Problem switching on charger with solar panel

Thread Starter


Joined Jul 19, 2018
Hi to all,
I’m trying to find a working solution to this problem. I have solar panels connected to a LiFePO4 battery using an Orion BMSjr with a relay used to connect the panels to the battery. My intention was to have the charging commence as soon as there is light to begin charging. The BMS senses voltage (about 9v) on one pin and switches another pin to activate the relay thus allowing charging, when charging is complete the BMS deactivates the relay circuit and stops the process. The problem is: the solar panels generate enough voltage that BMS senses it and turns on the relay but in low light the panels don’t make enough current to hold the voltage and the BMS drops the relay and a rapid oscillating occurs. I need to find a way to hold out the BMS signal until the panels are really ready to send at least a few amps to the cells


Joined Jul 10, 2017
Use a separate light sensor to measure the light level. A simple CdS photodetector should do the job. You could salvage one from an old solar garden light or buy a ready built unit complete with relay..