RPM rating for VFD conversion

Looks like one heck of a motor.

i do wonder why its says only rated to 80 Hz. looks to me like it should go 200 Hz (4000 RPM). So, you might be taking a chance running it up there. that said, I've run every motor this fast on VFD. My thinking, they are all made about the same inside and never heard of the cheaper two pole motors failing at 3600 - surely 10% over is no big deal.

it is possible to find VFD motors rated for 6000 RPM
 
There needs to be a distinction between vector duty and inverter duty. Sometimes those terms are used interchangeably but a vector duty will have a 1000-1 constant torque ratio so torque holds to basically 0 hz. Inverter duty will have more like a 10-1 or 15-1
ratio which limits the low end torque. A vector duty motor will also hold hp to about 90 hz before dropping off so it has a little more grunt on the high end as well. Both types can be run at a higher hz but performance suffers as the hp and torque drop off is steep.

The motor listed above is a 254 frame size so likely larger than you can fit into a 10ee case and given the plate ratings, I don't think it will outperform a vector duty 7.5-10 hp 1800 rpm 213 frame motor. Price is good but no back gear means the motor needs to perform at a range of 0-120 hz and most inverter duty motors are not designed to operate as well as a vector motor. Dave
 
The issue is several fold, a 1200 RPM motor will be limited as to the maximum RPM, and you will plain just run out of Hp and applied torque to the spindle w/o a back gear. The torque is a function of the motor torque and the mechanical ratio. The 6 pole washdown motor has a constant torque ratio of 10:1, so assuming you are belting it to a 1:1 ratio and say 6 Hz to 120 Hz would give you a speed range w/o a back gear of 120-2400 RPM. But at 6 Hz, your 7.5Hp motor will have a 0.75 Hp rating. Without the back gear it will be very anemic and probably not that usable below 200 RPM. A 4P vector motor in this size range can be run to 5000-6000 RPM, so a usable frequency range of say 10-200 Hz, and you could do this with a 2:1 belt ratio. this would give you a usable speed range of 100-3000 Hz, as well as a higher mechanical advantage. Above the motor base speed a inverter/vector motor can retain full Hp up to its maximum speed, where standard motors start to fall off around 90-100 Hz. There is also a range of inverter rated motors as to their performance window, in general an inverte motor can be run across the line with or w/o a VFD, a vector motor can only be run with a VFD. Both inverter and vector motors can operate at near 0 speed (constant torque of 1000:1 or greater), a vector motor can have more precise speed control and "0/low speed" speed torque (see attached Baldor description). High performance inverter vector motors tend to be TENV or TEBC, and not TEFC. This has to do with the thermal dissipation ability when operating at the RPM extremes.

There are quite a few threads on 10EE conversions to 3 phase, but w/o the back gear anything below 10 Hp can result in lackluster low end performance. Incorporating the back gear, most conversions use a 5 or 7.5 Hp. Incorporating the back gear requires precise machining of a gearbox interface adapter plate, I recently spoke to another person that did this conversion and he indicated that you needed to have a precision of 0.0005" to maintain the proper gear spacing. If you look at the current production Monarch 10EE they use a 7.5Hp motor with an encoder feedback, as well as a 5:1 back gear reduction to achieve a 25-4000 RPM speed range.
https://monarchlathe.com/products/lathes/toolroom/monarch-ee-series#

If you are planning a 3 phase motor conversion, a 4P inverter/vector type motor offers the greatest speed range as well as the widest performace window in this type of motor. Common replacement motors are the Marathon Blackmax and Bluemax, Baldor IDNM/ZDNM, Reliance, Lincoln, Leeson and other motor manufactures also have their inverter/vector models. You need to look for a motor with a constant torque ratio of 1000:1 or higher as well as a maximum speed of around 3X the base speed (180-200 Hz). This is just a starting point, there are many other build factors to consider.
 

Attachments

  • Baldor Vector-Duty-Motors-Drives.pdf
    1.9 MB · Views: 10
A friend up the road simply mounted the gearbox to the end of the new motor.

He is retired machinist with not so good electrical but great machine skills.

Fixtures all on a surface plate for perfect alignment and it looks factory.

So everything past motor are factory.

Smaller motor so much better as most operations do not need huge power, shift to back gear when needed.

The lathe is smooth and powerful.



Sent from my SM-G781V using Tapatalk
 
I thought I would share some pictures of my 10EE VFD conversion. It’s a 1968 modular machine with a maximum speed of 4,000 rpm. My conversion retained all of the original controls including the ELSR, and I also retained the original back gear. I chose to use a Black Max 7.5 hp with encoder in a closed loop system. The drive I used was a Nidec M701 with an interface module. And it also has a 20-ohm 1,500 watt brake.

I decided to retain the 4,000 rpm and to change pulleys to 1:1. This increase in drive rpm does not only have ramifications for motor rpm and hertz but also there are some drive considerations that have to be addressed and even modified. I would be happy to expand on this or the gear box adaption and motor modifications that are necessary to make this all work smoothly.

I also had a chance to compare the performance side-by-side with a 1952 10EE motor generator that I also did some restoration on. The drive in it was in excellent shape and original. I could also talk about this if there is interest.

IMG_0346.jpg IMG_0347.jpg IMG_0348.jpg IMG_0349.jpg IMG_0354.JPG IMG_0336.jpg IMG_0330.JPG
 
You might want to start a new thread but I'd be interested. I think I saw some of it on PM but would like more details. Mark here is doing a system for my CVA which is a geared 10ee clone made in the UK so the details and needs are much different but knowledge is power.

The benefit of the encoder and closed loop system is something I've heard of ,but am not familiar with so those details would be helpful. Also how accurate are the cuts and did you need to have any spindle or way work done. Dave
 
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