Im making a small project where my module collects some data from the environment and sends it to the database. Since my module will be placed on the area that's not easily accessed I need external power supply. I was thinking about a 5V 3000mAh battery (found some lithium polymer rechargeable ones on the ebay for ~20$) but since the module collects the data every 10-15 seconds it needs to be on all the time and at that rate I calculated my battery would drain in few weeks time. So I came to an idea to use small solar panel that would charge the battery during the day and that way I don't need to replace it every other week. The problem with this is how do I protect the battery from overcharging? I looked and found that there are some BMS but really not sure on how they work and which one could be good for my system. Did anyone do a similar way of power supply and if so what are your experiences with BMS and battery charging.
tuadru:
I was thinking about a 5V 3000mAh battery (found some lithium polymer rechargeable ones on the ebay for ~20$)
You need to post a link to the technical specs for that particular battery. 5v is not the natural battery voltage. LiPo cells produce 3.7v so your system is likely a 7.4v battery with some electronics to reduce the voltage to 5v.
If you can run your project directly from a single LiPo cell (3.7v to 4.2v) you will avoid the energy losses in the voltage reducer.
You can get microchips that operate as complete LiPo charge controller - for example the Microchip MCP73831/2. Note, however that that device is designed for a max input voltage of 6v so you may need another voltage regulator between it and your solar cell.
...R
Not sure if I can post link from the aliexpress of the battery Im planning on ordering so here are its specs as shown on the site:
Brand Name:
BJNPOWERWIN
Type:
Li-polymer
Replacement Battery:
No
Set Type:
Batteries Only
Model Number:
5v 3ah
Size:
about 12.5 mm * 38 mm * 62 mm
Nominal Capacity:
3000mAh
Does the AliExpress website explain how to charge the battery?
...R
PS ... I can't think of any reason why you can't post a link to the AliExpress website
tuadru:
Im making a small project where my module collects some data from the environment and sends it to the database. ...since the module collects the data every 10-15 seconds it needs to be on all the time
Doesn't have to be "on" all the time. You can put the MCU into sleep mode for the 10-15 seconds, wake it up, do the measurements, and have it go back to sleep.
Power Saving by Nick Gammon
TUTORIAL:A GUIDE TO PUTTING YOUR ARDUINO TO SLEEP
Don't know which MCU you're using, but here's one for a Pro Mini
I was unsure about forum rules Robin2.
Here is aliexprees link:
surveyranger as my module will be connecting to wi-fi network it doesent make sanse to make it connect every 15 seconds.
That battery seems to have a separate connection for charging and there is a package offer of battery and charger which (with my schoolboy French) seems to say that the charger is designed for charging a LiPo battery. Without more information about the internal connections within the battery pack I would be reluctant to charge the battery without using that charger. LiPo cells can explode or go on fire if they are abused.
...R
tuadru:
survey ranger as my module will be connecting to wi-fi network it doesent make sanse to make it connect every 15 seconds.
The only thing that doesn’t make sense to me is why your thinking it makes sanse to try to maintain a 24/7 WiFi connection when you in fact just need 1/15 of that connection time and power use.
tuadru:
surveyranger as my module will be connecting to wi-fi network it doesent make sanse to make it connect every 15 seconds.
As I said earlier, I don't know what you're using because you didn't describe your setup or provide a schematic. I can't speak for every single module with a MCU, but there is most likely a sleep mode (AVR chips have them and ESP8266 modules have them). The mAH not used during the 10-15 seconds of sleep will add up over the day, and it'll decrease charge/discharge cycles of the battery.
It doesent make sense cause it takes approximately 12 seconds for the module to connect to the wi-fi network and send the data to the server which is close to 15 seconds, so the power save would just be those 3 seconds. Anyway even if I do all that the problem still stands, the battery would just prolong its life from 15 to lets say 20 days before it drains. I still need to charge it somehow and it doesent make any difference in my initial problem which is finding correct solar panel and rechargeable battery to go with it.
tuadru:
It doesent make sense cause it takes approximately 12 seconds for the module to connect to the wi-fi network and send the data to the server which is close to 15 seconds, so the power save would just be those 3 seconds.
If battery life is an important issue why not store several successive items of data on the Arduino and only send them to the internet once every 5 minutes.
...R
Robin2:
If battery life is an important issue why not store several successive items of data on the Arduino and only send them to the internet once every 5 minutes....R
I see what you are trying to get to, but from my understanding what tuadru's trying to do is not extend the time between charges, instead of that he's trying to get rid of charging the system completely using a solar panel that constantly charges the Li-Po battery. Other than that I really have no answer as I've never used a solar charger, but if we could somehow see how much we have in the battery and put a deadband between fully charged and "usable" battery states, we might be able to use a relay to control the flow of current from solar panel to Li-Po. Deadband is there for just to keep relay off for a while, otherwise it'd just go on and off all the time.
Okay Robin , so if not that battery do you have any other suggestion for a battery I could use to charge with solar panel, as I try to keep my project low cost I was thinking about doing it with this solar panel from the link below:
P.S.
I understand that all would help because it would reduce the need to charge the battery too many times and prolong its life which is all good and plausible, but the main problem still stands and that's I still need solar panel to charge the battery and I still need overcharge protection no matter if its charging 5 times a day or 1 time in 5 days. I need to somehow monitor the battery status and with that enable or disable charging of that battery via solar panel.
How about a 5V solar power power bank (the kind that charges phones & other electronics)? They have the solar cell, battery, and control modules already built in. Some are even waterproof. They are also readily available at Wal-Mart, Best Buy, Harbor Freight, and others.
Great idea surveyanger Ive just checked some on aliexpress. Not that expensive either. Is it correct they can have capacity up to 30000 mAh? That would be great especially since I can plug the power directly via USB port to my module. I need only now to find specs of the solar panel on those modules to see if they will charge the battery faster than it drains and how will it last for my project. Thanks man you might just be a life saver 
tuadru:
Okay Robin , so if not that battery do you have any other suggestion for a battery I could use to charge with solar panel, as I try to keep my project low cost I was thinking about doing it with this solar panel from the link below:
I am not familiar with the things that @surveyranger has suggested in Reply #13, but it sounds like a convenient solution - especially if you have no electronics experience. HOWEVER you must make sure that the solar panel can produce more than enough energy for your project. If not the batteries will eventually run flat.
I don't have a suggestion of my own because I would approach the problem differently -
either using a single LiPo cell (3.7v) directly with a suitable LiPo charger
OR,
using a 6v or 12v lead acid battery. Lead acid batteries can take a lot of abuse and if the battery has a sufficient capacity it could probably be directly coupled to a small solar cell directly. However lead-acid batteries do not like to be left in a discharged state for a long time - they should get a really good charge about once a week. Of course if the solar panel can easily meet the needs of the Arduino etc that won't be a problem.
The Battery University website has a great deal of useful info about all the different battery types and the appropriate precautions.
...R
tuadru:
Great idea surveyanger Ive just checked some on aliexpress. Not that expensive either. Is it correct they can have capacity up to 30000 mAh? That would be great especially since I can plug the power directly via USB port to my module. I need only now to find specs of the solar panel on those modules to see if they will charge the battery faster than it drains and how will it last for my project. Thanks man you might just be a life saver
No problem. I looked at a few of them, and they said to charge it with a wall charger first. I guess the solar panel is more for trickle charging. The more Watts (W) a solar panel has, the faster it will charge the internal battery (regardless of battery size).
2W/5V = 400mA - efficiency losses
5W/5V = 1A - efficiency losses
10W/5V = 2A - efficiency losses
....and so on