What's the best motor set up?

B

blackboogers

Joined
Jan 16, 2002
Messages
219
I just want to be clear on this. What is the ideal grinder motor set up. AC or Dc and VFD's,etc. I just found out where I work we get 66% off list on Baldor product's. I read something on another post that DC's torque is not as good as AC. What's the best in your opinion. Thanks.p.s. I'm not talking about the grinder itself just what powers it.
 
VFD with a 3ph motor. ....bottom line.

You just get so much more with this set-up. More performance, more reliablity, more safety, more features.

The only draw back is that they can quickly overwhelm the technically challenged.

I have both set-ups in my shop (DC and VFD).


Just my thoughts,
Rob
 
I am running a VFD on my Burr King. It has a 2 hp 3 phase motor. The VFD is a cutler Hammer unit. It was not too bad to set up IMHO. But there was alot of menus and stuff to step thru, but once you got it all you have to do is turn the knob to adjust your speed. Plus you can put in a multiplier so the output does not tell you what frequency you are driving at, but instead tells you rpm, SFPM, or what ever else you want. Well as long as you can figure out the fudge factor and it is a linear relationship to Hz.

I have never worked with dc motors, so I can't really comment on those.
 
Have to agree,VFD with 3phase motor. the torque curve is good thru out the range and like Rob said many features.3phase motors are generally cheaper as well.One note to those who might be confused about 3phase, since most houses do not have it, is that VFD's can be ordered with single phase input and 3 phase output.Dave:)
 
On the very low end of voltage operation DC motors may not have much torque because the controller is limited to a maximum current output (see note 1 below). For example: 12 volts output would require about 62 amps to achieve 1 HP - that assumes the motor is 100 percent efficient and it will not be. The DC motor will serve best for our purposes under load from medium-low to high range. That depends very much, too, on maximum motor RPM and at what DC voltage the motor is rated at for that maximum RPM. For our grinders, a DC motor rated at - say - 4800 RPM at 90 volts would be a very bad choice compared to a motor rated at 4800 RPM at 120 volts. The reason for that is it would require dropping the voltage down too far to get the RPM down low enough. The further the voltage drops the more the HP will drop because of two things: the maximum rated motor current in amps and the maximum rated output in amps of the controller. A 90 volt DC motor at 1800 RPM would be, to me, a perfect choice.

I base this opinion on my limited testing with my system under load while checking current draw and torque and on an electronics background (which had little to nothing to do with motors).

(note 1): except that there are controllers that incorporate torque control. I suppose they monitor armature feedback and automatically vary the voltage output to keep torque constant while under load.

Roger
 
You must log in or register to reply here.
Back
Top