VFD Conversion Questions

NikolaiBorjeski said:
Does the motor need to be wired differently for 230 vs 460? This is the first dual voltage motor I've played with so I'm new to this stuff. Using an amp clamp the amp draw continues to rise while the RPM goes down, but the VFD doesn't go into current protection.

Would I be fine setting an upper limit restriction on the VFD and just dealing with the lower power output from the motor? For my purposes I'll likely never need all 1HP out of it.
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The motor needs to be directly wired for the voltage you are using, so it would need to be set at 230VAC as the VFD is a 200-240VAC model. The VFD should be directly wired to the VFD motor inputs. Due to the nature of the PWM output, I do not believe an amp clamp will give an accurate reading, but almost all VFD's have the ability to display output volts/amps. The VFD will not go into current protection mode, as it is only outputting what it is set to deliver, as the VFD , as the VFD output is rated at 3/4 Hp.

There are many factors to output Hp, and this only holds at the motor base speed of 60Hz. Below that speed the Hp falls off and torque may stay flat down to 20-30 Hz, but you loose the mechanical advantage. So you have gone from a 6 speed head to a single speed head, with only a 1 Hp motor with a 3/4Hp VFD , the performance will be very anemic over most of the operating range. At say 30 Hz you would be generating maybe 1/3 Hp and also loose the mechanical advantage of 2 for the loss of the belt ratio. If you look at single speed variants of mills with a back gear of this type you would use a 3-5 Hp inverter/vector motor run from 20-200 Hz to cover 500-5000 RPM and a back gear to cover 50-500 RPM.

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Thanks for the info, when I acquired this machine it was missing all of the original belt and motor setup, it does not have a back gear. This is my first mill so I'm completely winging it here. The VFD is wired to a 220v single phase outlet, and the motor is wired directly into the 3 phase output of the VFD. I will double check that the motor is indeed wired for 220 and not 460, but I'm fairly certain it is.

I could change the motor pulley out for a smaller one to gain torque back at the cost of hypothetical RPM, that's a very simple job. I will also keep an eye out for a larger VFD, the one that I have I found cheap so its been good for experimentation but I understand that its too small for this motor. New parts are out of my budget so I'm working with what's available to be on the used market.
 
NikolaiBorjeski said:
Thanks for the info, when I acquired this machine it was missing all of the original belt and motor setup, it does not have a back gear. This is my first mill so I'm completely winging it here. The VFD is wired to a 220v single phase outlet, and the motor is wired directly into the 3 phase output of the VFD. I will double check that the motor is indeed wired for 220 and not 460, but I'm fairly certain it is.

I could change the motor pulley out for a smaller one to gain torque back at the cost of hypothetical RPM, that's a very simple job. I will also keep an eye out for a larger VFD, the one that I have I found cheap so its been good for experimentation but I understand that its too small for this motor. New parts are out of my budget so I'm working with what's available to be on the used market.
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you do realize that most of your cutting is going to be about 1000rpm ?? there abouts. Except if you are cutting with very small diameter tools, then you would need the high rpms. I rarely go to my 3250rpm.. I also added a VFD recently. My lowest is not really where I want it, and neither is my high. But I have different belt combos, so that resolves most issues. I can dial what I need mostly.
Consider a stepped pulley for your needs too. Both spindle and motor. It will help when you need it. But if you need to be at 5000rpm go for it. I don't think you need it. As far as the VFD, you are undersized if you are lower than your motor's rating. I went with a bigger VFD than the motor label, the manufacturer recommended I up it to the next level.
 
NikolaiBorjeski said:
Working on converting my Fray mill to use a 3 phase motor with a VFD. I've fabricated the mount and wired the VFD for testing, and a strange issue has cropped up. With no pulley connected the motor runs up to 100hz without issue, sounds great. When I connect the pulley to drive the spindle however, the motor seems to stall out/slow down after exceeding around 80-85hz or about 5000rpm spindle speed, this is just free spinning, not making chips. In the lower RPM range it makes chips just fine, but at around 5000rpm spindle speed it gives issues.

Belt tension isn't excessive, its just tensioned with a spring. The machine is quite loud when free spinning so maybe the spindle bearings need service? It might also be my idler pulley, its hard to tell. But even with worn bearings it shouldn't create enough resistance to stall a motor. The original brochure of this machine says the spindle is good for 6400rpm, so what I'm asking of it shouldn't be out of line.

I know my VFD is a bit small for this motor, but it should only have an issue under heavy load I would imagine. Maybe I just need a bigger VFD?
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The original brochure information doesn't relate to the currently installed motor nor drive train, it only applies to the spindle capabilities at this point, so let's disregard that for now.

Motors and VFDs are so cheap in the Ontario marketplace that you're wasting your time installing this motor and VFD. You will not coax the performance you seek out of that motor nor VFD. Nothing you can do to the mill will solve the issue.

mksj said:
So a few things, check that the motor is wired for 230VAC. Motor performance falls off after about 90 Hz, you need an inverter vector type motor to go higher w/o having the Hp drop off. The VFD is also too small for the motor size, yes you need a bigger VFD. Also parameter's may not be set correctly, and the motor auto-tune needs to be run with the belt off in dynamic mode. Bearings may also be an issue even though it is rated to higher speeds, may be increase drag and the motor is just running out of power due to the VFD limitations.
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I agree with mksj, except for when he says check the wiring or VFD settings.

Get an inverter rated 2 hp motor with a minimum 10:1 constant torque turndown ratio and a VFD rated at least 1.5 KW.

Then we can address the best practices to setting them parameters and the required pulley ratios to provide you will the full range of speeds at maximum torque.
Try https://www.emotorsdirect.ca/ for a teco westinghouse VFD and a motor or even go cheap amazon VFD and kijiji motor
 
woodchucker said:
you do realize that most of your cutting is going to be about 1000rpm ?? there abouts. Except if you are cutting with very small diameter tools, then you would need the high rpms. I rarely go to my 3250rpm.. I also added a VFD recently. My lowest is not really where I want it, and neither is my high. But I have different belt combos, so that resolves most issues. I can dial what I need mostly.
Consider a stepped pulley for your needs too. Both spindle and motor. It will help when you need it. But if you need to be at 5000rpm go for it. I don't think you need it. As far as the VFD, you are undersized if you are lower than your motor's rating. I went with a bigger VFD than the motor label, the manufacturer recommended I up it to the next level.
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lots of small work requires higher speeds... and with a proper motor and VFD combination attaining the ability to mill and drill at high speeds in easy peasey, and it is clear everything about this set-up needs to be redone if Nikolai is to have a decent machine... so why not hit the RPM the manufacturer designed the spindle to provide? He may not often use the high rpm but when he needs tiny holes in brass and aluminum he wont regret having that speed he needs
 
The pulley sizes you have are really not workable - you can't "gear up" to that extreme without heavy torque losses
unless you have the HP available
 
TorontoBuilder said:
lots of small work requires higher speeds... and with a proper motor and VFD combination attaining the ability to mill and drill at high speeds in easy peasey, and it is clear everything about this set-up needs to be redone if Nikolai is to have a decent machine... so why not hit the RPM the manufacturer designed the spindle to provide? He may not often use the high rpm but when he needs tiny holes in brass and aluminum he wont regret having that speed he needs
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yes, I did say that... but it remains to be seen if he is even doing that. Fine work is not something a newbie can usually do until they have experience. And he never said he was working in small tooling. He just said he wants 5000rpm and was testing to see if torque fell off. With high speed there is no torque usually, not until you are into the big cnc machines. Smaller machines trade torque for speed (as do the big machines but they have plenty of power and amperage).

I would think the goal would be to get a working machine, then push the envelopes. That's a tough machine to work on without the original parts. My first goal would be a working machine, I hope he has a lathe.
 
woodchucker said:
yes, I did say that... but it remains to be seen if he is even doing that. Fine work is not something a newbie can usually do until they have experience. And he never said he was working in small tooling. He just said he wants 5000rpm and was testing to see if torque fell off. With high speed there is no torque usually, not until you are into the big cnc machines. Smaller machines trade torque for speed (as do the big machines but they have plenty of power and amperage).

I would think the goal would be to get a working machine, then push the envelopes. That's a tough machine to work on without the original parts. My first goal would be a working machine, I hope he has a lathe.
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machines last decades, you don't make them or restore them for a single user.

Nikolai, if you dont have a lathe and need any parts made for you let me know. I'm just down the 401 and canada post is reliable. I'd be happy to help you get this running at it's optimal level
 
TorontoBuilder said:
Get an inverter rated 2 hp motor with a minimum 10:1 constant torque turndown ratio and a VFD rated at least 1.5 KW.
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Do you think a motor like this would need a stepped pulley setup? I'm really trying to avoid that as I always find them clunky, I can work it in if needed though.

I'm the meantime I'll install a smaller pulley to make it 1:1 instead of a 2:1 and see what that does. I don't know for sure what I want out of the machine yet, I've never owned a mill before, but I don't want to paint myself into a corner either. I'd like to do whatever I'm capable of to keep the machine operating in its limits.

Again I'm completely green when it comes to 3 phase motors, I appreciate the feedback. I find fabrication fun but calculating numbers for motors isn't my forte.

I have a South Bend 9A that I've used for several years, I'm reasonably confident with it. I was originally on the market for a smaller machine but this one popped up for cheap and I thought it'd be a fun project. This setup will be good enough for me to learn on, once I need more power I'll source a better suited motor and VFD setup. This motor and VFD combo cost me $100, so I'm not super concerned about replacing it in the future.
 
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