Your in luck! Cheese @ Bit-Tech has come up with a neat 'piggy-back' device that will allow each of your GPO's to support 32W @ 12V. Click here to check it out. Why did you go for a PCB based approach ...

Variable frequency drives (or VFDs) are widely used throughout industry to provide adjustable speed control of ac motors. Although modern versions are relatively simple to install and operate, VFDs ...