a motor is only rated at 5hp at its rated rpm..... 5hp at 2500rpm, hence it provides around 10.5 ft lb of torque....
power = 2 X pi X N X T / 60 (sorry I think in metric to have to convert back and forth....) 10.5. ft lb at 200 rpm is around 0.4 HP..... an AC motor (or DC motor, not servo / stepper) should not be run at very low rpms, I believe the guidance is about 30% of its normal rated rpm, given you need to still cool the windings. (search Google and do some reading) so at 2500rpm rated speed, you should not really go below 750rpm (you are trying to run at 8 to 10%!) a DC motor also is voltage proportional rated.... I am guessing that its rated at 220V DC so at 200 rpm it will be running at about 17.6V. if you switch to an AC drive with a VFD then your problem on minimum rpm will be similar (have a search on Google about vfds and minimum rpm). for full speed control.... use a servo (as I do).... that will give you full and precision control..... again you are limited by the math of Power = 2 x pi x N X T / 60 On Mon, 26 Jul 2021, 23:55 Earl Weaver, <[email protected]> wrote: > Hi, > I have a lathe spindle with 8 in. chuck that is run with a 5HP Reliance > DC Motor and Reliance DC Drive. > I just cannot get much power out of it at low RPM. Was trying to turn > 8in OD steel, at approx. 200 -250 RPM with .005 in. cut. It didn't work, > it just stalled. > When I run it at low RPM the chuck rotation is movable, not firm. > I can take a hold of the chuck and hold it and move it back and forth as > it rotates. > It also is more noisy at low RPM. > > This lathe is a Linuxcnc retrofit with J Elson's Universal PWM > Controller and DAC Spindle control. > The DC drive has tachometer feedback from the motor. > I have tried numerous times to adjust, tune the drive, without success. > I also tried closed loop control from the spindle encoder within LCNC, > also no success. > > So here come the questions: > Should I keep trying to get this DC Drive working or would it be better > to switch to AC Variable Frequency Drive? > If I would switch to AC VFD would 5HP AC Motor be sufficient size for > existing 1:1 ratio double v belt to drive 8" spindle chuck? > What torque at low RPM can I expect for this 5HP DC motor? am I > expecting to much from it? > Would there be a better drive option for the existing DC motor? > Any recommendations? > > Thanks, > -- > Earl Weaver > Email: [email protected] <mailto:[email protected]> > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
