Dazza, The dropout voltage for a standard regulator is 2Volts. A 78S09 (the S is a 2A regulator- the ICL7667 require this) regulator will work down to 11Volts but no less. This is fine for a 12Volts system, but when switching to a 24Volts system, which can be as high as 28.5V suddenly, the 78S09...