Hi Chris,

I converted one of my lathes to 3-phase 4 pole motor, using an inverter to supply the 3-phase. The motor I bought can run at both 50Hz and 60Hz so running your motor at a higher frequency than 50Hz should not be a problem. I regularly run my motor over 60Hz, and after more than a decade I have had no problems. A 4 pole motor should be able to give more torque than a 2 pole as long as you don't turn the frequency too high.

Thor

Edited By Thor 🇳🇴 on 13/07/2023 18:09:42

I regularly run my setup at 75 hz, no issues. I'd go for 4 pole.

Are you getting confused by the inverter setting for a 50Hz supply or a 60Hz supply as some countries have. Here in the UK you would set the inverter up for 50Hz. The speed settings are a different parameter & in many cases can be set from 0 to over 100Hz. My Myford is set at about 60-65Hz max Which in the right gear runs just over 2000rpm.

I would not want to run it at this speed & usualy it never gets taken above 1000. Yes the motor cage is the same for a 2 pole & a 4 pole motor ,so not much chance of doing any damage overdriving it. Definately a 4 pole as the 2 pole will stall out under load. 2 pole motors are usually found on fans. Or any machine that does not require high torque.

Steve.

I was busy last night and missed this thread:

I recently fitted a 3 phase motor and VFD to my ML7 and after asssessing all the parameters I fitted a SIX pole motor and a larger (75mm) pulley on the motor.

The 6 pole motor is even smoother and quieter than a 4 pole, has more torque (for the same power) and the larger pulley is kinder on the belt. Even with tension off, the old belt would take a slight set around the motor pulley adding to noise and vibration when started.
It helped that the NOS 1/2 HP (0.37 kW) 910 RPM TEFC motor was only £40. A 1/2HP 3 phase motor is more than enough power for an ML7. The Gamak 6 pole I got is larger than a typical 0.37kW 4 pole to provide the torque so is very rugged.

The motor construction is identical to the two and four pole so is rated to the same speeds. Generally best use is made of a VFD when using it to run the motor at higher than rated (nominal mains frequency) speed. A modern inverter rated 4 motor will typically be good to at least 120Hz and a 6 pole to 200Hz but check the datasheet.

A two pole motor is not an viable option for the ML7. It's too fast and less smooth due to increased torque ripple. This can actually be seen in the surface finish of turned items.

Robert.

10 amp, or 13.. Noel

While Noel's answer isn't wrong per-se, he does not have the required information to determine the fuse size required. The fuse in the plug is there to protect the cable. So to know the rating you need to know the size of the flexible cable used. If a 13A fuse is fitted then 1.25mm2 or 1.5mm2 flex must be used. If 1mm2 flex is used then a 10A or smaller fuse must be fitted.

While noting that a 2.2kW VFD is a bit oversized for a 0.75kW motor, a 5A fuse would be adequate for the actual load of your system. I would still use 1.25 or 1.5mm2 flex for the mains input though. This is to minimise voltage drops. The VFD try to supply the required power so if the voltage drops the VFD will draw more current causing more voltage drop. This can lead to instabilites and reduced performance. Ideally you would use a 13A fuse in the plug with 1.25mm fleax and then put a 6.3A T ceramic fuse in the VFD enclosure before the mains filter.

Robert.

Robert is correct in his comment and I had made the fatal mistake of assumption – that in wiring up a machine tool one would use at least 1.5 flex or cable. I tend to use 2.5 flex but that is because I can, though things get tight in some 13a plugs !

Chris, to find the sectional area of a wire or flex take 1 strand accurately measure the diameter in mm then use the formula Pi R squared. If a single conductor then that will be the answer, if flex then multiply the answer by the number of strands. Since in the main there are standard sizes of flex or cable if the answer looks near it should be right – or way out and obviously wrong ! Good luck. Noel.

I'd leave the maximum frequency (speed) at 65Hz. This gives you a bit more operating speed range but is well within the limits of your 50/60 Hz motor. As an aside, often the best utility can be had from a motor/VFD set up by arranging for the motor to run at higher speed than it's name plate rating. This is why I recommended, and fitted on my own ML7, a 6 pole motor. On a VFD this motor can easilly run at 4 pole motor speeds. It has the same rotor, bearing and fan construction as the 4 pole. It prodces more torque at low speeds than a 4 pole. I also fitted a larger motor pulley to reduce stress on the belt.

The revolution for 50 Hz probably only affects the RPM indication or parameters set in RPM. It should be set to the value for your motor but does not affect actual operation of the motor.

Robert.