ESP8266 Community Forum

- Wed Feb 03, 2016 5:54 am #40343

I'll just chip in with another suggestion here if I may. LiFePO4 cells are much more tolerant and have several characteristics that make them more suitable. ... All that's required is a constant voltage regulator. And a blocking diode.

Could you draw a diagram of what you mean - would the voltage regulator be between the solar cell and LiFePO4, and the ESP directly connected to the LiFePO4 ? And wouldn't it still need some over discharge protection?

- Thu Feb 04, 2016 5:16 am #40396

Hi Jim,

I agree with your sentiments re ideally paying no more than a couple of $ for the charger, and i've been meaning to try this so you spurred me on to give it a go. Here it is:

solar1.jpg

Thats one of those 43cent charger modules you linked to, with a 5.5V 0.66W 120mA Solar Panel, a 240mAh LIPO cell, a MAX604 voltage regulator and an ESP-12 with a BME280 sensor. The ESP is publishing the temp/pressure/humidity to Thingspeak once a minute to here, and deepSleep'ing for the rest of the time.

The 240mAh cell is way to small for serious use. Its presently charged up to 4.0v and by my calculations it might last for about 60 hours if there was no charge from the solar cell, so a couple of cloudy days and its toast.

Come back here on Thursday to see how its doing, i'll try to put it somewhere sunny...

Ok so 60 hours later and checking the battery voltage with a multimeter this morning its almost right on 4.0v. The ESP hasn't missed a beat and published to Thinkspeak every minute. I had also checked over the last days, the day before yesterday it was quite sunny and the voltage got to 4.2v by lunchtime so i guess the charger would have switched off and the afternoon sun got wasted, then yesterday quite cloudy so didn't charge much.

So all in all that setup seems to work and be self sustaining. Will put in in a box and leave it in the garden to see if it keeps going forever...

- Sun Feb 07, 2016 4:10 pm #40645 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

- Mon Feb 08, 2016 5:41 am #40673

I'll just chip in with another suggestion here if I may. LiFePO4 cells are much more tolerant and have several characteristics that make them more suitable. ... All that's required is a constant voltage regulator. And a blocking diode.

Could you draw a diagram of what you mean - would the voltage regulator be between the solar cell and LiFePO4, and the ESP directly connected to the LiFePO4 ? And wouldn't it still need some over discharge protection?

Sure, this is what I was describing:

PVESP.png

The battery does need undervoltage protection but this can be provided by the software i.e. reading Vdd periodically and going into deeper sleep. The optimum details for that would have to be thrashed out but worth the effort in order to eliminate additional hardware.

Edit: R1 R2 could be replaced by a 1K preset potentiometer which would allow adjustment of the output. This removes the need for slightly harder to get E24 resistor values. A well-calibrated meter would have to be used to check for the voltages shown before the battery was connected.

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Last edited by AdrianM on Mon Feb 08, 2016 6:50 am, edited 1 time in total.