using a 1140RPM motor with VFD

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sherwood.ih.lucent.com says...

Unless you're actually experiencing problems operating the lathe--not enough power on heavy cuts, for example--I wouldn't bother. It's not unusual for the VFD to indicate that the motor current is near nameplate current even when lightly loaded. It's not necessarily an indication that the motor is producing rated power, but rather is operating at low power factor, which is typical of lightly loaded motors.
I've tried without success to use a VFDs current sense as an indication of overload on a conveyor. The difference between normal load and gross overload, short of stalling the motor, was not large enough to sense reliably.
Ned Simmons
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I have experienced the same. I look at the motor current and then load the machine and I only see very small changes. Therefore I question the VFD current display.
I have had my mill kick out on overload when drilling (high load) at very low freq(10Hz). I think it has seriouly derated the motor at that speed though.
chuck
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    Hmm ... mechanical variable speed mechanisms are not very efficient -- lots of friction losses in that variable-speed belt.

    Well ... my 12" Clausing step pulley lathe has a 1-1/2 HP motor, and I think that is a good fit for it. Your 11" would not need quite as much horsepower, but the variable-speed pulley will require more to drive it properly, so I think that I would consider the 1-1/2 HP at a minimum, with perhaps the 2 HP which your switch and contactor suggest being the better choice.
    Good Luck,         DoN.
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Rule one. Never throw anything out.
Rule two. Have lots of room, for rule one.
Jim
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Charles A. Sherwood wrote:

You're aware that most VFDs when fed from single phase power must be derated to 75%?
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derated
On older VFD's this is generally true, but almost all of the new VFD's rated for 3 HP or less are designed to run full output power with only single phase input power.
Also, I agree with Gunner, yank out the mechanical vari-speed drive and run the motor direct using the VFD for speed control. I did this on my Clausing 5914 and it works great. You need to pick your motor pulley size carefully- I picked mine so that when the motor is double speed the lathe is at its top rated spindle speed. By the way, this is a real easy conversion to do on a 5914 since the spindle already has a toothed belt pulley on it- make a new motor plate, use the existing motor plate brackets moved up to the upper slots, buy a new motor pulley and belt and you're done.
You don't get full HP at lower spindle speeds, but you don't have the losses (and noise) from the mechanical vari-speed anymore (which aren't small) so power generally won't be an issue.
Good luck-
Paul T.
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Its seems aweful silly to remove a prefectly good working Mechanical VS drive. Yes, it makes a little noise and it wastes a little power but it works just find and give more flexability than using the VFD alone. I have a VFD on my mill and DC motors with speed controllers on my lathes but I don't think they give quite enough adjustment range to be used with only one belt speed. chuck
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I find for general prototyping and small production run work, the "constant torque" provided by the VFD is fine at the lower spindle speeds (versus the "constant horsepower" that a mechanical vari-speed tries to provide which gives you even higher torque at low spindle speeds). If I was pushing my lathe and mill to the max cutting capabilities at the lower spindle speeds perhaps the VFD would be limiting.
But with a 2HP motor on both my lathe and mill, I've never had any need for more power at the lower speeds using the VFD's. I set up both VFD's to run from 20% underspeed to 200% overspeed, giving me a 10 to 1 speed range. Add in the back gears and that a very wide speed range on both machines.
But if you're happy with your mechanical vari-speed drives, stick with them. In my case on the Clausing, I didn't like the extra noise and maintanence hassles. On the Bridgeport I was tired of changing belt pulley settings, but I didn't realize how much I would like the automatic spindle braking and quick reversing until I had it.
Paul T.
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I disagree. This is a new Teco VFD sold by dealers electric and is rated for 2HP with single phase input.
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I'm not particularly knowledgeably about electrics, but couldn't you just tong one of the motor leads to see what the ACTUAL current is?

parameters
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    A clamp-on ammeter will probably show the same thing that the VFD's readout shows. The problem is that the current is out of phase with the voltage, so only a percentage of it is actually doing work. This is called the "power-factor", and an accurate power measurement requires measuring the voltage and the current and the phase shift between them. The clamp-on ammeter will measure *only* the current.
    As the motor gets closer to full nameplate power being delivered, the phase shift will reduce so the current will bear a closer relationship to the power being delivered.
    The VFD *could* calculate the power, as it has both the voltage and the current data -- but nobody seems to bother to program them to do so -- and in terms of heating the motor windings and fuse blowing or circuit breaker tripping, as well as power lost heating the external wiring, the current alone is what really matters.
    Enjoy,         DoN.
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No no no no. Think about it. The VOLTAGE is essentially constant at all loads (120 V, 240 V or whatever the wall socket is giving). If the power varies, the only way it can vary is by varying the current. I think there's something wrong with your lathe, motor, or VFD current meter to give flat current response regardless of load. Big lathes often have ammeters to indicate load. These would be ineffective if the meter always read the same value. The VFD on my 11" 3 HP lathe shows 2.8 A at no load and climbs to 13 A at full load (then trips on overload :-( ).

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In article <9866af06.0310011228.3f2aa297

You're not only ignoring the issue of power factor mentioned in several other posts, but also the fact that the voltage output by the VFD varies with frequency. The simple VFDs we're talking about here are often referred to as volts/Hz drives beacause the voltage output when running below base speed is proportional to frequency. For example, the drive will deliver 24V @ 6Hz, when set up for a 240V 60Hz motor.
Ned Simmons
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Ned Simmons wrote:

The Allen Bradley 1305 seems to have some sort of feedback loop running, it makes adjustments based on what it thinks is the actual motor speed.
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wrote:

In the A-B's I'm using, you can select closed or open loop. For my applications, I run open loop. I provide my own control loops external to the drive. I don't know if the 1305 has the same feature or not.
Pete Keillor
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In article <3yJeb.2364$oX5.1292572
says...

Sounds like what is often referred to as a "sensorless vector" drive. True vector drives use an encoder or other feedback device to sense rotor velocity and sometimes position.
Ned Simmons
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For testing, I borrowed a 1HP Teco VFD from my surface grinder. I decided to buy a 2HP Teco VFD dedicated to this machine so that I can use a bigger motor if I need it. For now, I suspect the existing motor will work ok. I still think that an 1200 RPM motor would give me a big increase in low speed torque and if I find a cheap one I will try it out.

It hums. I started using a custom VF curve and started the motor out with a higher percentage and I made it start reliabily. I think the default it 5% and I pushed it to 20% to make it start well. However I think this means I should not operate the motor at too low a freq or it will burn out the motor.

The VF curve change solved the problem. I also enabled a torque boost but that didn't seem to make much difference. The VFD will also tolerate an overload for 1 minute.
thanks for the advice! chuck
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