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


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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.

On Sat, 11 Sep 2004 13:40:39 -0400, axolotl wrote:

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.



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

Peter H. wrote:

It is a contant torque motor.

That explains it. Pretty slick for 1947.

You will have to bypass the motor starter as there should be no contacts
between the VFD and the motor.

Is it considered good practice to have a local disconnect before the VFD?

Thanks,

Kevin Gallimore


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On 11 Sep 2004 20:18:52 GMT, inch (Peter H.) wrote:



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.

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

In article , Gunner says...

You can likely use the contacts in the existing switch stacks and
retain the use of the levers. While they are not immediately
intuative, ...

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


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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).

On 11 Sep 2004 16:44:56 -0700, jim rozen
wrote:

In article , Gunner says...

You can likely use the contacts in the existing switch stacks and
retain the use of the levers. While they are not immediately
intuative, ...

Understatement of the week.

LOL..indeed.

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

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