I’ve got a build of the wireless weather station from https://learn.sparkfun.com/tutorials/we … nderground setup and I’m running into power issues. It’s been running fine for a few months until this last week when it stopped getting enough of a charge during the day to run overnight. I’ve tried changing the reporting interval to reduce load, but it hasn’t had enough of an impact yet. My current thinking is the recent weather has impacted charging (overcast and rainy), but the battery pack is supposed to be sized correctly to run the system for ~5 days.
When I built my version of the station, I had to substitute a different charger and battery for the sunny buddy. The change in charger required me to add a step up/down regulator. I’m guessing that’s causing a drastic difference in runtime, but I’m having a hard time calculating the impact.
My deviations from the SparkFun parts list are below:
As each part has it’s own efficiency loss (or non-ideal power conversion) that likely means in the end less juice got into the battery. A regular stepdown/up regulator doesn’t care about the panel voltage and current on it’s input. It only cares if itself is outputting 5 volt. That means the solar panel is probably operating at less efficient power point, meaning you’ll get less watts out of it. And the battery charger is another additional source of loss. The MPPT tries to draw just enough current out of the panel such that the panel voltage doesn’t go to either extreme (up or down) and that means the power coming out is optimum. Check the Sunny Buddy hookup guide to see what it this power-point is all about.
Measure the current and voltage coming out of each stage (solar panel, step-up/down regulator, battery charger). You’ll need multiple multimeters (stages x 2) for that to get some hard data on what you are loosing. And I DO mean you should measure both voltage AND current to get power. Only voltage doesn’t say anything.
The Adafruit charger has a very serious weakness and is not protected against input voltages higher than the 7V absolute maximum for the controller chip. Since your solar panel can easily exceed that voltage, it may have damaged or destroyed the charger.
Adafruit engineers are aware that this is a bad design, but instead of offering an explanation, a warning is prominently displayed on the product page that the charger is intended only for “5-6 V” panels they sell. This is very bad public relations policy!
Please purchase this kit and panels from Adafruit to ensure optimized functionality!
Thanks all for the feedback. I should add that I noticed the warning on the charger page and made sure to use a panel from Adafruit (6V 2.5W Panel - https://www.adafruit.com/products/200). I believe this will produce no more than 7V and thus not damage the charger. When I check the enclosure outside the charger LEDs seem to indicate it’s still operating.
One of the reasons I didn’t use the sparkfun sunny buddy was due to lack of support for a temperature probe. Nate mentions on the weather station build page he hasn’t had any issues with the battery so far, but I’m wondering if the lack of a temp prob impacts battery life.
It is indeed. I ran an extension cord out to the enclosure last night to let it charge fully overnight. It ran a full charge cycle and after I removed it this morning has been running ok. So the charger isn’t the problem. I’m leaning towards the charger + regulator being the issue, but as suggested checking with a DMM seems like a good next step.
Interestingly, my data from the charge cycle last night indicates a worst case current draw of ~17 mA from the wall charger (Wifi active every 5 minutes).
To provide some closure to this thread many months after the fact, I replaced the charger I was using with a sunny buddy and dumped the regulator. That solved my issue. Long story short, the regulator was causing the problem. Thanks for all the help!