VFD Conversion Questions

[NikolaiBorjeski]

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?

 

[mksj]

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.

 

[NikolaiBorjeski]

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.

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.

 

[woodchucker]

that motor pulley does not look correct to my limited knowledge .. you look like you are using a way to big fan pulley, and a very undersized spindle pulley. Where'd you get your pulley sizes from?

 

[benmychree]

What is going to keep the pulley in position when the quill is changed in its vertical position? I have the same machine, but with its original drive system.

 

[woodchucker]

What is going to keep the pulley in position when the quill is changed in its vertical position? I have the same machine, but with its original drive system.

changed or moved John?

 

[NikolaiBorjeski]

The motor rpm goes up to around 3000 or so, I wanted to aim for a max rpm of around 6000 so I got a motor pulley that was twice the diameter of the spindle pulley, giving me that rpm range. I was just going to run it to see if it killed the torque. Might end up being an issue, might not.

As for the spindle pulley and quill, the pulley is not directly connected to the spindle, it's on a splined shaft so the Quill can move up and down without affecting the pulley

 

[woodchucker]

The motor rpm goes up to around 3000 or so, I wanted to aim for a max rpm of around 6000 so I got a motor pulley that was twice the diameter of the spindle pulley, giving me that rpm range. I was just going to run it to see if it killed the torque. Might end up being an issue, might not.

As for the spindle pulley and quill, the pulley is not directly connected to the spindle, it's on a splined shaft so the Quill can move up and down without affecting the pulley

but what holds it in position while you are moving it up and down? Mine moves up and down using a spline too, but my housing keeps the pulley from moving. There's a complex (not too) setup that keeps the pulleys rotating on the housing while a plate on top of them allows the spindle to engage the spline. the plate is attached to the pulleys.

 

[NikolaiBorjeski]

The shaft that the pulley is attached to is pressed into bearings that are then pressed into a steel flange that is bolted to that cast aluminum housing. When I got this machine it already had the factory setup removed, so I don't know what it looked like originally, there's very little info on these machines out there.

 

[benmychree]

changed or moved John?

Nothing changed, lived here in the same place for 52 years. Only thing changed is old age has set in!

The shaft that the pulley is attached to is pressed into bearings that are then pressed into a steel flange that is bolted to that cast aluminum housing. When I got this machine it already had the factory setup removed, so I don't know what it looked like originally, there's very little info on these machines out there.

I wasn't thinking, the original pulley does not move on those splines as shown in your picture, the quill splines are below the deck, the upper splines have to do with the back gears I think they are contained within the pulley, but it has been a long time since I had it apart.