Do I need to use an iron core iron or can I just use copper coils? Let me be more specific.I know that I need to use magnets.The question is ,when I wind my copper generator coils,do they need to be wrapped around an iron core or will just copper coils work? Let me be more specific.I know that I need to use magnets.The question is ,when I wind my copper generator coils,do they need to be wrapped around an iron core or will just copper coils work?