Hardinge TM motor amp draw too high
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  1. #1
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    Default Hardinge TM motor amp draw too high

    Hi all

    I have a 1940s steel dial hardinge TM mill with a 230v-only, 2 speed 3ph motor. I hooked it up directly to a 220V single phase input VFD(Yaskawa GPD-205) using the high speed wiring (leads 4,5 and 6 to VFD, 1-2-3 tied together),and I have everything up and running.

    I've noticed the motor isn't perfectly happy. The FLA for the high speed should be 2.4amps, but the VFD shows around 3amps when idling at 60hz. It rises during a cut - minimally during small to medium cuts, but up to 8 amps for heavier cuts - and the VFD overload fault happens frequently of I keep going. If I try to go above 60hz, the motor will speed up but the amp draw also rises. At 80hz, it draws around 4.5 - 5amps at idle. Above 80hz, the motor doesn't like it at all, and the speed actually starts to drop off.

    I've played around with the belt tension, but it doesn't seem to make much difference. The jackshaft in the base was cocked a little, which I corrected and did see a small improvement, but only to the numbers I gave above.

    With the belts off, the bearings in the motor, jackshaft and spindle all felt quite smooth and there's no real bearing noise.

    I have two thoughts:

    1) the motor is on its way out. It came from a medical device / prosthetics lab, and was covered in a thick layer of plaster of Paris dust when I got it. I'm wondering if that schmoo has somehow damaged the motors innards....

    2) the VFD needs some more adjustment. I've looked through the manual, but not sure how to tune it any better than I have it now. The V/Hz ratio can be adjusted, but I've no idea where to start with that, or if that's even necessary.

    Hoping there's a somewhat simple answer to this - the mill is otherwise ready to put to work!

    Thanks in advance for any suggestions,

    Lee

    Sent from my SM-N960U using Tapatalk

  2. #2
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    for what it's worth...

    my uk versions of the um , I've had two, were factory fitted with 1.5 and latterly 2hp motors. When running off of a vfd, the 1.5hp struggled to run it at full speed because the vfd limits

    the 2hp vfd and motor seems underpowered given the rigidity of the machine.

    my guess is that hardinge was happy to let the smaller um motor work harder than rating (which it will when mains powered) because the duration of the cut can never be that long , it's a small mill!

    Vfd's do tend to mollycoddle the motors

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    Huh, that's a very interesting observation... So, what I'm seeing with the factory 3/4hp motor may not be that unusual? It seems weird that the idle amp draw is higher than the FLA...

    Although, I agree that the 3/4 hp motor seems underpowered...

    As an example,
    With a 2" carbide insert facemill in the spindle, I can take a 0.050" full width cut in mild steel, and can basically push the cutter through the cut as fast as I can crank. Amp draw runs into the 4-4.5amp range.
    If I up the cut to 0.075" the amp draw shoots up, and the motor starts to bog down heavily. I'm not seeing any vibration from the machine - just the motor bogging.

    Is this about on par with others' experiences?

    Lee

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    [QUOTE=leeko;3468270]

    (leads 4,5 and 6 to VFD, 1-2-3 tied together)

    Leeko,
    How confident are you of the above wiring to obtain high speed? I'm facing a similar conversion on a TM and am trying to determine the motor lead configuration. The factory wiring diagram is little help.
    Jim

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    Hi Jim

    This is right on the backside of the motor


    And the leads were labeled clearly. My first thought was maybe it was wired 440v, but this motor doesn't have that option - it's 220v only

    Lee



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    Lee,
    Thanks for that. Meanwhile I decoded the wiring diagram for a 1948 TL lathe which uses the exact same motor as the subject TM has. It also uses the same wiring scheme as your mill: L1-T4, L2-T5, L3-T6 and T1-T2-T3.

    So I guess no issues as to your wiring connections. Sorry I can't usefully comment on your amperage situation. I can think of no good reason you should get amperage readings that high if everything is in good order. Are you using the VFD digital readout for those amp readings or a clamp probe on the motor leads?

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    Hi Jim

    They're coming directly from the VFD. As I understand it, 3 phase amperage readings aren't reliable from a regular old multimeter like I have

    Any thoughts on the cuts that I described above? It seems like I can move much more metal with the carbide insert cutter, than I was able to with the 1" HSS cutter on the arbor and overarm support... But maybe I'm just way off in terms of what I'm asking of the machine? Still trying to get to grips with its capabilities!

    I'll try to post a video later today

    Lee



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    Wait - are you reading the currents from the VFD display, or are you using a DVM, an amp-clamp meter, or an analog simpson type meter?

    A DVM or an amp-clamp will not read the waveform on the leads correctly. Not clear an analog meter would do so either. The
    waveforms are non-sinusoidal.

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    Using the VFD display.

    Sent from my SM-N960U using Tapatalk

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    Good, that's the one way you are sure to get a good number. Most of those two speed hardinge motors
    are pretty bullet-proof. Your wiring of course is correct. Unless you have other reasons to believe
    the motor is in trouble (smoke, heating, fire....) I would just keep on using it.

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    Hey not an electrical type guy here but. It is a 2 speed motor. If you have your vfd hooked up to the high speed winding. And you have the low speed windings wires tied together would cause a problem. The faster you spin the motor the more the low speed windings try to put the brakes on. Try not tieing the low speed wires together. Tape the wires so they are not in contact with anything. High speed the motor is 3/4 hp and low speed is 3/8 ph correct? Let us know if this helps.


    Not sure if my thinking is correct here but are the 2 speeds on completely different sets of field windings. If so if you are running off one set of windings is the other set of windings getting electricity produced in them? If so and the set of windings are wired together isn't it causing a short circuit or magnatizm in that field? Would this then work in a conflict with the other set of windings?
    Last edited by mastuart; 02-29-2020 at 05:49 PM. Reason: adding something

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    Hi,

    Thanks for the suggestion. But, for high speed the motor wiring plate shows 1-2-3 tied together.

    As someone who knows almost nothing about motors and electrical fields, I would be hesitant to run it any way other than what the wiring diagram shows....

    Lee

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    Quote Originally Posted by leeko View Post
    Hi,

    Thanks for the suggestion. But, for high speed the motor wiring plate shows 1-2-3 tied together.

    As someone who knows almost nothing about motors and electrical fields, I would be hesitant to run it any way other than what the wiring diagram shows....

    Lee

    Sent from my SM-N960U using Tapatalk
    It's only 3/4 HP?

    Too easy by half to just go and find a ONE speed motor of 2 HP - even 3 HP - that likes the VFD better. 1 or 2 HP if DC, 2 or 3 HP if AC.

    Ex: A six-pole Marathon Inverter-Duty should give you decent low-end and respond "well enough" to higher Hz as well.

    Keep in mind that regardless if Dee Cee or 3-Phase+Vee Eff Dee, any motor put into variable-speed service works better at it with a reserve of 1 1/2 to 2 or more times the nominal nameplate HP of a one-speed.

    Any given "nameplate" is ordinarily the designed-in goal of sweet spot - a motor's best all-around point.

    Move away from that, one or more parameters degrade - efficiency high on the list.

    IOW... ANY jiggery-pokery to run it well-away from its nameplate "base" RPM has trade-offs of one or more kinds.

    So a 3 HP motor won't be asked to deliver 3 HP on a TU or TM mill. The toolholding system can only put about 1 1/2 HP to work in any case.

    By comparison, a modest Burke #4 doesn't have nearly as nice a knee- any axis - as the Hardinge. But with a # 9 B&S spindle, it CAN put more HP to the tooling.. more than the tiny ways can stand, if pushed too far..

    Mostly the reserve assures that you have 1 HP to 2 HP "wherever" you need to run it in the RPM band so as to hold the cutting rate right where you dialed it to be.

    Protection from both electrical overload or undue mechanical stress is then set into the DC Drive or the VFD's onboard limits.

    Only with that comfortable reserve does actual USE, not theory, then get "smile-and-forget" easy.

    2CW.. Dee Cee mostly, even so.


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