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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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using a 1140RPM motor with VFD
A while back I bought a Rockwell 11 inch lathe with a mechancial variable speed drive. This drive works well but seems to have a lot of friction. The lathe came with the original 1HP 3PH motor. I installed a 1HP VFD and I managed to make the lathe run. The VFD could not start the lathe unless the Mechancial VS was set to less than 1/2. I Adjust some parameters in the VFD to increased the starting torque which pretty much solved the problem. However the VFD indicates the motor is drawing nearly full current just turning the spindle at max RPM. And yes the spindle bearings are fine! The original motor starter was set up for a 2HP motor even though the lathe only has a 1HP motor. Its very difficult to read the motor tag inside the lathe cabinet and the front swithc say 2HP, so the electrician probably put on a 2HP contactor with 2HP heaters. So anyway I am considering installing a larger motor. I found some 1.5 HP 1140RPM motors fairly cheap. I think the lower RPM motor will develop more torque and the VFD will still allow me to achieve full spindle speed by increasing the freq to 90. I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is that the lower speed motor will develop more starting torque and I can still get the same spindle speed by increasing the freq on the VFD. For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5) where the existing motor will only develop 1/2 HP(900/1800) at the same RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will develop more low end torque that a 2HP 1740 RPM motor that I was originally considering. what do you think? chuck |
#2
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using a 1140RPM motor with VFD
In article , cas@w-
sherwood.ih.lucent.com says... I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is that the lower speed motor will develop more starting torque and I can still get the same spindle speed by increasing the freq on the VFD. For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5) where the existing motor will only develop 1/2 HP(900/1800) at the same RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will develop more low end torque that a 2HP 1740 RPM motor that I was originally considering. what do you think? 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 |
#3
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using a 1140RPM motor with VFD
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. 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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using a 1140RPM motor with VFD
In article ,
Charles A. Sherwood wrote: A while back I bought a Rockwell 11 inch lathe with a mechancial variable speed drive. This drive works well but seems to have a lot of friction. The lathe came with the original 1HP 3PH motor. I installed a 1HP VFD and I managed to make the lathe run. The VFD could not start the lathe unless the Mechancial VS was set to less than 1/2. I Adjust some parameters in the VFD to increased the starting torque which pretty much solved the problem. However the VFD indicates the motor is drawing nearly full current just turning the spindle at max RPM. And yes the spindle bearings are fine! Hmm ... mechanical variable speed mechanisms are not very efficient -- lots of friction losses in that variable-speed belt. The original motor starter was set up for a 2HP motor even though the lathe only has a 1HP motor. Its very difficult to read the motor tag inside the lathe cabinet and the front swithc say 2HP, so the electrician probably put on a 2HP contactor with 2HP heaters. So anyway I am considering installing a larger motor. I found some 1.5 HP 1140RPM motors fairly cheap. I think the lower RPM motor will develop more torque and the VFD will still allow me to achieve full spindle speed by increasing the freq to 90. I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is that the lower speed motor will develop more starting torque and I can still get the same spindle speed by increasing the freq on the VFD. For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5) where the existing motor will only develop 1/2 HP(900/1800) at the same RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will develop more low end torque that a 2HP 1740 RPM motor that I was originally considering. what do you think? 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. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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using a 1140RPM motor with VFD
Charles A. Sherwood wrote:
A while back I bought a Rockwell 11 inch lathe with a mechancial variable speed drive. This drive works well but seems to have a lot of friction. The lathe came with the original 1HP 3PH motor. I installed a 1HP VFD and I managed to make the lathe run. The VFD could not start the lathe unless the Mechancial VS was set to less than 1/2. I Adjust some parameters in the VFD to increased the starting torque which pretty much solved the problem. However the VFD indicates the motor is drawing nearly full current just turning the spindle at max RPM. And yes the spindle bearings are fine! The original motor starter was set up for a 2HP motor even though the lathe only has a 1HP motor. Its very difficult to read the motor tag inside the lathe cabinet and the front swithc say 2HP, so the electrician probably put on a 2HP contactor with 2HP heaters. So anyway I am considering installing a larger motor. I found some 1.5 HP 1140RPM motors fairly cheap. I think the lower RPM motor will develop more torque and the VFD will still allow me to achieve full spindle speed by increasing the freq to 90. I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is that the lower speed motor will develop more starting torque and I can still get the same spindle speed by increasing the freq on the VFD. For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5) where the existing motor will only develop 1/2 HP(900/1800) at the same RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will develop more low end torque that a 2HP 1740 RPM motor that I was originally considering. what do you think? chuck You're aware that most VFDs when fed from single phase power must be derated to 75%? |
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using a 1140RPM motor with VFD
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? "Charles A. Sherwood" wrote in message ... A while back I bought a Rockwell 11 inch lathe with a mechancial variable speed drive. This drive works well but seems to have a lot of friction. The lathe came with the original 1HP 3PH motor. I installed a 1HP VFD and I managed to make the lathe run. The VFD could not start the lathe unless the Mechancial VS was set to less than 1/2. I Adjust some parameters in the VFD to increased the starting torque which pretty much solved the problem. However the VFD indicates the motor is drawing nearly full current just turning the spindle at max RPM. And yes the spindle bearings are fine! The original motor starter was set up for a 2HP motor even though the lathe only has a 1HP motor. Its very difficult to read the motor tag inside the lathe cabinet and the front swithc say 2HP, so the electrician probably put on a 2HP contactor with 2HP heaters. So anyway I am considering installing a larger motor. I found some 1.5 HP 1140RPM motors fairly cheap. I think the lower RPM motor will develop more torque and the VFD will still allow me to achieve full spindle speed by increasing the freq to 90. I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is that the lower speed motor will develop more starting torque and I can still get the same spindle speed by increasing the freq on the VFD. For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5) where the existing motor will only develop 1/2 HP(900/1800) at the same RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will develop more low end torque that a 2HP 1740 RPM motor that I was originally considering. what do you think? chuck |
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using a 1140RPM motor with VFD
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#8
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using a 1140RPM motor with VFD
On Wed, 01 Oct 2003 00:54:28 GMT, "ATP"
wrote: Charles A. Sherwood wrote: A while back I bought a Rockwell 11 inch lathe with a mechancial variable speed drive. This drive works well but seems to have a lot of friction. The lathe came with the original 1HP 3PH motor. I installed a 1HP VFD and I managed to make the lathe run. The VFD could not start the lathe unless the Mechancial VS was set to less than 1/2. I Adjust some parameters in the VFD to increased the starting torque which pretty much solved the problem. However the VFD indicates the motor is drawing nearly full current just turning the spindle at max RPM. And yes the spindle bearings are fine! The original motor starter was set up for a 2HP motor even though the lathe only has a 1HP motor. Its very difficult to read the motor tag inside the lathe cabinet and the front swithc say 2HP, so the electrician probably put on a 2HP contactor with 2HP heaters. So anyway I am considering installing a larger motor. I found some 1.5 HP 1140RPM motors fairly cheap. I think the lower RPM motor will develop more torque and the VFD will still allow me to achieve full spindle speed by increasing the freq to 90. I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is that the lower speed motor will develop more starting torque and I can still get the same spindle speed by increasing the freq on the VFD. For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5) where the existing motor will only develop 1/2 HP(900/1800) at the same RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will develop more low end torque that a 2HP 1740 RPM motor that I was originally considering. what do you think? chuck You're aware that most VFDs when fed from single phase power must be derated to 75%? Pretty much true. Or even lower, depending on manufacture and age of the unit (Ie the older ones are not as efficent as the newer bleeding edge ones) Gunner "If I'm going to reach out to the the Democrats then I need a third hand.There's no way I'm letting go of my wallet or my gun while they're around." "Democrat. In the dictionary it's right after demobilize and right before demode` (out of fashion). -Buddy Jordan 2001 |
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using a 1140RPM motor with VFD
In article ,
Jon Grimm wrote: 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? 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. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#10
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using a 1140RPM motor with VFD
In article , Gunner says...
Pull the variable speed crap out, and run it direct drive. It will be smoother, quieter and easier on your VFD. Stick the stuff in a box so you can include it with the lathe when you upgrade to a different lathe. Rule one. Never throw anything out. Rule two. Have lots of room, for rule one. Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
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using a 1140RPM motor with VFD
You're aware that most VFDs when fed from single phase power must be derated to 75%? 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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using a 1140RPM motor with VFD
You're aware that most VFDs when fed from single phase power must be derated
to 75%? I disagree. This is a new Teco VFD sold by dealers electric and is rated for 2HP with single phase input. |
#13
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using a 1140RPM motor with VFD
Also, I agree with Gunner, yank out the mechanical vari-speed drive and run
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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using a 1140RPM motor with VFD
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 :-( ). This is NORMAL, believe it or not! The problem is the current sensors in the VFD only read current, not power. The inductance of the motor is such that it draws nearly constant current at all loads, but the phase angle changes dramatically. So, the motor draws roughly 3 A at idle, to 3.5 A at full load, but the power draw goes from, perhaps, 1/4 Hp at idle to 1+ Hp at full load. My mill with a 1 Hp motor works exactly the same way. It also has nothing to do with the VFD. |
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using a 1140RPM motor with VFD
Ned Simmons wrote:
In article 9866af06.0310011228.3f2aa297 @posting.google.com, says... 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. 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 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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using a 1140RPM motor with VFD
In article 3yJeb.2364$oX5.1292572
@news4.srv.hcvlny.cv.net, says... Ned Simmons wrote: In article 9866af06.0310011228.3f2aa297 @posting.google.com, says... 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. 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 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. 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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using a 1140RPM motor with VFD
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 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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using a 1140RPM motor with VFD
I think you will end up needing a new VFD, too!
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. What does it do when it fails to start? 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. If the VFD can be set for higher than nominal amps, try setting it as high as it will go. 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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