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Tom S
05-13-2010, 10:41 AM
A quick question about VFD's. I have a Logan 821, which uses a 1/2hp single-phase motor. I have been keeping my eyes open for a VFD to upgrade the motor to a 3-phase unit, and have found a deal on one. My question is: Should I replace my 1/2hp single-phase motor with a 1/2hp three-phase motor, or with a larger three-phase motor? I'm just thinking that when the motor is running at lower rpms the torque will be reduced and may make the lathe underpowered. And could someone please confirm that I will need a inverter-duty motor to have variable rpms?

-Tom

RTPBurnsville
05-13-2010, 11:03 AM
Hi,

I recently replaced the 1/2hp motor on my 9 inch southbend with a 3/4hp three phase motor and have been very pleased. The lathe is now very quiet and the variable speed is way cool. There were only a couple dollars difference in price between 1/2 and 3/4hp motors so that was a no-brainer. There are some losses with VFD so that was my main reason for picking a slightly larger motor.

For a drive I selected the Automationdirect GS2 drive (1hp, 220v model). I liked the ability to just add external resistors for breaking. Also their manual was easy to understand and the drive had good reviews from other users.

The motor is the rolled frame version also from Automation. The main difference between invert type motors and non is the quality of insulation used on the windings. For homeshop use I rolled the dice and went cheap. I also purchased the adjustable mount but ended up not using it as things did not align easily with it on my Southbend.

Robert

lakeside53
05-13-2010, 11:04 AM
You do not need an inverter rated motor.

You will need a larger motor IF you need 1/2 hp at low rpm, AND you do not keep the existing pulley system in place. At 10hz, you'd have about 1/6th HP, so you'd need a 3hp motor...

Realistically, if you keep the existing pulleys/back gear or whatever, a 3/4 to 1hp motor will work fine. Only "change down" if you need more torque.

If you intend to run the motor at low rpm, you'll need an additional/replacement fan - a "muffin" 4 inch computer fan suffices.

MaxHeadRoom
05-13-2010, 11:23 AM
I will usually fit an inductor between VFD and motor on systems that use the original non-vector motor.
See this tech sheet from Baldor.
http://net.grundfos.com/doc/webnet/boosterpaq/BoosterpaQ%20CD/Misc%20Tech/Inverted%20Fed%20Motors%20-%20Baldor.pdf
Max.

Tom S
05-13-2010, 11:39 AM
The main reason I am asking about if a 1/2hp model will suffice is because I have the opportunity to buy a used 1/2hp Allen-Bradly drive for $60, while the next size up is a 2hp Toshiba for $175. I guess if I keep the drive system intact I can always gear down and keep the rpm's up at the motor.

-Tom

lakeside53
05-13-2010, 11:49 AM
Output inductors? I don't bother, and have seen hundreds of commercial installations where VFD's are connected to "non-inverter" rated motors with no problems.

They are of course technically correct, and the caution of keeping the carrier frequency low is good, but wonder how much of this was written to promote Baldor's inverter-rated motors?

For a HSM.. a surplus 1hp motor is going to cost a lot less than the series inductors.

J. R. Williams
05-13-2010, 11:49 AM
You will have to use a larger drive unit when operating on single phase. Typically use a 3/4 hp drive on a 1/2 hp motor when on single phase unless the drive has a single phase rating. Check the drive specs carefully.

JRW

lakeside53
05-13-2010, 11:51 AM
The main reason I am asking about if a 1/2hp model will suffice is because I have the opportunity to buy a used 1/2hp Allen-Bradly drive for $60, while the next size up is a 2hp Toshiba for $175. I guess if I keep the drive system intact I can always gear down and keep the rpm's up at the motor.

-Tom


You might be much happier with a brand new $114 Teco - 115 input , 3 phase 230 out, 1hp.

Tom S
05-13-2010, 12:03 PM
That might be the better option. Then there is no question if there is enough power in the drive, and if I find the motor can't cut it I can swap it for a 3/4hp.

-Tom

RobbieKnobbie
05-13-2010, 12:28 PM
If you're used to 1/2 HP from that lathe then you'll be delighted with a 3/4 horse motor. The inverter is not there to replace your step pulley, just to add some flexability. If you need low speed and lots of torque (taking monster cuts on very large diameter material?) then you'd still have to gear down with the pulleys and tweak your speed in with the VFD. If you're looking for low speed with little torque (tapping, etc) then by all means leave the pulleys alone and just turn down the drive. My point is that the physics of mechanically gearing up/down don't go away just because you put a control on your motor.

Teco is said to be a fine, inexpensive drive... Automation Direct has some as well. I've installed several of the AD's and am very happy with them. Either way you do not need an inverter duty motor unless you're running your lathe hard for three shifts a day.

Pretty much all the manufacturers offer drives designed to run on single phase input - these do not have to be derated and can run any 3ph motor up to the rated capacity of the drive.

I have a little experience with AB drives and I wouldn't go with them if it were my first install. Not that they aren't fine drives, but they're marketed to the industrial crowd and their documentation is written accordingly.

(edited for stupidity)

metalmagpie
05-13-2010, 03:12 PM
I will usually fit an inductor between VFD and motor

Max, do you just use the primary of an old transformer or what? Actually, I guess you'd need 3 matched transformers. It is usually really hard to find 3-phase inductors, and spendy. I would love to do this. Maybe 3 transformers from old computer UPS boxes? Shouldn't be too hard to find a matching pile of those ..

metalmagpie

Doc Nickel
05-13-2010, 03:48 PM
My Logan came with a (presumably retrofitted) 3/4HP single phase when I first got it. It was adequate for a while, but definitely underpowered if I tried to push it.

I swapped that for a 1-1/2HP single, which really appeared to make little difference- it was still a bit underpowered for some things. In my turret lathe video (http://www.youtube.com/watch?v=rqclIfMKVS8), you can hear it slow down during the knurling step, and really, I couldn't even push the drills all that hard or it'd bog too.

I finally swapped that for a 2HP 3-phase, and also stepped up from 1725 to 3450. I powered this with an AD GS2 and a new control box that laid out all the usual stuff- start/stop, speed dial and a reverse switch.

Now, instead of using the top speed on the Logan- which originally gave me about 600 rpm, max- I now use the lowest non-backgear speed, which, with the faster motor, gives me about the same 600 rpm, but a pile more torque.

I can no longer stall the thing even if I try. I took a .200 deep cut at .009" in aluminum and it hardly noticed.

Unless every last penny was a major issue, I'd suggest at least going up to a full 1HP motor and 1HP controller. As noted, you'll keep more HP at the lower speeds so you'll have to do less belt-swapping.

And no one, in the history of the world, has ever said "Darn, my lathe just has too much power!" :D

Doc.

Bguns
05-13-2010, 04:05 PM
INVERTOR GRADE MOTORS ARE NOT NEEDED FOR LESS THAN 24/7 DUTY.

LONG TERM OPERATION AT REDUCED/INCREASED MOTOR SPEEDS, MIGHT REQUIRE AN ADD ON COOLING FAN FOR MOTOR.

DERATING OF SINGLE PHASE INPUT RATED VFD's NOT NEEDED.

SOME 3 PHASE INPUT VFD's WILL NOT OPERATE (DERATED) WITH SINGLE PHASE INPUT ONLY. SOME WILL.

MANY VFD's AVAILABLE UP TO 2 HP, WITH SINGLE PHASE ONLY INPUT.

THE STANDARD MACHINE BELTING AND GEARS, HANDLE ALL TORQUE MULTIPLICATION REQUIREMENTS.

MANY SMALL (< ~1.5HP) VFD's, ARE MADE FOR 110 INPUT VOLTAGE, AND PROVIDE 220 V 3 PHASE OUT.

MOTOR BEARING LIFE WILL NOT BE AFFECTED ON 220 VOLT VFD's.

INDUCTORS ARE JUST NOT NEEDED IN A HOME SHOP.

VFD'S OUTPUT SHOULD BE WIRED DIRECTLY TO MOTOR INPUT, NO DISCONNECT OR SWITCHES. VFD IS CONTROLLED BY LOW VOLTAGE WIRING.

VFD's PROVIDE MOTOR PROTECTION STANDARD.

VFD's ALLOW MOTOR SPEED TO BE RUN UP 100% ABOVE NORMAL MOTOR SPEED. BEARINGS, VIBRATION, AND OILING, MUST BE CONSIDERED.

VFD"S ALLOW MOTOR SPEED TO BE RUN DOWN TO ~ 25% OF NORMAL MOTOR SPEED AND STILL PROVIDE PLENTY OF TORQUE.

BRAKING RESISTORS MIGHT NOT BE A GOOD IDEA WITH THREAD MOUNTED CHUCKS.

VFD's ALLOW FOR INSTANT OR RAMP DELAYED REVERSE. VERY HANDY FOR TAPPING. NOT SO HANDY WITH A THREAD MOUNT CHUCK.

VFD"s DO CAUSE MOTORS TO EMIT A HIGH PITCHED WHINE.

ADJUSTING VFD CARRIER FREQUENCY UP WILL HELP. DO NOT ADJUST HIGHER THAN NEEDED TO REDUCE WHINE.

VFD's ARE THE BEST THING INVENTED SINCE SLICED BREAD.

LESS (NOT NONE, HOWEVER) BELT/GEAR CHANGES.

VFD's ARE NOT IDEAL FOR MULTIPLE MOTOR APPLICATIONS. THEY ARE CHEAP ENOUGH TO PLACE MULTIPLE VFD's ON MULTI MOTORED MACHINES THOUGH.

EDIT: 2 HP ON A 9 INCH SOUTHBEND/ATLAS WILL BREAK THINGS. :)

Black_Moons
05-13-2010, 04:30 PM
^-- Shouting Makes Me More Correct Then Other People And Makes Everything I Type Easyer To Read If The Reader Is Nearly Blind.
Wow, He had to actualy go back and edit that to all caps too, because the forum automaticly decapatlises all caps posts.

Tom S
05-13-2010, 04:30 PM
Thanks for all the info. Lots to base my purchase on.

Doc, are you sure that your lathe was not modified before you purchased it? My Logan's top speed is in the 1200 range if I remember correctly, and it is bone stock as far as drive components.

I think I will look into the 1hp. I would love to be able to run without the backgear, and the 1hp may have enough torque to allow me to do that. I don't mind switching speeds on the step pully.

-Tom

Tom S
05-13-2010, 04:32 PM
^-- Shouting Makes Me More Correct Then Other People And Makes Everything I Type Easyer To Read If The Reader Is Nearly Blind.
Wow, How did he even do that, the forum AUTO

LOL. It was hard not to say anything. Nothing personal.

MaxHeadRoom
05-13-2010, 04:35 PM
Max, do you just use the primary of an old transformer or what?

I either get them from the VFD supplier, or any motor supplier that also supplies vector motors, the transformer manufacturers also supply them such as Hammond.
I don't usually use anything special for the motor wiring, usually single conductor stranded, TEW/MTW, but make sure the three conductors are twisted together if running in liguid seal flex etc.
Make sure you take a ground to the VFD and continue on to the motor frame, don't twist the ground with the other three.
I run 4 pole motors up to 120hz, 2 pole motors, not much over 60hz.
Max.

Forrest Addy
05-13-2010, 04:35 PM
Bguns has emmitted gold onto the computer screen. I agree with and endorse all his Commandments except the very last: a SB/Atlas grade lathe will take 2 HP no sweat at full load. The belt will slip before it causas damage. However be careful when using the back gear. If the belt snug a full 2 HP cut is a definite overload in low and mid pulley/back gear. That's a 10" lathe. A li'ler guy like a 9" breaks easier.

Erik Brewster
05-13-2010, 05:05 PM
On my previous 12" logan, I changed the original 3/4 (I think) for a 3 Hp with vfd. I loved it. I could bog that motor down, too, but it was very usable. I can't imagine doing less than 3 Hp on a lathe now, given torque derating at low speed. I can understand varying levels of financial commitment, however.

I don't think you will ever have too much power. I can also tell you that the vfd variable speed is even nicer than you imagine :)

Doc Nickel
05-13-2010, 08:09 PM
Doc, are you sure that your lathe was not modified before you purchased it? My Logan's top speed is in the 1200 range if I remember correctly, and it is bone stock as far as drive components.

-I'm certain it was. The fellow I got the lathe from had installed the then-new Marathon 3/4HP motor. I didn't ask at the time, but I suspect because the lathe came with a 3-phase motor, since it was originally a production turret machine.

I don't know how or why the fellow chose that particular drive pulley. Whether he chose it at random because it was what he had on hand that day, or because it was the same size as was on the motor he removed and he didn't know or consider that it was 3450, or perhaps he specifically decided that 600 rpm was plenty.

Sadly, he's beyond my ability to ask now, so I can only guess. But yes, a while back as I was planning a re-remotoring and/or pulley swap, several people told me theirs had a 1200 rpm top end.

So does mine, now. :D

Doc.

lakeside53
05-13-2010, 09:29 PM
For those interested in output fliters, here's a typical 3hp unit (at 240 volts)

http://www.galco.com/scripts/cgiip.exe/WA/WCat/itemdtl.r?listtype=Catalog&pnum=RL-01202-MTE


However, this is what Phase Perfect has to say about filtering :


The output voltage from a VFD is not sinusoidal, but rather a series of pulses which have average values that are sine waves. The switches that control these pulses have to make their on/off transitions very rapidly (in about 0.2 microsecond) for the VFD to operate efficiently. The high frequency components of these pulses travel from the VFD to the motor through the connecting wires, which become an electrical transmission line. Transmission line effects are normally not a problem at 60 Hz to the average user because the wavelength of a 60 Hz signal is about 2200 miles (assuming the signal travels at 0.8 x the speed of light in the wires). However, at 5 MHz the wavelength drops to about 180 feet and the effects become important. The electrical impedance of the transmission line is unpredictable but typically has values between a few tens of ohms to a few hundred ohms. On the other hand, the impedance of the motor and the VFD is usually just a few ohms. This mismatch between the line impedance and the impedance of the terminations at the motor and the drive causes standing wave patterns to be set up in the line with resultant voltages that can be much larger than the voltage at the drive output. These standing-wave voltages can damage the wiring, the motor and the drive. If the distance between the VFD and the motor is short (less that 10 feet), there shouldn't be any problem. As the distance approaches 50 feet or more, most VFD manufacturers recommend that output line filters be used on each of the output leads.
In their simplest form these filters consist of an inductor in series with each output line with a capacitor connected to the second terminal of each inductor. The other terminal of each capacitor is connected to a common point. This filtering does not make the output voltages sinusoidal, and so even with filtering, residual harmonics may have some impact on the wire and motor in installations where the motor and drive are far apart At distances of 200 feet or more, as would be typical for a deep-well submersible pump, output line filters are a necessity and will add to the cost of the drive installation.

J Tiers
05-13-2010, 10:53 PM
The info from BGUNS is good...... I deal with VFDs nearly every day in a consulting biz and I agree with essentially all of his info.

As for the phase perfect stuff..... there is some truth to it. But the added inductor with teh capacitor is not a perfect solution..... That makes a resonant circuit, and depending on values, it may actually make the situation WORSE than with no filter at all.

The best is very likely a somewhat lossy inductor..... Forrest once suggested "pipe slice core" inductors and that is far from a silly suggestion... the losses reduce the "Q" and thus the voltages. The solid iron core is lossy. otherwise some form of damper might be needed, which would be lossy anyhow.

Older motors, if the insulation is not damaged, may have BETTER insulation phase-to-phase than new motors. They were made back when time was taken to set the insulation correctly.... and they were often double-dipped in varnish.

The wire varnish in older motors isn't as good as new types, but that tends to be less critical. Most varnish is good for at least 50 to 100V, so assuming the first 10 turns get the most transient voltage, that's still 500 to 1000 V of transient-resisting wire insulation, on a 240V motor.

Just about none of the typical VFD issues ARE issues at 240V.

Forrest Addy
05-13-2010, 11:37 PM
For those who love to sweat details, those who jump at the lightest technical shadows, and for those casually curious here's my recipe for series inductors for gelding line transients from a VFD.

Find a hunk of iron pipe; even cast iron will work - possibly better. Size the pipe about 1 1/2 times the cube root of the motor HP and use that number to select the nearest size schedule 40 iron pipe. Cut 3 pieces about 1/2 as long as the OD of the pipe. Deburr and radius the corners. Wrap the pipe wall in electrical tape, half lapping it.

OK you got the core. Now for the inductor winding: Wind about 6 to 10 turns of the VFD output conductor toroid fashion around the pipe wall. Wire each inductor between the VFD output and the motor. At the motor's J-box, star connect the motor leads with three ceramic disk caps 0.01 MFD and ground the center of the star. If the motor acts funny use smaller caps maybe 0.002 MFD.

Scientific aint it? The object is a dirty lossy inductor that blots up HF transients without seriously affecting the back EMF wave form.

99% of the time you need no such refinements. If the VFD hash interferes with Rush or NBR on the radio run the wiring through metal conduit and make sure all the grounding is up to snuff. If you still have problems enclose the VFD in a NEMA 12 enclosure and add an LC pi filter in the line input.

Richard-TX
05-14-2010, 02:04 AM
I agree with Bguns with one exception. 3 hp is the now current limits, not 2hp.

JTiers is also correct. Recent tests have shown that older motors meet or exceed inverter ratings and for all the reasons he gave.

Studies have shown that legacy 230 volt motors usually have a longer MTBF when powered by a VFD.

I have a problem with Phase Perfect. Their white paper has a couple of statements in it that are plainly wrong. To me that places everything they say under a dark cloud of suspicion. I hate it when I have to question everything a manufacture says.

Guess how many of the new South Bend lathes come equipped with a VFD from the factory?

If you guessed "All of them" you would be right.

VFDs are getting better and better all the time. Soon they will be standard on all residential air handlers, pool pumps, etc.

Tom S
05-14-2010, 07:20 AM
Thanks for all the info gents. I'll be keeping my eyes open for a 3/4 or 1 hp 3-phase motor an appropriate VFD.

-Tom

Doc Nickel
05-14-2010, 08:06 AM
VFDs are getting better and better all the time. Soon they will be standard on all residential air handlers, pool pumps, etc.

-It took me a while to warm to the idea of 3-phase and a VFD, largely because I don't have a terribly firm grasp on electrical components to start with.

But once I had a chance to use one, and take advantage of it's capabilities, I was hooked. Now, seven of my machines are 3-phase, some on a rotary converter, most on individual VFDs- and I'm working on either aquiring or converting still more.

Apart from the cost (a bit over that of a simple single-phase motor) and the additional complexity (more wiring, plus control conversion, plus some programming) there's very little drawback.

I imagine we'll be seeing more and more of that kind of setup on commercial products, like treadmills and the like- and hopefully they'll be as easy to salvage hardware from as the current ones. :D

Doc.

RB211
05-14-2010, 01:14 PM
I imagine we'll be seeing more and more of that kind of setup on commercial products, like treadmills and the like- and hopefully they'll be as easy to salvage hardware from as the current ones. :D

Doc.

At my gym, every piece of cardio equipment that has an electric motor I'd wager does in fact have a vfd.

MaxHeadRoom
05-14-2010, 02:55 PM
At my gym, every piece of cardio equipment that has an electric motor I'd wager does in fact have a vfd.

Sure they'r not DC variable speed? ;)
Max.

Doc Nickel
05-14-2010, 03:26 PM
Sure they'r not DC variable speed?

-All the "home" treadmills I've taken apart have been cheap DC motors. But I took apart three heavy "industrial" treadmills from a local fitness place, and two of them had an oddball open-frame motor that the tags said were "115V 3-phase", and had six conductor cables.

The third, though, did have a monster 4HP (!) 220v DC motor, that I still wish I could find a speed controller for.

Doc.

MaxHeadRoom
05-14-2010, 04:01 PM
The third, though, did have a monster 4HP (!) 220v DC motor, that I still wish I could find a speed controller for.

Doc.

Ebay 220602357780 ?
Max.

Bguns
05-15-2010, 04:06 AM
Gee, expecting major flame war...

Capitals only, usually mean fun... Should have just numbered the individual lines.. Military training, called Bullet Statements on Soldier evaluation reports... Short, to the point, minus BS...

I just had a 85 year old customer in, He does not see so good... :)

I have actually installed 3 VFD's of mixed breeds. Leeson, AC Tech, Teco.

They work, and well.

I still think a SB 9/Atlas with a Serpentine or V belt drive, will bust a gut with 2 hp. :)

The stock 1 inch wide flat belt will provide protection, but also will not transmit the full 2 hp... Even J head step pulley Bridgeports, use fractional hp rated belts.

My 1937 or so, SB already has had cast iron back gear brazed up ...

My electrical experience is pretty basic, but I did stay in a Ham Shack Inn last night.... de WL7WW

lakeside53
05-15-2010, 11:09 AM
The lathe can work fine with a 2hp motor... You simply program in reasonable current limits to stop the user from inadvertently making the motor develop more than say 1hp. The advantage of a larger motor is more power at reduced rpm - less belt or gear changing.

If you don't program in lower limits, a tool crash may well break something.

It's common for varibale speed lathes to have quite large motors to compensate for low power at low rpm.

ulav8r
05-16-2010, 05:31 PM
At least one high priced treadmill has a VFD adn 3 phase motor. It is advertised as a 5 hp motor. According to the lab report the motor will develop 5 hp at 380 volts and 120htz. The vfd supplied has 120V input and puts out 7 amps, in other words it is a 1 hp VFD and the treadmill will not produce more even though the motor could produce more power with the right VFD and power supply. I have one of the motors and a 2 hp LG VFD thats will be installed on my heavy 10 if I ever have a shop and power supply that can handle it.