Hardinge motor mystery (to me)

Gentlemen:
I'm looking at the motor in my Hardinge TM to determine the requirements
for a VFD or phase converter.
The motor is a Diehl 220 V., 3 phase, two speed motor. The spec plate
lists the current draw as:
1720 RPM 3/4 HP 2.3A
875 RPM 3/8 HP 3.2A
What is causing the to motor to suck up an (almost) additional Amp at
the slower speed? I can understand that multi speeds would require some
design compromises, but that seems like a lot of inefficiency.
Kevin Gallimore
Reply to
axolotl
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The motor is a Diehl 220 V., 3 phase, two speed motor. The spec plate lists the current draw as:
1720 RPM 3/4 HP 2.3A
875 RPM 3/8 HP 3.2A
What is causing the to motor to suck up an (almost) additional Amp at the slower speed? I can understand that multi speeds would require some design compromises, but that seems like a lot of inefficiency.
The motor is a one winding, "consequent pole" motor, in which its six total wires are operated either: 1) three connected to the source and three open-circuited, or 2) three connected to the source and three short-circuited.
It is a contant torque motor.
Permanently connect the motor in high speed mode and then permanently connect the VFD to the remaining three motor leads.
You will have to bypass the motor starter as there should be no contacts between the VFD and the motor.
Simulate the functions of the HI/LO lever and FWD/REV lever using microswitches which are input to the VFD.
Reply to
Peter H.
It's not inefficiency as such. The larger number of poles in the half-speed configuration results in more leakage reactance (caused by magnetic field going directly between the poles on the stator instead of via the rotor). This leads to a lower power factor, which leads to a higher current. Base the invertor size on the larger current if you intend to use the low speed switch or just run in high range all the time and let the invertor do the work.
HTH Mark Rand RTFM
Reply to
Mark Rand
That explains it. Pretty slick for 1947.
Is it considered good practice to have a local disconnect before the VFD?
Thanks,
Kevin Gallimore
Reply to
axolotl
You can likely use the contacts in the existing switch stacks and retain the use of the levers. While they are not immediately intuative, its easy to determine which contact is open or closed.
The usual thing that goes wrong with those Hardinge switch stacks is the roller and spring that detent it into the various positions falls off when the spring breaks. Easy enough to reform the loop that broke and reinstall.
Gunner
"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke
Reply to
Gunner
Understatement of the week.
If I were wiring one of these, I would use the fwd/off/rev lever to run the VFD for those functions. Then I would turn the high/off/low lever into center-off, momentary switch, and use the drum switch contacts for that lever into the VFD control lines, as speedup/slowdown.
Most VFDs allow that kind of two-button fast/slow speed control programming.
Jim
Reply to
jim rozen
Is it considered good practice to have a local disconnect before the VFD?
Well, the VFD probably provides all the motor running protection you're likely to require, but as the HP is under 1, you could use the flexible cord itself as the disconnect.
Now, on a 7.5 or 10 HP VFD retrofit (Monach 10EE, for example), you'd still require the fusible switch disconnect.
(Although I am familiar with the Hardinge TL, and I own one, the other variations of the split bed toolroom lathe are less familiar to me. Please post photos of yours to the DropBox, if you don't mind).
Reply to
Peter H.
LOL..indeed.
Not a bad idea, or use low for a programmed speed such as 1000 rpm, which most of us use most of the time. Least..I do. Shrug.
Gunner
"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke
Reply to
Gunner

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