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Variable Frequency Drive

Bill Blue

Platinum Level Sponsor
I am converting my 12" Enco lathe to VFD. Bought a 1 hp, 1720 rpm, 3 phase WEG motor on Ebay. I can best sum things up by saying "it is and it isn't" Yes, it is a new, purdy little motor. It is 1720 rpm and 1 hp. But, it can be wired to both 1720 rpm and 3445 rpm. It is rated at 5/8 hp @ 1720 and 1 hp @ 3445. It will be powered by a Chinese VFD, rated from 1 Hz to a gazillion or so Hz.

How should the motor be wired in order to achieve the best combination of rpm and torque. As a 4 pole 1720 or 2 pole 3445? The VFD can be programed to accommodate either. As you may have guessed, I am a step or two beyond by understanding of these things.

Bill
 

Barry

Diamond Level Sponsor
Bill,

The 4-pole / 1720 RPM and 2-pole / 3445 RPM 3-phase motor combinations are almost certainly based on 60 Hz power.

If so, the conservative approach would be to select the combination that most closely matches the RPM of the fixed speed single-phase motor that is being replaced.

Cranking the controller frequency up to 120 Hz would probably make the 4-pole setup turn 3400 RPM, but I suspect the motor would overheat unless the load on the motor or the controller output current was reduced. Getting a quart out of a pint pot is rough on the pot.
 
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RootesRacer

Donation Time
If you wire it for the 3445 RPM config, running it off the VFD will give you a wider running range while keeping the drive frequency near the 60hz nominal drive freq.
If you only plan on 1720RPM, then wire it as such, but being able to set the volume control to 11 some times is nice.
The VFD would have left you run the 1720 RPM config at 120hz to get to the same 3445 RPM speed but the efficiency would be a bit lower since the magnetics would be running outside its normal phase shift at the frequency with more parasitic/hysteretic core losses.
 

Bill Blue

Platinum Level Sponsor
So it seems my logical choices are to wire 3445 with pulley change to give 50% reduction to limit spindle speed to stock 1200 rpm.
Or, wire 1720, with the pulley change and increase Hz to 120 to give 3445 achieve stock spindle speed of 1200. The installation difference being how three wires are connected. A change that requires about 5 minutes. Heat, I'm concerned about. Efficiency, not so much. I know, one follows the other.

Sounds like Science Fair time.
 

SoCal'beaming

Donation Time
Interesting discussion ... more so if I understood it completely, though I relate to this analogy Barry gave "Getting a quart out of a pint pot is rough on the pot" o_O
 

RootesRacer

Donation Time
Bill, how many VA are you planning for the VFD?
I have a few brand new 750VA/1HP Lenze drives as well as a 2.2KVA Lenze. You could barter/trade me for if you havnt bought the chineseum one.
 

Bill Blue

Platinum Level Sponsor
Not sure, my knowledge of Chinese is non existent. Lots of number, but no comprendo. Doing some rough measurement and maths (after all, this is British car site) my guess is 1720 rpm. The owners manual gives two motor sizes, 1 and 1 1/2 hp. Sounds simple enough, except for the hand stamping on the motor data plate. 1 hp seems to be most likely.

When I saw the new motor was 1 hp @ 1720 and only $102 including shipping, I thought I had struck gold.

Bill
 

Barry

Diamond Level Sponsor
Can't help with Chinese writing.

A 1 HP 3-phase motor and a 2.2 KW (about 3 HP) 3-phase VFD for less than $200 delivered is pretty amazing.
 

RootesRacer

Donation Time
I have been thinking of replacing my mill motor with an AC servo motor, which is like a closed loop stepper motor that has a very wide operating speed range. Where can you get a 1hp 3 phase motor for $109?
 

Bill Blue

Platinum Level Sponsor
Ebay. This unit was industrial surplus. For numerous reasons, factories end with cats and dogs they no longer have any use for, so they sell the whole shebang to someone who disposes of it a piece at a time. So I don't fault the seller. His "man" probably opened the box far enough to determine it really did contain a three phase motor and did not pursue it much beyond that. He probably knows less about them than I do. As a group, I think they are very honest, but they deal with stuff about which they know little. So there is always a chance you end up with something a bit strange.

They often deal in very small quantities, so if you see a good deal, better snap it up before Barry gets it.

Bill
 

Bill Blue

Platinum Level Sponsor
SUPPLIES!! (Punch line to an old, really bad joke)
An unheralded feature of this motor is a permanently attached shaft key. Non standard size attached key, too be exact. Maybe its metric, don't know. Anyway, it is bigger than the pulley keyway and I cannot move it. So I clamped the motor shaft in the mill vise, took 5 thou off the top and 21 thou off each side. Fits the old pulley like it was modified for the job.

Bill
 

Barry

Diamond Level Sponsor
Bill,

How about an update on the VFD for your Enco lathe.

Did it work? Was it worth the hassle?
 

Bill Blue

Platinum Level Sponsor
Not a whole lot to update. Got involved with the Alpine to get it road ready for the Invasion. Then the steering wheel. Just now getting back to the lathe. I spent a lot of time finding appropriate parts and deciding just what should go where. It should be complete in a day or so. I have a decent sized job lined up for it, I'll let you know how it performs.

Bill
 

Bill Blue

Platinum Level Sponsor
Early returns are in.

I wired the motor as a four pole, thinking that would give me more power. A 5/8 hp @ 1725 should develop 1 1/4 hp @ 3455 instead of the 1 hp @ when wired as a two pole. I think.

I am running the lathe in the slowest non-backgear pulleys, which is 300 rpm, using the factory motor. The VFD is flexible enough that I can thread (1/4-28) at 20 Hz and it will run 600 rpm @ 120 Hz, This is faster than I ran the lathe with the stock motor. In order to go faster, it was necessary to switch the belt to the high speed motor pulley, which is a gen you wine PAIN IN THE ASS. So it appears I can cover most of my operating speeds with the turn of a dial. I know that it will be necessary to engage backgears to thread larger sizes. I have no idea what the performance will be at lower frequency.

Right now, I'm getting used to the controls. Twenty years of starting and stopping the lathe with a hand lever that is conveniently located on the saddle is way different than push buttons located on the back of the lathe. I have the lathe wired so the old start/stop handle now turns the VFD on and off, not the motor. Can't do that. When stopping, power has to be cut to the VFD, not the motor. Cutting power to the motor will fry the VFD.

Also, soft starts are weird, but nice.

Bill
 

Bill Blue

Platinum Level Sponsor
I spent a good portion of yesterday using the lathe, threading rod to 1/4-28. Ran the motor at 16 Hz, After an hour of constant stopping, starting and running, the motor was barely warm to the touch. Maybe 10 degrees above ambient.

I'm getting to like the set up a lot. It allows the operator to do things he would never otherwise consider. Miss your thread dial engage point? No problem. Hit fwd/rev. The lathe comes a rather quick but gentle stop and restarts in reverse in a quick, but gentle fashion. Go back to a convenient point, hit fwd/rev and try again. I would never do this with the old motor as all starts were rather violent and the lathe has a threaded spindle. Don't want that thirty pound chuck on my feet.

Now all I have to do is reprogram myself in order to properly operate it.

Bill
 

Barry

Diamond Level Sponsor
Late 19th century mechanical technology combined with early 21st century electronics. Who woulda thunk it?
 

Bill Blue

Platinum Level Sponsor
Extend use report. I love it! Especially the soft starts. I seldom have to change belt pulleys, had a job or three that required back gears. But the cheap Ebay VFD is a users dream. Buy one that is oversized for the job and enjoy. It will still be low priced. The amazing thing is they are preset from the factory and are usable out of the box with only one or two simple control inputs. The instructions include directions to change settings for everything, but I cannot fault its operation with the default settings.

With all this convenience, I'm sure the motor gets abused, so I often hand check the temperature. Never has gotten hot. Being a hobby application, I do not push the machine for productivity. No blue chips allowed!

Bill
 
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