I have a 2.7V 100F super-capacitor. I am going to be charging it with a 6V 1W solar panel. Now the solar panel only puts out 6V when it is receiving the best sunlight so this means the output from the solar panel can be lower. What is the best way to go about charging the super-cap. I was thinking of just using a voltage divider with resistors but I wanted to get some other opinions.
Even for the simplest schematics, simple resistor is not enough. You definitely want a series diode to prevent capacitor discharging INTO solar panel when it is dark, as well as some way to prevent capacitor from being overcharged -- either zener, red/yellow LED, or a shunt regulator. In fact, once you have a protection circuit you no longer need a resistor divider -- just charge at max power and let regulator dissipate any extra power. This gives the following schematics:
"OVP" may be:
- a 1W, 2.0 V zener (zeners generally have high voltage tolerances)
- 1W red/yellow LED
- 2 regular diodes in series (each has about 0.7v-1v voltage drop, two would regulate to 1.5-2V)
- diode + transistor shunt regulator