear, that the ESP will be powered, when the capacitor is not fully charged, yet. So the sending will abort after like 3 seconds.

Is there any way to archive this?

[aresta]

Hello,
I think that it should work with your low requeriments, but your second concern is the most important. You have to make sure that the ESP32 only tries to connect and send the image when the supercap is over 50% or 40% or 60% or whatever that works.
Otherwise, if the ESP32 is starting to take power when the supercap is low, it will start to ripple on/off.

Regarding comsuption in sleepmode it should be less. If you use a devboard remove the led and the LDO (it has some quiescent current always event if you don't use it), and power the chip directly to the 3.3V VIN pin.
And make sure to wake up from deep sleep with wifi deactivated. Activate it only after checking that the supercap has enough charge. Don't use DNS but static IP, etc.

And you can use one of the new ESP32 with only one core are less power consumption.

But I think it should work. I was not able to connect to the wifi every 10 minuts, but your requeriments are lower.

[KungPhoo]

So, can you tell me how to only power the esp32, when 60℅ charge is reached? Because once the voltage gets too low, the chip is in a zombie state and will not recover, even if the voltage is enough, again. I think I need a mosfet or something.

[aresta]

You can use a voltage supervisor, it would only enable the chip when the cap voltage is above a minimum, with some hysteresis to avoid the ripple.

To avoid the ripple you can also try with several big normal decoupling caps close to the power pins of the ESP32, because the supercap has some 'bouncing'. It goes down about 200mV or more when the chip starts up, only for a short time, because of internal resistance and some 'chemical' effects. To reduce these peaks and the posible ripple and brown out, place several big decoupling caps in parallel (less ESR) and measure with the oscilloscope if it improves. But it will not solve completely the problem.

But you can also try to prevent to arrive to that situation. For example, before going to sleep check the voltage and if it is low program a longer sleep time, several hours. Make sure that it wakes up with wifi deactivated and sleep back inmediatly if the voltage is low, it sucks a lot of power on normal wake up with wifi, put more supercaps, etc.

With some sun the cap will charge very fast, in a couple of minutes. And it should survive one night without problems. You could also keep the aprox hour and sleep all night in a row. Or use a light sensor.