This is the simplified system:
- a battery (3.6 V, 2450 mAH, NiMH)
- a solar panel (max 5.2 V, 157 mA)
- a wall charger (5 V, 2100 mA).
The battery is constantly being drained, but very slowly (85 mWh per day).
The solar panel produces 62.5 mWh per day on an average day (7 hours of low sun at only 8,000 lux).
This sustains the system for a little over a year if we assume everyday is an average day (without solar the batteries drain in a few months).
The wall charger is only used once a year to quickly replenish the batteries back to full, so the system can last another year.
Every few years the batteries will have to be replaced.
I want these scenarios to happen:
- If wall charger is not plugged in, trickle charge battery with solar panel only.
- If wall charger is plugged in, stop charging with solar panel and fast charge the battery only with wall charger.
How do I switch between the two scenarios?
Best Answer
You can use a Schottky diode in series at the charger and solar panel and then connect them both to the battery. The drawback is a ~0.3V drop on the diode. Not a problem in case of the charger, but will reduce the power output of the solar cell. On the other hand - smaller PCB area, cheaper and more reliable.