ESP8266 Community Forum

- Mon Feb 08, 2016 6:00 am #40675

Hi.

I've seen several suggestions here and on another blog where people have put a HT7333-A LDO voltage regulator between a 18650 and the ESP-01 board. Isn't an 18650 going to have too low a voltage output to be above the voltage dropout for an HT7333?

Can I echo torntrousers sentiment in asking for an example diagram of using an 81650, LDO regulator and ESP8266

Thanks

The standard Li-ion 81650 battery could be 'floated' at just under 4V so the above diagram could be used with a resistor change to set the LM317 output to 4.2V (i.e. make R2 560 Ohms) Then the battery will be charged to around 3.9V

Then between the battery and ESP8266 all you need to add is a fixed drop of 0.6V which can be a silicon diode e.g 1N4001
The LM317 is already providing a constant voltage, albeit 0.6V higher than required so the fixed forward voltage drop of the silicon diode does the job just fine. In discharge, the battery will fall to 3.6V and still be OK, the ESP8266 will drop to 3V and still be OK.

The good news is that if leads are kept short and sensible, the source impedance of this circuit is very low and that's something the ESP8266 "cares about" more than the actual value of Vdd.

Remember, my suggestion here has the goal of being a minimal solution - where a throw-away design is sought after. It is not as precise as a fully engineered design might be but I believe it to be perfectly adequate for its purpose.

- Tue Feb 16, 2016 9:39 am #41220 I have been trying to do about the same thing, but to keep it cheap, I bought a "Dizaul 5000mAh battery bank with solar charger" and a adafruit LM3671 breakout. The Lipo gets up over 4V, so you need to drop the voltage and the LM3617 is pretty efficient. I removed the battery from the power bank (don't use anything sharp to open it, Lipos puncture easily as I found) so it isn't sitting out in the sun and just extended the wires to use the charging circuit in the powerbank. No need to buy a new on if I don't have to. Connected the LM3671 to the battery and ESP and it works so far. The Solar panel is tiny, but once I start using deep sleep (hopefully this weekend) it should be fine to keep the battery topped up and keep the ESP powered for long enough to get through a cloudy week. I get 60 hours out of the 5000 mAh battery running contentiously, I should be able to get much more waking up every 10 minutes or so.

I probably took the battery down too far, but the LM3617 has an enable pin so it is possible to have it shut down when it gets below a set voltage. Battery bank and LM3671 cost me 19 euro, but if it works I can probably improve on that. I don't know if I can do better buying a battery, charging circuit and solar cell separately. The nice Adafruit solar Lipo charging circuit alone is 17.50 from adafruit. I will have to see how reliable it is, doesn't matter how cheap it is, if it is not reliable it is not worth it.

I would prefer using Nimh AA batteries, and I will probably set up one with 4Nimh AA batteries, 6V ish solar cell and LM6317 to see how well it works over the summer.