ESP32 and solar cells

[froussel]

As my ESP32 are of the kind scattered in the nature and accessible physically (also for a physical reset approximately every 6 months) they are powered by photovoltaic.

Cells -> charger TP4056 -> 18650 -> 1S 3.7V 3A Li-Ion BMS PCM battery protection board 18650 lithium battery -> ESP32 (without booster which consumes too much continuously and can not be put to sleep and the ESP works well in the battery voltage zone corresponding to a battery not discharged).


Most of the time ESP is in deep sleep and the program if it encounters an action that can not be completed puts the ESP back into deep sleep.

When there is sun the battery recharges.
When the battery is full the charge is stopped.
When the battery is empty the bms stops the power supply of the ESP to avoid the destruction of the battery in deep discharge.
If the sun keeps a charged charge of a little at depth all is well.

If the lack of sun causes the BMS to cut due to flat battery, as soon as the sun recharges the battery the BMS feeds the ESP but it does not have sufficient intensity (well it is this which I imagine)
 It has a bad initialization and the program is not launched but the ESP consumes permanently and can not get back to sleep and the cells are unable to provide only what to start properly or I would have a cell pack really oversized.

Questions :
- the pin reset of the ESP to the ground resets the ESP32, if it is maintained to the ground the ESP32 does not start but consumes it power ? (in the sense too much to prevent the charging of the battery with a weak sky)
- If this is the case how to maintain the pin reset to ground as long as the battery is not at a certain voltage (defined by the one it has when it is loaded for example to 30%).
- How to prevent the ESP from starting if there is not yet a sufficiently charged battery?
- Are there specialized circuits that themselves consume almost nothing to put it before the BMS or after and then are they satisfied with the very low intensity available?

[bobtidey]

Most ESP32 modules have the EN / Reset pin internally pulled high through a 10K resistor. So grounding this pin will draw a significant current (330uA) despite the ESP32 being off. The ESP8266 is slightly superior in this respect as it has separate EN and RST pins and the EN does not have an internal pull up, so a high value (e.g. 1M) can be used to minimise current.

One approach would be to use a reset controller like a LP3470 and use its reset to control a MOSFET switch in the power chain to the ESP32 module. E.g. battery voltage < 3.6V, LP3470 reset goes low, turns n-channel MOSFET off. Drain of the MOSFET becomes the 0V feed to the rest of the circuit. The LP3470 has a small quiescent current and has a bit of hysteresis between turning off and back on again, and a delay may also be added during the turning on part.

[froussel]

Thanks
A small diagram would be a great help... I'm not electronics

[bobtidey]

I think something like this would work.

LP3470Reset.jpg (10.49 KiB) Viewed 11296 times

Battery includes any charging / protection circuit you are using.

When voltage is above 3.6V RST is high, MOSFET turns on and connects circuit ground back to battery ground.

Capacitor controls delay on releasing RST after battery goes above 3.6V. 1uF is 2 seconds. Use larger if longer delay wanted.

[froussel]

Thanks !

[Mike1997]

...or use this solution here: viewtopic.php?f=17&t=11270