# 240v 1ph Servo Drive with output to 3ph 380v?

Do these exist? Iv only seen ones where i/o is either 240v or 380v. So can a 240v in & out servo drive work to any extent if its driving a 3ph 380v PMSM motor, if so what and Im interested in the math here, Im guessing the amps are a limiting factor? Im aware of the three ns=120*fq/#poles equations/variations and same with torque BUT im always missing the link between current & volts, I should be able to tell how this motor will perform in relation to its original spec. The two most important being speed and torque. Basically 'will it work?' and 'what will the speed+torque be?'. (all nominal stuff) If I give you, from the motor, the -

• rated torque = 5.3nm
• rated speed = 5000rpm
• rated current = 5.5a

How would the original spec above change?

Here is the relevant part of the datasheet:

• No. They don't exist, a motor supply voltage can't be higher than input supply voltage. The next thing is that such motor would have approx. 3kW and it's just too big to be powered from single phase. Jun 10, 2021 at 5:51
• OK, I took a chance. I looked at your recent posts and pulled the datasheet info from them and added it to this question. If I did wrong, you can always revert the edit. But I felt that you weren't really understanding how this motor is rated. Jun 10, 2021 at 6:49
• Yes thats fine, cheers. Jun 10, 2021 at 10:56

There is a relationship between voltage and speed. If you supply the motor with a lower voltage, your maximum speed will be limited. Looking at the datasheet, there are actually three separate ratings based on different temperature requirements.

In what the datasheet calls an insulated installation, here are the ratings to maintain less than 60 degrees temperature rise over ambient:

Power: 800 W Speed: 4000 RPM Voltage: 283 V (RMS) Current: 1.7 A (RMS) Torque: 1.7 Nm

If you are unable to supply 283 V (RMS) you will not be able to achieve 4000 RPM. It will scale somewhat linearly. So 240 / 283 * 4000 = 3400 RPM.

So 5000 RPM is probably not going to happen at 240 V. But 3400 RPM may be doable.

At lower speeds, though, full torque should be available. But if you plan to run continuously without ventilation for the motor, you should plan to keep the torque at or below 1.7 Nm, regardless of speed. You can get much higher torque at low RPM for short times, even with a 1 kW drive. The motor is capable of MUCH higher torque, but this will tend to heat up the stator windings, and if you are not able to remove that heat, you will run into problems.

You really need to spend some time reading the whole datasheet and trying to understand it. If there is part you don't understand, ask a question about it, highlighting the relevant part.

• Iv sort of rushed into this situation on an impulse buy and discovered how complicated it can be and requires a much deeper understanding which ATM I havn't got the time but also I want to test these motors after they arrive instead of having three 9kg paper weights around the house. Hmm, Im using this for a small lathe so this aint gonna be usable. If I up the torque via pulley my speed will be too low and if I keep the speed theres a higher chance of burning the motor. You really can't get blood from a stone! (for want of a better analogy) 10lb of muk in a 5lb bag maybe. )) Thanks. Jun 10, 2021 at 10:49
• Ok so a smart choice is to get a 240v VFD that can be used with a PMSM. This way I can test these motors, although I won't be using them, then Ill source a more suitable induction motor or a synchronous motor with the typical DC stage. (however likely that is on a budget) Jun 10, 2021 at 11:17
• Experimenting with them will be great. That will honestly be the best way to determine how much torque you can get out of them. I wouldn't be suprised if you can get 5 Nm for 5 minutes or something like that. But I wouldn't plan on 5Nm for 5 hours unless you have a blower on the motor (which could solve all your problems, by the way). Jun 10, 2021 at 18:00
• I thought heat seemed to be the most limiting factor, Thats good to know, thanks! ) Jun 12, 2021 at 11:10