Motor types on a lathe

[Roger Chandler]

The question that Scott Haddix raised about the Revo lathe from Laguna got me wondering about motor configurations on a lathe. My Grizzly G0698 has a DC brushless motor........they changed that to an A/C motor on the next iteration G0733........I have wondered why a number of times.

I found this information on Brushless DC motors.........

http://www.howstuffworks.com/brushless-motor.htm

According to them there are many advantages to a brushless DC motor, including more torque and better control of the efficiency because of the computer components and less wear.......no brushes to replace, no sparking, less noise...........runs cooler. The only disadvantage listed is the higher initial cost.

I am wondering if this info on dc brushless motors comports with the understanding of others here who use lathes with an A/C motor and inverter? Any advantages of an A/C motor on a lathe?

[Roger Chandler]

Doing further reading on this website.......

http://www.slmti.com/brushless.asp

they state other advantages.......safer in explosion prone areas [think dusty areas] safer around liquids, no brush residue on the internal components, making them need less maintenance,[ better for bearings inside the motor, etc.] better control for speed, higher inertia [torque] and a smaller dc brushless motor can accomplish the same load requirements as a larger A/C motor.

I am just wondering then why the manufacturers of most lathes are using higher maintenance A/C motors on their lathes, if these advantages are so prominent? Is it just a matter of cost? Then perhaps being able to sell replacement parts later on?

Hummm........:confused:

[Dennis Ford]

Brush-less DC motors have all of those advantages over single phase motors and brush type DC motors. Three phase AC motors have most of the same advantages and cost less.

[Roger Chandler]

Further exploring the motor types on a lathe..........is there an advantage for the 3 phase A/C motor with an inverter that runs it off single phase a/c power over the d/c brushless motor run by an inverter?

issues such as start up torque, and torque under load, etc. Efficiency in power output and efficiency in power consumption? Speed variations and available torque for our purpose?

Perhaps someone with an engineering degree or understanding can answer these issues.

Additional: Do 3-Phase a/c motors have brushes? Seems I read about electric car technology somewhere that mentioned the stator being laminated so that conductors produce the alternating current..........I am not certain of that, but if anyone can explain the benefits/advantages of each type, then that would be great!!!

[Roger Chandler]

Brush-less DC motors have all of those advantages over single phase motors and brush type DC motors. Three phase AC motors have most of the same advantages and cost less.

Dennis ........I was typing my last post while yours posted........second time today that has happened! :o

If you will, read my post above and if you know any answers to my questions, please share your knowledge! thanks!

[Fred Belknap]

Roger I read your post a couple days ago and you said your G0698 has a DC motor. I still have mine in the shop and I checked on the motor and I don't see anything that says it is a DC motor. It says 3 phase, 220volt type F. The type F I think pertains to the working temperature. The 3520B has basically the same motor spec wise but it's physically a lot larger motor. They are both rated at 2 hp. I haven't had any problems with the Griz motor, it doesn't even get very warm. I am curious where you found that it was a DC motor.

[Roger Chandler]

Roger I read your post a couple days ago and you said your G0698 has a DC motor. I still have mine in the shop and I checked on the motor and I don't see anything that says it is a DC motor. It says 3 phase, 220volt type F. The type F I think pertains to the working temperature. The 3520B has basically the same motor spec wise but it's physically a lot larger motor. They are both rated at 2 hp. I haven't had any problems with the Griz motor, it doesn't even get very warm. I am curious where you found that it was a DC motor.

I think the F type is for continuous duty, Fred. I read somewhere that the motor was D/C brushless............don't remember off the top of my head, but I think that is correct. The manual that came with the lathe only says 220V 2 hp.

If it says 3 phase........I wonder if that is the motor or the inverter setup? Perhaps what I read.......maybe it was wrong. Information on the web is a crap shoot for the most part.......I would like to know if the motor on the 0698 is D/C or A/C 3 phase! I am going out to the shop to look at mine.........

I just looked at mine.....the label says 3500r/min which means the motor spins at 3500rpm.........likely it is d/c because to get the slow speeds we can on the lower end [less than 100 rpm] it would require a controller. which I believe is the configuration of our G0698. If I have my thinking incorrect on this, I am certainly open to someone correcting, but I believe this to be so..........

[Jeff Gilfor]

For a very good discussion of the differences (as they apply to autos anyway), see: http://www.teslamotors.com/blog/induction-versus-dc-brushless-motors

You certainly can find argument in favor of both types. Generally though, BDCM are less reliable in the long run than 3PAC. For a given size (physical that is), 3PAC motors have more low speed torque (their torque-speed curves are rather flat). BDCM are somewhat more energy efficient, as they carry their own permanent magnets, while 3PAC motors have to generate the magnetic field (uses current and wastes some as heat in doing so). The controllers for 3PAC motors can be expensive and difficult to program (if you do it yourself), not so much for the BDCM.

Most of the big lathes use the 3 phase AC motor (3PAC motor). Must be a reason huh?

[Dennis Ford]

3 phase motors do not have brushes, I can not answer the other questions.


Further exploring the motor types on a lathe..........is there an advantage for the 3 phase A/C motor with an inverter that runs it off single phase a/c power over the d/c brushless motor run by an inverter?

issues such as start up torque, and torque under load, etc. Efficiency in power output and efficiency in power consumption? Speed variations and available torque for our purpose?

Perhaps someone with an engineering degree or understanding can answer these issues.

Additional: Do 3-Phase a/c motors have brushes? Seems I read about electric car technology somewhere that mentioned the stator being laminated so that conductors produce the alternating current..........I am not certain of that, but if anyone can explain the benefits/advantages of each type, then that would be great!!!

[Roger Chandler]

3 phase motors do not have brushes, I can not answer the other questions.

Thanks Dennis!

[Jeff Gilfor]

Both 3 phase (or single phase) AC AND brushless DC motors are without brushes.

The real advantage of the 3 phase motor, is that it is less expensive and has better service life. Additionally, although a BDC motor will have less startup current and more torque at the design RPM, they do not have a flat torque curve, the torque drops off rather steeply on either side if the design speed. For an escalator, the DC motor is best (single speed, high torque, lower electricity costs), for something like a lathe, AC is the way to go.