Kirk Wallace wrote: > On Wed, 2007-10-31 at 20:15 -0600, Jon Elson wrote: > >>Kirk Wallace wrote: >> >>>What is the best way to drive a 4hp, 90VDC, 40A spindle motor on a >>>Hardinge CHNC? Some of the large DC motors I have seen, look like >>>universal motors which would operate on AC or DC. Does anyone know if >>>the CHNC spindle motor could work on AC? I'm thinking, a few dimmer >>>switches in parallel and a stepper to turn the dials ;). I wonder if it >>>would be cheaper to go with a 3-phase motor and VFD. Thanks. >> >>No, these motors are NOT universal motors. You could rectify >>the mains to drive the motor, but then it would draw 40 A from >>the line. You should be able to find an SCR drive for this. >>You can't parallel dimmers, they can't be trusted to give the >>same pulse width. > > > I was joking about the dimmers. So far I have found this: > > http://www.baldor.com/products/detail.asp?1=1&page=1&catalogonly=1&catalog=BC155&product=DC+Controls&family=One+Way%7Cvw%5FDCControls%5FOneWay&voltage=180 > Yes, but as a 5 Hp drive for 180 V motors, it is a 20 A drive. Also, I'm pretty sure it is a single-quadrant drive, so it will provide no braking. That may be a problem. > but this puts out 180V and I need 90V. Plus it seems that this kind of > controller does not interface with a computer well at all. I'm pretty sure there would be a way to adapt it for computer control. It may, or may not, require the pot connection to be isolated. There are ways to do that. It's > beginning to look like DC lathe spindle drives are a specialty item, > which means, hard to find and big bucks to buy or repair. > Well, you need a DC motor drive, not necessarily a DC "spindle" drive. A true DC servo spindle drive would be a four-quadrant servo amp. That would work quite well, too. But, servo axis amps at 40 A are less common, but they do exist. > >>If it is a standard-frame motor, then you >>could go the 3-phase and VFD route. That may not give you the >>range of speeds and torque required. > > > The newer VFD's are much better with this aren't they? No, not if the DC motor was designed to produce rated HP over a 5:1 speed range. This is the problem with the Monarch 10EE, for instance. There was only back gear and direct drive, all other speed control was done with the motor. So, it had a fairly modest HP rating, but could deliver it from something like 20% to 200% of nominal speed. An off-the-shelf AC motor can't do this, no matter what the VFD is capable of delivering. You get a linear power ramp from zero power at zero speed to rated power at rated speed, then linear power to however much you want to overspeed the motor. The DC motor way with a high-torque motor replaces the belt drive or gearbox, the AC motor just can't replicate that low-end torque, unless you put in a FIVE times higher HP motor.
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