# FVD and Motor Advise



## HARRY304E (Sep 15, 2010)

Buttonwoodworks said:


> Gentlemen, Let me start by saying I am an experienced electrician with a Journeyman card. That being said, my strengths are Schools, light commercial, and residential (construction, rehab, maintenance). But when it comes to motors, I shamefully admit that Motors are a weakness.
> 
> Now the background….. I am an avid wood turner. I have a heavy duty Craftsman Lathe that I dont use anymore because the bearings have slight radial free play. It has a "Developed 2HP DC Motor". I want to turn this thing into a log spinning beast. Replace the bearings. And replace the DC motor with a 2-3 HP AC Motor. I also want to control the speed without having to change belts, so I believe a VFD woud achieve this. The current DC motor has a pot to control speed.
> What type of motor and VFD would you recommend for this application?
> ...


These guys should be able to help you.:thumbsup:

http://driveswarehouse.com/?gclid=C...u-9SKPk319BXDwkKffzkSXYAkK0Kl5QxuNqHNBQfw_wcB


.


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## eric7379 (Jan 5, 2010)

Buttonwoodworks said:


> Gentlemen, Let me start by saying I am an experienced electrician with a Journeyman card. That being said, my strengths are Schools, light commercial, and residential (construction, rehab, maintenance). But when it comes to motors, I shamefully admit that Motors are a weakness.
> 
> Now the background….. I am an avid wood turner. I have a heavy duty Craftsman Lathe that I dont use anymore because the bearings have slight radial free play. It has a "Developed 2HP DC Motor". I want to turn this thing into a log spinning beast. Replace the bearings. And replace the DC motor with a 2-3 HP AC Motor. I also want to control the speed without having to change belts, so I believe a VFD woud achieve this. The current DC motor has a pot to control speed.
> What type of motor and VFD would you recommend for this application?
> ...


Just how big of a log are thinking about putting in there?? The very first thought that comes to mind when you say this is "Are you nuts?"



HARRY304E said:


> These guys should be able to help you.:thumbsup:
> 
> http://driveswarehouse.com/?gclid=C...u-9SKPk319BXDwkKffzkSXYAkK0Kl5QxuNqHNBQfw_wcB
> 
> ...


I think there is much more involved that just a simple link drop here, Harry. Depending on the "log" size, I would seriously question whether or not a lathe designed for the home user is beefy enough for what he is describing. Safety, to me, would be a huge consideration in an endeavor such as this. 

Much more involved too than just replacing the original bearings. Those bearings were spec'd and installed for the anticipated loads. Now you are wanting to put logs on it?? Sorry, but I highly doubt that the new bearings will last long at all.


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## varmit (Apr 19, 2009)

Mechanical issues aside, a VFD will only work with a three phase motor. There are plenty of VFDs that will operate on a single phase input and provide a three phase output.


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## JRaef (Mar 23, 2009)

I took the "log spinning beast" comment as a metaphor, not a literal description... In any wood lathe your work piece size is limited by the head stock height and bed length. A typical Craftsman lathe could not hold anything it cannot handle (without major mechanical modification).

Buttonwoodworks,
As was said, if you want variable speed, get a 230V 3 phase motor and a VFD that will take 230V single phase input, then put out 230V 3 phase for the motor. That capability is inherent in modern VFDs. Up to 3HP those are very very common and most of them can do the phase conversion without needing to be de-rated, but check first to make sure. You can often get motors like that locally on Craigslist that you can drive over to pick up (eBay usually involves significant freight because motors are heavy), then there are plenty of websites selling that type of VFD very inexpensively. 

Just steer clear of the cheapest ones that don't show a brand name, or if you can read the name Huanyang on the photo. Those are total crap from China being dumped here by fly-by-night resellers on FleaBay who disappear before the warranty claims come in, and the mfr in China is totally disinterested in supporting sales outside of China through them because those are all surplus scrap that was dumped.


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## micromind (Aug 11, 2007)

Also to add to the other posts, a motor powered by a VFD will apply more torque to the load when it it turning fairly close to its normal speed. 

In other words, if the motor is designed to run at 1725 RPM and it is directly coupled to the load and operating at 50 RPM it will have far less torque than it is running at 1500 RPM and the load is turning at 50 RPM.


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## HARRY304E (Sep 15, 2010)

eric7379 said:


> Just how big of a log are thinking about putting in there?? The very first thought that comes to mind when you say this is "Are you nuts?"
> 
> 
> 
> ...


Considering I'm dummy on this topic the link is something I could use to bump his thread and hope others would reply---looks like I got it done


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## JRaef (Mar 23, 2009)

micromind said:


> Also to add to the other posts, a motor powered by a VFD will apply more torque to the load when it it turning fairly close to its normal speed.
> 
> In other words, if the motor is designed to run at 1725 RPM and it is directly coupled to the load and operating at 50 RPM it will have far less torque than it is running at 1500 RPM and the load is turning at 50 RPM.


Hmmm... I'm trying to figure out what you are trying to say here. Are you meaning to compare final torque of a 50RPM load driven directly by a VFD vs torque at a load driven by a pulley that brings the final speed down from full speed at the motor to 50RPM? If so, then yes, you are correct. But it's not because the VFD creates LESS torque at lower speeds, it allows the motor to produce the SAME torque at lower speeds. However when you change the final speed by changing the pulley ratio, you MULTIPLY the torque at the same ratio in which you DIVIDE the speed. So the net effect is what you described, I just wanted to make sure others don't misunderstand why. 

VFDs do not reduce torque, but neither do they increase it like speed change methods that utilize mechanical advantage.

Generally, you do not need the increased torque at low speeds on a wood lathe, which makes VFDs an ideal solution. On a metal lathe however, that may be exactly the opposite depending on the working material or task. I always tell people when putting a VFD on machining tools to leave the mechanical speed change systems in place for that reason, then use the VFD to do fine adjustments.


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## micromind (Aug 11, 2007)

JRaef said:


> Hmmm... I'm trying to figure out what you are trying to say here. Are you meaning to compare final torque of a 50RPM load driven directly by a VFD vs torque at a load driven by a pulley that brings the final speed down from full speed at the motor to 50RPM? If so, then yes, you are correct. But it's not because the VFD creates LESS torque at lower speeds, it allows the motor to produce the SAME torque at lower speeds. However when you change the final speed by changing the pulley ratio, you MULTIPLY the torque at the same ratio in which you DIVIDE the speed. So the net effect is what you described, I just wanted to make sure others don't misunderstand why.
> 
> VFDs do not reduce torque, but neither do they increase it like speed change methods that utilize mechanical advantage.
> 
> Generally, you do not need the increased torque at low speeds on a wood lathe, which makes VFDs an ideal solution. On a metal lathe however, that may be exactly the opposite depending on the working material or task. I always tell people when putting a VFD on machining tools to leave the mechanical speed change systems in place for that reason, then use the VFD to do fine adjustments.


I need to work on my writing skills.......lol.

Yes, I meant more torque by running the motor at a higher speed and reducing the speed (belt, gearbox, etc.) at the load. 

The motor produces roughly the same torque at any RPM, but it is multiplied by turning the load slower than the motor.


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## JRaef (Mar 23, 2009)

micromind said:


> I need to work on my writing skills.......lol.
> 
> Yes, I meant more torque by running the motor at a higher speed and reducing the speed (belt, gearbox, etc.) at the load.
> 
> The motor produces roughly the same torque at any RPM, but it is multiplied by turning the load slower than the motor.


Thought so. It's a worthy point to bring up, a lot of people don't follow that thought process through when applying VFDs to replace gearboxes or pulleys to change speed. They may know that torque is increased when you change the ratio, but they don't carry that idea through on how that differs from changing the speed with a VFD. Then they find out the hard way when the load stalls the motor, and they THINK it's because the VFD reduced the torque. 

Not a week goes by when I don't get a call along those lines from someone who did it. They invariably understand how speed ratio changes work, they just fail to think it through all the way.


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