Sunny Buddy not keeping battery charged

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Sunny Buddy not keeping battery charged

Post by brooksdr » Sun Jul 16, 2017 9:24 am

I have a breadboard setup with a Pro Mini collecting data from BME280 T/RH/press DHT22 T/RH sensors. A real time clock board and micro SD card board are used for recording data. My code collects data about every 2 minutes with Narcoleptic delays inserted between data collection and recording events. This circuit draws about 25 mA during data collection/recording and about 10 mA when the Narcoleptic delay is in effect (most of the time).
Powering this setup with a 6-V 3.5-W sparkfun solar panel, a Sunny Buddy, a 4400 mAh LiPo battery, and a buck-up converter to provide 5V to power the Pro Mini seems like it should work continuously. However, I find that the battery does not stay charged and after a few days (even now, during the height of the summer), the system shuts down. Yes, I have followed the instructions about setting the knee voltage to around 3V.)
Why won't this setup keep the battery charged?? Do I need a larger battery? A larger solar panel? (With a larger panel, or two panels in parallel, perhaps I could increase the charging current?)
Any suggestions will be greatly appreciated!

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Re: Sunny Buddy not keeping battery charged

Post by jremington » Sun Jul 16, 2017 6:34 pm

You should measure the current drawn from the battery and supplied by the charger to understand the reason for the failure to maintain charge.

However, your entire approach is really the wrong way to go. Get rid of the boost converter and the regulator and LEDs on the Pro Mini (swipe them off with a solder pencil) and have the sensors either sleep or arrange to have their power controlled by a separate transistor switch.

Follow this excellent tutorial on sleep modes closely, and you should be able to run the entire system off of 2 X AA batteries for months, or use the LiPo/solar charger if you like:

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