Hi Rye_84,
The supply voltage and the resistive divider determine the output
voltage of the circuit. (12 volt supply voltage and two 30k resistors.)
Therefore if you increase the supply voltage to 24 volt the output
voltage of the circuit will increase to 12 volt.
But there's a small problem, there allways is . . .
If the load gets 12 volt the transistor also gets 12 volts across it's
terminals, multiplied by the output current and it gets hot !
This may not be a significant problem when using this circuit at 12
volt but if you power it with 24 volt . . . and it's a waste of energy too.
However you could connect a second load in series with the collector
of the transistor, the transistor would only heat up during sunrise and
sundown. During the night no collector current, during the day (virtually)
no collector emittor voltage and therefore no dissipation in the transistor.
Personnaly I would replace the 741 with a fet input opamp with a higher
output current, this is needed to drive the transistor in or close to the
saturation region.
And why did the original designer didn't think about this ?
Because he's an idiot !
You might not get the result you expect because a led is not a lightbulb.
on1aag.