And yes, I know a modern solution is to use a VFD. I'd just gotten an old lathe, so two tools in the shop are three phase. Also I found that the capacitors really should be switched as the load demands. Even though it was rated for a 5hp motor, and I'm using a 3hp, the contacts on the relay would often weld together and the starter caps weren't taken out of the circuit.
I've set a bank of 40uf/440v capacitors up and a potential relay. My research started with the likes of this paper. I've started building a single to three phase converter.
