[janaf]

Hi, this is my first post here,

I am building a machine where I need an

- adjustable speed motor
- around 1.5kW power
- high torque at low speed
- small diameter

An approximate rpm control is enough.

A whole servo motor / driver package is over my budget and has more capability than I need.

A standard asycrone 3-phase motor and inverter would do what I want, except the motor has to large diameter.

So I started thinking of using a 3-phase AC servo motor with a frequency inverter. What characteristics does it take from each, motor and driver, to get this to work? Do I need a vector drive?

I do not need exact positioning or even exact rpm controll. I would need overcurrent monitoring and overtemperature monitoring.

Any input on this would be appreciated

[Al_The_Man]

There are not many options for running a AC or BLDC off of a VFD.
The Hitachi line of induction motor VFD's advertise it is possible, but when I contacted them they mentioned that there is quite a bit of engineering integration to use it and I would need to supply them with all the motor data first.
Another couple of alternatives is the BLDC BSM controllers made by Baldor, or use a Servo controller such as Advanced Motion type.
When using an AC servo motor it would need to have BLDC type commutation on it for it to work with these drives.
Al.

[janaf]

Thanks,

well, maybe the whole idea is not that good...

I did find some 3-pahse asynchone motors with servo-like power/diameter, like CEG-EM/L so that may be a better way.

I also found that Lenze 8400 have what they call Sensorless control for synchronous motors (SLPSM) but there is a lot of fineprint, "optimal performance only with matched Lenze motors", "the nameplate data and equivalent circuit data of the motor (motor leakage inductance and motor stator resistance) are entered manually", max frequency is 650Hz, (still quite a lot), temperature feedback is a must, only supported on the latest rev 10.00 driver etc..

So my best option now is either to find a cheapo complete servo motor with driver or a compact asycronous motor, or redisign my machine to fit a standard asyncrone motor.

[mike_Kilroy]

Hi, this is my first post here,

I am building a machine where I need an

- adjustable speed motor
- around 1.5kW power
- high torque at low speed
- small diameter

so define these relative terms.... WHAT exact max rpm? What exact torque?

u might consider a cheapo SMALL ac motor into a gearhead to get the speed down, torque up and still use a $ 200 vfd......... but u gotta give details for more ideas....

[Al_The_Man]

Another alternative to consider is pick up one of the more quality treadmill DC motors off ebay and use one of the KB/Baldor SCR drives.
If your requirements are not that demanding, it is a cheap way to go, and a DC motor has all the torque you need down to zero rpm.
For a little bit extra the 4 quadrant types will give you +-10vdc control and dynamic braking if you needed it. They also have a tach feedback for really precise control.
Al.

[janaf]

so define these relative terms.... WHAT exact max rpm? What exact torque?

u might consider a cheapo SMALL ac motor into a gearhead to get the speed down, torque up and still use a $ 200 vfd......... but u gotta give details for more ideas....

It is for a small tooling lathe, there is no exact specification. A lathe basically needs constant output power at variable speed ie torque in inversely proportional to speed (force and speed at the cutting tool tip is appr constant, regardless of the diameter worked at). I would want something like between 200rpm up to 4000rpm.

Traditionally this was solved with a mechanical gearbox, with maybe 3-10 speeds. With a good mechanical gear I would probably need around 300-400W power.

With a 300W motor and 200rpm mechanical gear, would give around 15Nm torque, and at 4000rpm, around 0.7Nm

So my best guestimate is that without mechanical gear I'd be happy with something like 1.5-2kW. This should give, intermittently, enough torque at low speed, and more than enough at high speed.

Or I will have to make a low / high speed gear :-|

[Al_The_Man]

DC motor would do it although 1:1 would be around 2500rpm max. unless gearing is involved.
Al.

[janaf]

Thanks, I will take a look at the treadmill motors and drivers.

[asuratman]

Hi Al,
One question for you, I have AC servo motor 4.5kw, I want to use it as spindle motor. What should I do to make motor turning? What needed to control speed RPM?

[janaf]

Same situation as me, except I do not have the motor :-)

You can of course use a "proper" servo drive, or the same replies as below should apply?!

[Al_The_Man]

Hi Al,
One question for you, I have AC servo motor 4.5kw, I want to use it as spindle motor. What should I do to make motor turning? What needed to control speed RPM?

That a big motor, Unfortunately AC sinusoidal motors are the hardest to mix and match drives due to the various commutation used, many use resolvers which also vary in output etc.
One way is to put an encoder on with hall effect equivalent commutation pulses, you need to know the pole count of the motor and to align the encoder correctly to the respective stator winding, this can be done with a double beam scope.
You then need to obtain a suitable sized BLDC controller such as made by A-M-C. drives. Their 100amp peak model would do it, but not cheap.
Al.