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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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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 -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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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. |
#3
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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 |
#4
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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 -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#6
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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 -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
#7
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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). |
#8
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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 |
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