- Sat Oct 31, 2020 7:59 pm
The unit is officially able to run down to 2.5V, and I have tried running permanently on 2.8V and find it to be stable. I currently use a buck/boost converter and it works really well - they do the regulation so you don't need another LDO.
I've done a lot of mucking around with power circuits and found some really interesting things:
- an LDO is great for regulating a unit that's powered from a supply as they are very cheap, but is a disaster for battery. The excess voltage is dissipated as heat and it essentially acts as a big resistor, so the higher the voltage difference the higher the current it draws while working. The end result is that your batteries drain super fast until you get close to the LDO voltage. My first battery powered box used 3 D cells in series and a 3.3V LDO, and I chewed through the power in days. Really disappointing.
- the buck/boost converter was so much better. In buck mode it gave me 3.3V and used the excess voltage to make up current so the current draw in steady state on mode was only about 20mA for the whole module.
- in boost mode, however, the boost circuit made up the voltage by using more current, which meant that as the batteries drained the circuit pulled more current, which pulled the battery voltage even lower, which pulled even more current, which... so the effect was to drain the batteries very quickly at the end of their life. So for a more complex and expensive circuit, I really only got a few more hours of power
- the LDO circuit did have one good result. It showed (like you have found) that the ESP kept running way lower than the 3.3V that I thought was needed. My sensors stopped working before the ESP did. This led me to change everything to lower voltage and I found versions of my sensors that ran at 2.8V and 1.8V
I am now in the process of changing to a 2.8V buck only converter and an LDO for the 1.8V sensor circuit because the current draw is tiny. This will let me run nicely on batteries right down to the cut off voltage for rechargables, directly off solar, or off dry dells as well.