batteriescircuit analysissolar cellswitchesvoltage-regulator
Is this [dead link removed] correct?
Think of it as a power bank. The 10 V input is a solar panel.
How is the battery and solar panel connected?
The site say that when the switch is open, solar panel charges the battery. When the switch is closed, does the solar panel and battery together power the load? Is it in parallel?
Just use some low-voltage-drop diodes, such as Schottky diodes, to ensure that the battery will not try to energize the solar cell.
simulate this circuit – Schematic created using CircuitLab
Here, the solar cell is represented using the photodiode symbol D1, which is the closest thing available in the schematic editor. Current can flow from the photocell only if it develops a voltage which exceeds that of the battery by at least about 0.25V, a difference that is needed to forward-bias the Schottky diode D2. When this condition does not exist (for instance, the light is too low), then the Schottky is not forward biased and prevents the reverse current flow from battery to D1.
Here is a version of the above schematic which incorporates a more detailed discrete component model of the cell:
When the load is off, the panel will fill the battery with the voltage above permitted for the chemistry of the battery, the electrolite in the cell will boil (gassify) and destroy the battery.
When the load is on, both battery and panel will provide current. Of course the panel will work less efficiently if the output voltage of the panel isn't held on maximum power point voltage.
Best Answer
Yikes. That site is icky.
You cannot simply connect 10 V to a LiPo battery. That is a good way to get an explosion/house fire/sad battery/sad you. LiPo batteries (and several other battery chemistries) require CC/CV charging, meaning they need constant current charging up to a float voltage, and then constant voltage charging after.
Another issue is that you cannot simply connect a solar panel to the input of that circuit. Solar panels do not provide a fixed voltage (it varies with sun intensity) and operate with poor efficiency unless you put in a little extra effort to do maximum power point tracking.
It sounds like you want to build a solar-powered battery charger circuit. Luckily, there are existing solutions that make this task easy. There are many ICs that are both MPPT controllers and multi-chemistry battery chargers. For example, the Linear LT3652, which is suitable for small panels/smallish batteries (max charging current 2A). As is characteristic of Linear parts, the datasheet is quite good and provides a wealth of information on how to design for various battery chemistries and load configurations.