I've got an old milling machine with 3-phase main and table motors which have been running OK from 1-phase supply by means of a rotary converter. In order to reduce the noise and get speed control I decided replace the converter with 2 inverters. The table motor is fine - its speed can be varied from 0 to 200%, but the main motor is odd (to me, any way). Setting the mill gearbox to low speed, the motor speed goes from 0 to 160%, but setting the gearbox to high speed it goes only 0 to
100% before stalling. Other than the gearbox, these are no-load speeds.Because this seemed to me to indicate that the motor was not running at full power I thought that, maybe, it was still wired as star (S) rather than delta (D). With great difficulty (access is very cramped) I have removed the terminal plate, hoping to see 6 terminals that can be arranged as either S or D. There are only 4: 3 phase and a neutral. The resistance between any 2 phase wires is 20 ohms, and between any phase and neutral its 10 ohms. Does this say anything about S or D? I'm in UK, where the 1-phase supply is 220-240v. The motor is 1hp, and the inverter is rated at .75Kw