Variable Frequency Drive

[shenion]

So, the motor on my lathe is shot. Probably 1940's vintage. It shakes like crazy. As the motor hangs off the back, I bet the shaft got hit during transport and bent. Looking closer, it has cloth-covered wires that would need to be replaced and probably could use new bearings.

So, off to ebay to look for a replacement. Either the motors are beat up, wrong speed, shipping is obscene or everybody and their brother has a lathe/drill/saw that needs the same size motor and the price is way more than it is worth.

However, there are dozens of 3-phase motors, brand new with no bids.

So, I decided to look at VFD controllers. Dozens of 460V 3-Phase in/out, dead/untested ones and units missing parts.

I stumbled on a unused, Toshiba 110V single-phase in to 208V 3-phase VFD. Only 1/2 HP so not a big interest (seems everyone wants 2HP and up.) Did last second bid and picked it up for $27. Will do 0.5 to 200Hz and has LED display/keypad:

Next, bid on brand-new, 1HP 3-phase, 1100RPM motor. Only bidder,and pick up for $25 + $14 shipping. So, motor + VFD, both new all for less than $100. A decent BB motor would have cost me that.

Got the motor yesterday, and fitied it on the lathe:

Hopefully, the VFD will come today. It does not have a reversing switch on the panel and I don't want it on the lathe. So I will make a remote control panel with start/stop and direction controls.

Will post progress as I go along.

 

[aero]

These drives are becoming very popular. You get great speed control, modern electric safety on an old machine and can use 3 phase motors that no one wants. I have one on my boxford.

 

[dannyweld]

hi shenion, just noticed your address, GA, is that georgia. i spent a summer in roswell, north of atlanta. my family has got an engineering works (cnc lathe) in ballpark (i think, old indian place).

 

[AndyP]

How are you going to run a 1HP motor thru a 1/2 HP inverter?

 

[shenion]

Yes, that is Georgia.

The lathe currently has a 1/3HP motor. So 1/2HP will be fine. I suspect I will have to adjust the ramp-up speed to use the 1HP to prevent over-current trip, but once going, it should work fine.

 

[shenion]

Received the VFD today:

I made the upper panel to use (came from old line printer so had lighted stop/run buttons.) There is also a forward/reverse switch.

Oh, here's a closeup of the welding of the panel bracket:

Lincold Fleetweld 47, 3/32 6013. Just grabbed a rod, flicked on Airco at approximate setting, 2 zaps and done.

The VFD has been temporarily bolted to the front leg of the lathe. Will be put in an enclosure with a fan later. Just wanted to see how it works

Took a bit of fiddling to get it going. It was set up for no panel control or remote (must have been used on serial.)

Once I got it to start, it tripped just as it was getting to full speed. I had expected that. Dug through the many dozen settings and found the PWM frequency. Set it lower as this is not a motor designed for a PWM drive (the VFD accounts for this but defaults to high-freq PWM for the special Toshiba motors.)

Once set up, it spins up the lathe nice and slowly. Wow, what a difference. The old motor caused the lathe to actually walk around (rotor way off balance.). There was also a lot of hum.

Now smooth an quiet. Just a bit of whine from the motor that is not objectionable. Looks like I'll get about 40-80 Hz speed; any lower and the motor just stops. May go higher but that is the default max programmed in. That is enough to avoid having to change to the next pulley at times. Motor is 1140 RPM so lathe will be slower. Should be fine.

 

[shenion]

Ok, this is cool

I was getting over-current trip on stopping. Very odd as the frequency would ramp down to 55hz and just stay there, then it would apply the brake and trip.

Messed with dozens of parameters. Some seemed to help, most had no effect.

Finally did something I should have done from the start: reset to factory defaults. It was removed from new equipment (something about a demo setup.) Who knows what was changed.

Now it trips with over current all the time. Checked and it set the motor current to 1.2 amps. Upped it to 2.4 and now everything works. Odd as I had set the current before. The motor is rated at 4.0 amps, I want it less to limit HP.

Played with it. I have the speed control going from 40 to 90 Hz. That gives me 740 RPM to 1740 RPM. Before anything below 50hz would cause over current. The old motor was 1750RPM so I can match the speed if needed. I can change the speed while running too.

Seemed to be stable at almost any frequency. Get a lot of whine below 40hz and have tried it up to 100hz (VFD will go to 200Hz.)

If I set the freq to 40Hz,use the smallest drive pulley and engage the back gear, the chuck turns about once a second.

It ramps up to speed in about 4 seconds. It will stop in about 3 seconds (set to 2.5.) Could stop faster but don't want to spin off the chuck.

The lathe used to have a double motor pulley and countershaft pulley. The coutershaft pulley has a worn hub and the double motor one is missing. With this I can match the two pulley spindle speeds.

 

[Luke]

Parameterising drives with a laptop is far far easier than using an OP all day, that's for sure!

 

[shenion]

Finished it up tonight:

No longer such a fire hazard Enclosure is an 8x8x6" junction box. I cut a fan into the bottom.

Tested it down to 5Hz tonight. Got about 3 RPM on lathe

I have the dial on the front set to run from 20 to 100Hz. That gives me 5:1 adjustable along with the 4 pulley speeds and back gear.

More info on my Craftsman Lathe Pages.

 

[shenion]

Have a video of lathe running at 2.4Hz. That gives about 1 RPM. Worked at 0.5Hz for about 1/5th RPM.

It could be used as a welding positioner.

The video is on the bottom of one of my lathe pages here.

It works ok, but it does overheat on heavy turning. I just fixed a larger countershaft pulley so it can run the motor at a higher speed with less current.