I am looking to build a wireless solar powered sensor that I am planning on mounting on a wooden structure. Since I live in a rather hot climate and fire hazard is a concern, Li-Ion and Li-Po batteries are out of my considerations.
I have been experimenting with ultra-capacitors, however found out that their self-discharge rate is so high that the capacitor would not last through the night after a cloudy day.
Alternatively, I've been thinking of a circuit based on NiMH batteries but have not found much information in this regards.
Power draw of my sensor will be under 10 mA, running from a ~3.3v source (actually I'll need both 3.3v and 5v but switching step-up regulator would cover the 5v).
I'd really appreciate if you guys could share your thoughts, experiences or ideas in this regards!
I am using a 20W solar cell, 186650 2600mAh battery, a ESP32 and a BME-680; yea I read, no Li battery, just relating experiences.
I originally used a 10 watt solar cell to find that as long as there were no clouds, wireless on, the solar cell was able to recharge the battery during the day. On days of less than ideal clear skies, the battery would not get a good recharge. A 20W solar cell recharges the battery rain or shine.
The most important aspects of power management is being able to put the ESP32 to sleep in between readings and the low power consumption of the BME-680 (all 3.3V devices). I leave the BME-680 with power during the ESP32 deep sleep.
I use a switching regulator to regulate the solar cell output down to 5 V. The 5V is sent to a MCP73871, the output of the MCP73871 is sent to a MCP1700, and onto the sensor and ESP32.
Wireless is the largest power consumer. I use a antenna on the ESP32.
The 'overnight' method looks like the easiest way for a solar charges, except it would be an "over day" method.
More and more I'm inclined towards using a 3 cell NiMH battery rated at 3.6 nominal voltage. It seems I will be able to use a CN3065 based solar charger without any issues as long as I don't go overkill on a solar panel.
Idahowalker:
I am using a 20W solar cell, 186650 26000mAh battery, a ESP32 and a BME-680
I must assume you have a typo in battery capacity, otherwise it sounds like you are powering a satellite transponder
Have you measured power draw of your device? Sounds like you have a very power hungry set up in there, but to be honest I have never done any battery operated esp based devices, so power consumption of an esp was never a concern for me.
My current project will be running off an atmega+NRF24 radio, and even before any power-down states the power draw of this combo is about 5 mA. In power-down mode that combo is down to 6 uA (as I have another sensor that works for about a year off a single CR3032), but with this project I will not be able to put atmega into pwrdwn mode as this will be timing critical device.
But there was no mention of size being an issue in your first post.
Yes, I did not mention that - but I do want to stay within reasonable proportions.
To me it is unreasonable to have a several pound battery hanging on a wall to power a 10mAh device In other scenarios I agree - lead-acid seems like a very reasonable alternative where space and weight is not a concern!
bocat:
I must assume you have a typo in battery capacity, otherwise it sounds like you are powering a satellite transponder
Have you measured power draw of your device? Sounds like you have a very power hungry set up in there, but to be honest I have never done any battery operated esp based devices, so power consumption of an esp was never a concern for me.
Oops! Yuppers a typo 2600mAh. I have hard the setup run for 4 days/4 nights on just battery; exceeded my requirements.
I use LiFePO4. They can run a 3V uC without a regulator. There are modules that can solar charge them (TI makes one). NiMH is more popular since they are more accessible and have a safe chemistry.
bocat:
Yes, I did not mention that - but I do want to stay within reasonable proportions.
For many applications a lead-acid battery has very reasonable proportions in both dimensions and weight. If you have a specific size/weight limit in mind, specify that with numbers, not with woolly wording. Don't forget to add the required capacity as well.
The #1 choice for larger solar installations is the lead/acid battery, of the deep cycle type. Cheap, reliable, safe. The main problem is the lead and acid pollution when the battery gets damaged and leaks its contents.
The #1 choice for smaller solar installations is LiPo. Costs a lot more per capacity, but much smaller, reliable and safe - get one from a reliable manufacturer, not a no-brand or unknown brand made-in-China one. There are billions of LiPo batteries out there nowadays (for starters every single mobile phone has one), and it's not that spontaneous combustion is a serious issue unless the battery gets damaged, or is otherwise abused (poor charging circuits).
wvmarle:
If you have a specific size/weight limit in mind, specify that with numbers, not with woolly wording. Don't forget to add the required capacity as well.
The #1 choice for larger solar installations is the lead/acid battery, of the deep cycle type. Cheap, reliable, safe. The main problem is the lead and acid pollution when the battery gets damaged and leaks its contents.
The #1 choice for smaller solar installations is LiPo. Costs a lot more per capacity, but much smaller, reliable and safe - get one from a reliable manufacturer, not a no-brand or unknown brand made-in-China one. There are billions of LiPo batteries out there nowadays (for starters every single mobile phone has one), and it's not that spontaneous combustion is a serious issue unless the battery gets damaged, or is otherwise abused (poor charging circuits).
I understand you are one of those that need to leave your footprint in every thread to keep your scores up, but your comment to my question brings zero value.
I don't disregard the suggestion of Srnet in any way or try to make fun of it. All I said it does not fit my project needs (although I did look into that approach) and here comes you, acting all smart a, who doesn't even dare to try to understand what I am asking for and my needs. I am not placing a purchase order for an engineering sample for a commercial satellite to be providing all the details and drawing. I'm asking for a fellow hobbyists' experiences on a hobbyist forum.
I made it clear that my device will be operating on a 3.3v source with power consumption of under 10mA - what part of this makes you wonder what capacity battery would I need if you are really that proficient in your advice? I also specifically stated - no Lithium based storage devices and yet here you are pushing your "#1s choices". - I get those are number 1 for certain uses as well as I understand pros and cons of each, but this is not what I am asking for.
Small lead acids don’t weigh much at all .it may be well worth your while looking at power saving measures, as previously mentioned ,too to get the battery size down. What are you sensing - could you put everything to sleep at night ?
hammy:
Small lead acids don’t weigh much at all .it may be well worth your while looking at power saving measures, as previously mentioned ,too to get the battery size down. What are you sensing - could you put everything to sleep at night ?
Thanks for the link! That's the smallest one I've seen so far! Interesting that searching on Amazon and Digikey I did not see anything comparable, but when searching with product code I've found a few that are just under 1 pound mark. I am thinking to try a 3 cell NiMH as a primary option for now and if that fails, the smallest lead-acid I can find will probably be my second choice.
I am planning on building a wireless Geiger counter that will be sending data through NRF24l01 to the main "hub" inside the house, potentially with some additional sensors such as BME280 to measure parameters inside of a completely sealed enclosure for control purposes. Currently I have both the geiger counter and CR2032 fed wireless sensors operating in separate devices, so can work down atmega+NRF+BME280 combo down to about 4uA power in sleep mode, however with catching clicking events from the Geiger counter, I am thinking to keep Atmega running in regular mode as pwrdown-wake routine is usually taking some time and can introduce inconsistencies in timing between events recording. Geiger counter consumption is under 1ma.
I could work out the whole circuit to operate with several AA batteries that would last at least half a year, but that would be a boring approach, thus I'm looking into a more interesting safe and sustainable power solution.
