Background: I have a project that will be in a remote & seldom monitored location, therefore I am choosing a LiPo battery with appropriate solar charging system to power the project.
The LiPo battery will be supplying power to an Arduino Pro Mini 328 - 3.3v/8Mhz board and a Sparkfun Qwiic MP3 Trigger (DEV-19030) board.
I envision the system as follows:
Lithium Ion Battery - 2Ah (PRT-13855) connected to the output of an appropriate single cell charger.
The appropriate charger will have a Solar Panel Charger - 10 W (PRT-16835) as its power input device and will be connected to the lithium battery at all times.
The battery will also be connected to the Pro Mini & MP3 Trigger boards at all times.
Can the charger device protect the battery from being completely discharged by the Pro Mini & MP3 Trigger boards if the solar panel cannot produce power due to no exposure to the sun for an extended period? Or will I have to connect some isolation/monitorng device between the battery and the 2 powered boards?
The 2 seemingly appropriate LiPo charges that I found are Sparkfun LiPo Charger Plus (PRT-15217) or the Sparkfun Battery Babysitter - LiPo Battery Manager (PRT-13777). Are there other Sparkfun chargers that I should be considering?
I would appreciate your direction/suggestion for the best charger and battery drain isolation device (if needed) given the following questions I have:
Q1. The system might be temporarily placed in a shaded area for a few days, I want to avoid completely discharging the battery given no solar generation during that period.
Q2. What should be the minimum and maximum charge rate for the LiPo 2Ah battery I indicated (PRT-13855)?
Q3. Have I selected the correct Solar Panel (PRT-16835) for the system I am describing?
Thank you for any pointers, suggestions, or “got yahs” that you may detect in the proposed system.
You need to measure and state the average and maximum current draw of power-consuming portion of the system, and the amount of time it will be active, and how much time in deep sleep modes.
Also state the operating voltages, i.e. whether everything run directly from the LiPo cell, or if you plan to use DC-DC converters of any sort (which significantly reduces efficiency and increases deep sleep current draw).
Keep in mind that many LiPo chargers do not support load sharing, and require that the battery be isolated from the circuit in order to properly regulate the charging process. That probably will not work for the setup you have in mind. Low voltage LiPo shutdown circuits present yet another problem: some require a manual reset in order to enable charging.
Neither of the Sparkfun LiPo chargers you mention are intended to be used with PV panels.
Finally, re the “Solar Charger - 10 W (PRT-16835)”, heed this warning on the product page: NOTE: While this product is rated at 10W we found the actual max output to be around 3W (5V at 600mA).
Thank you for such a quick and concise reply, JRemington. You have provided sufficient information and insight to prompt me to look into an alternate power source for the project.
I cannot provide the current draw or voltage measurements you asked for since I have not yet breadboarded the project using the Mini Pro and MP3 Trigger boards. I was hoping to use the LiPo battery as the only power source for the two boards (both boards appear to have a Vcc of 3.3 volts) and recharge the battery during daylight hours while still using the battery to power the boards.
Your comments that none of the chargers nor the battery are designed to simultaneously supply energy and recharge at the same time and neither charger is designed to use a solar panel have convinced me to investigate using a 12 volt lead acid battery with a 5 volt regulator as the power source and find a solar charger for the lead acid battery; similar to those used on an RV, only smaller. The allowable footprint for the charger and battery is not highly restricted; the entire system will be housed in an 18" x 48" x 18" enclosed miniature railroad livestock car. The PV panel will be attached to its roof.
I was aware of the 3W max output of the 10W solar panel but felt that would be sufficient for the charger input VA since this project is quite small.
Thanks again for your help and direction, it was greatly appreciated. Sincerely, Jim Armstrong.
A lead acid battery would be my choice too. They are much more tolerant of abuse and for a small project like yours, a special charger is not necessary.
You can trickle charge lead acid batteries using a small 18V “car battery top up” solar panel with a series diode (usually built in) to prevent discharge after sundown. Then the only thing you need to determine is whether the average output of the solar panel, depending on your location, season and weather, is enough to meet the total project power requirements.
Thanks for your concurrence with the lead acid battery. I’m ordering the MP3 Trigger board today so I can do my breadboarding and determine the power requirements before sizing the battery and solar charger. I’m quite confident that a small solar trickle charger with meet the demand. Thanks also for noting that a series diode should be in place to prevent a reverse discharge potential.
One last question about using a USB cable to connect between a USB C receptacle and a USB/USB A receptacle where the USB/USB A board is the driver. Will the Sparkfun USB cable family (CAB-1542X depending on cable length) be the correct choice?
Possibly a MCP73833 based board with a supercap temporary power source that keeps a battery assembly (2 batteries??) charged by flipping back and forth between cells within the assembly.
The primary device runs on power from battery A in the battery assembly,
Supercap in series to buffer any power transitions between batteries.
Battery A gets to a particular set point.
Battery A gets disconnected from Primary device.
Battery A gets connected to Charger circuit.
Battery B is enabled to power Primary device.
When Battery B gets depleted the cycle continues.
I reserve the right to be wrong about any of this. .
Thanks for the idea and it sounds interesting but I have chosen to go an alternate route with a 6 volt sealed lead acid battery and a small RV style solar charger. I basically don’t have any restrictions on space or weight since everything rides around in a miniature railroad cattle car.
I did discover another Sparkfun board called the “Sparkfun Sunny Buddy - MPPT Solar Charger” (PRT-12885) which seems to support a single cell LiPo battery that is connected to both the load and the charger at the same time. That is the type of charger what I was originally searching for but did not find it until after changing over to the 6 volt system.
Thanks again for your input and taking the time to respond.