What about 2hp 240v 3 phase vs 2hp DC treadmill motor for lathe or mill?

pdentrem

pdentrem

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At work, everything is 3 phase, 240 volt and up. At home my 2 hp, 240 volt single phase motor on the lathe I am going to replace. The question is - advantage or disadvantage between a VFD and 2 hp 3 phase motor verses a 2 hp treadmill DC motor?
I am familiar with setting up VFDs and DC motors but never did one side by side to compare.
Pierre
 
pdentrem said:
At work, everything is 3 phase, 240 volt and up. At home my 2 hp, 240 volt single phase motor on the lathe I am going to replace. The question is - advantage or disadvantage between a VFD and 2 hp 3 phase motor verses a 2 hp treadmill DC motor?
I am familiar with setting up VFDs and DC motors but never did one side by side to compare.
Pierre
Click to expand...

The horsepower rating of an electric motor is based on the internal temperature of the armature. The 2hp existing motor is most likely a continuous duty rating, meaning you can pull max hp all day long. The treadmill motor has a short term rating. It may produce 2hp, just before it goes up in smoke in a few minutes.
I use treadmill motors/controllers, but not for anything requiring serious power like a machine tool.
 
Massive difference between a 2 Hp 3 phase motor that is designed for continous use and a treadmill motor that is 1/4 of the size physically and yet they have given it a mythical rating of 2 HP. NOTE: That is 2 Hp peak "developed" Horsepower, not continuous, nor is it that it can start under a rated load of 2 Hp. That treadmill that it came off of, was designed to be started with the user not stepping on the belt. Those motors are actually way less in true HP and when they are actually developing full rated HP, is just before they are about to fail in a spectacular show of "letting the magic smoke out"

Now on top of that if you are planning on running the lathe at low RPM's you need to further examine the HP of the motors. Right now you have a 2 HP single phase motor that is running at one consistent speed, probably 1725 RPM, and you get your speed changes by either shifting belts or gears. Belts and gears multiply or divide the speed and when they divide the speed, they increase the torque, but say you change to a 2 HP 3 Phase motor and power it with a VFD. Now as the speed drops, so does the HP output of the motor and the torque also reduces. It is generally accepted that in changing a motor from single to 3 phase that you can use a bit smaller of a motor to get the same amount of work done, IE a 3 HP 3 Phase wood working planer requires a 5 HP single phase motor, or a 5 Hp 3 phase air compressor requires a 7-1/2 Hp single phase motor to operate, but if we VFD that three phase motor then we have to go the other way around so that 2 HP 1 phase lathe will want a 3 or larger HP 3 phase motor so that it can maintain torque at low speeds.

Also it is best to maintain the belts or gears in the machine and use the VFD to vary the speed within the ranges of the belt/gear changes to maximize output of the motor. So now we have a lathe that say had 12 speeds, so we now have 12 ranges of speeds from about 30% or less under to 200% faster per range assuming that the motor is inverter rated and you operate the VFD up to 120Hz.

Furthermore when a motor is run at very slow RPMs as can happen with a VFD on a 3 phase motor, a method must be supplied to supplement the cooling of the windings, thus a seperately powered fan as usually attached to the end of the motor shroud that will keep constant speed and constant cooling of the motor, regardless of the RPM it is turning.

Walter
 
I like a VFD and a VFD rated motor better. Many dc motors will have brushes. Just something else to go bad. Plus for a machine that needs as much as 2hp to run. A good vfd and motor with 2hp will be a good match for power. It may cost a bit more to go the vfd route I think you get what you pay for.
 
All good input above. I have wrestled with the variable speed option as well and I have a few observations:
1) I have had a 100v DC motor on my cheapo drill press for about 20 years and it works OK to drop the spindle speed down to speeds more appropriate for metal work. I think I set the pulleys at the lowest speed when I put the drive on and I've never needed to change it to do what I want to do. I do use the variable speed a lot as I change drill sizes, but not the step pulley. Haven't worn out a set of brushes yet.
2) It's been a long time since I took physical science, but, as I recall, the formula for horsepower is HP=RPM X TORQUE/5252. So, a 2 HP motor develops 2 horse power at some RPM when it's making some amount of torque. In the case of a fixed speed AC motor that fixed speed is the RPM in the equation. If you start to manipulate the RPM with some outside device like VFD or a DC controller the horse power the motor develops will drop accordingly. The torque a motor develops is directly related to the current that the motor is absorbing. When you drop the effective voltage to the motor, the current drops and the torque and HP go along with it. Some controllers have a "torque control" setting which may help to mask some of the effects of the above, but the fundamental issues still exist. I'm not sure exactly what happens when you overdrive a motor with, say, a frequency higher than the nominal rated frequency. It should make more power, but It's probably not directly proportional and may have some other detrimental effects (heat). Most of you probably melted a small DC motor by over powering it with high voltage so that's the direction I'd expect things to go. Goes fast as hell for a moment and then all the smoke leaks out.
3) While the infinitely variable speed option sounds like a cool thing, I don't find myself changing the step pulleys on my mill very often and the three speeds on my lathe seem to be adequate. Keep in mind, I'm just making hobby parts and I'm not trying to get 110% out of any of my machines. If you really want to maximize the efficiency of your operation, the variable speed may be a good option, but for less intense use, it may just be an added expense and another board to go bad.
 
I was already to go with a 3 phase and VFD from my local motor shop when a friend mentioned he had a 240 volt treadmill motor and the threadmill it came from. Likely the motor is a 180 volt DC but I have not looked at it. I like the VFD as there are options like soft start, instant stop if motor is equiped with a brake, as well as the variable speed with in the limits of the gear/belt position selected. Our rolling mills and other stuff use VFD, usually in the larger sizes 5 HP and up.

Thanks for the responses guys. I will stick with my original plan of 3 phase and VFD. Just have to save those nickels as pennies are not used anymore.
Pierre
 
Ed T said:
All good input above. I have wrestled with the variable speed option as well and I have a few observations:
1) I have had a 100v DC motor on my cheapo drill press for about 20 years and it works OK to drop the spindle speed down to speeds more appropriate for metal work. I think I set the pulleys at the lowest speed when I put the drive on and I've never needed to change it to do what I want to do. I do use the variable speed a lot as I change drill sizes, but not the step pulley. Haven't worn out a set of brushes yet.
2) It's been a long time since I took physical science, but, as I recall, the formula for horsepower is HP=RPM X TORQUE/5252. So, a 2 HP motor develops 2 horse power at some RPM when it's making some amount of torque. In the case of a fixed speed AC motor that fixed speed is the RPM in the equation. If you start to manipulate the RPM with some outside device like VFD or a DC controller the horse power the motor develops will drop accordingly. The torque a motor develops is directly related to the current that the motor is absorbing. When you drop the effective voltage to the motor, the current drops and the torque and HP go along with it. Some controllers have a "torque control" setting which may help to mask some of the effects of the above, but the fundamental issues still exist. I'm not sure exactly what happens when you overdrive a motor with, say, a frequency higher than the nominal rated frequency. It should make more power, but It's probably not directly proportional and may have some other detrimental effects (heat). Most of you probably melted a small DC motor by over powering it with high voltage so that's the direction I'd expect things to go. Goes fast as hell for a moment and then all the smoke leaks out.
3) While the infinitely variable speed option sounds like a cool thing, I don't find myself changing the step pulleys on my mill very often and the three speeds on my lathe seem to be adequate. Keep in mind, I'm just making hobby parts and I'm not trying to get 110% out of any of my machines. If you really want to maximize the efficiency of your operation, the variable speed may be a good option, but for less intense use, it may just be an added expense and another board to go bad.
Click to expand...

While I don't care much for treadmill motors, I'm a big fan of industrial dc motor drives. I have these on my drill press, wood lathe, atlas mill, mini-mill. I can't say enough good about these setups. BUTTTTT- THEY ARE VERY EXPENSIVE. I've been lucky to score used one thousand dollar setups for $50 off scrapped industrial equipment. Probably the most useful is my drill press. I have a big enough motor that I can go slow enough to tap soft materials, yet without changing belts, I can spin it up for tiny drills.
You notice that I didn't mention my metal lathe . I'm content with having 3 speeds and backgear. When given the choice to replace the motor that the smoke got out of, I simply went with a newer single speed continuous duty package and am happy.
On the other hand, the variable speed I have on my horizontal mill is a god send. I can tune it to just the right sweet spot depending on what cutters I'm using. I wouldn't be without it.
 
weighing back in again, LOL

OK so my lathe is a Gosan 1440V http://www.shyesheng.com/products_20-17Series.asp , 3 HP 3 Ph came factory stock with a Delta VFD. It has two speed gear box and the speed ranges are, 30 - 405 and 165 to 2200. I am using the dial on the VFD frequently to speed up or slow down the unit and often switch from High to low, especially when parting off or threading. The one issue I had was that the VFD was not sized to operate it from single phase, so my options were to replace the VFD, and add another for the suds pump, or feed the lathe from a RPC. Based on my "other" equipment concerns, I went with the RPC and have been very happy with my decision. (OK so I wish that I had gone with a 10TZ instead of the 7TZ as very quickly I realized that a bigger RPC would have been better as I added more stuff.)

DC Motors, I repair power tools and machinery for my living. When the first treadmill came in for reapir, I looked at it and replied, OK, looks like a big belt sander, I am sure I can handle it. Since then I have repaired hundreds of treadmills and other exercise equipment. I have on occasion tried retro-fitting those motors to other applications and generally, I am not impressed as the speed and power of the motors does not lend itself to many other applications. also reversiblitly can be a factor, often the motors are offset wound, so they have a much higher forward torque, but when run in reverse they are almost in neutral and have very limited power. To get an idea of how this works, look at some of the power tools that have a forward reverse switch, that rahter than electrically reversing, they use a brush shifter. Rotate brushes all the way one way for forward, then as they are shifted back the other way, the motor slowly looses power until it stalls then slowly increases power in the reverse direction until the brushes are all the way around the armature.

I tried to install a 1/4" HP Industrial DC motor with an industrial KB Pentapower controller on my 4 speed 24" Beaver scroll saw and found that at even with the belts in the slowest speed range, with the DC motor turned down slow it did not have the umph to get itself moving properly and was jerky as the speed started up. If the speed was set high enough it ran just fine, but then it did that with the regular motor on it as well, so it is running with a regular motor, waiting for me to trip over a VFD and 3 phase motor that will work. Slow speed is for cutting metal and for filing with it.

Now back to treadmills as you mentioned that the treadmill was a 240V unit. There are treadmills that are made with 3 pahse motors and VFD drives. These are the more commercial units like the ones found in hospitals for stress tests and in commercial gyms. These motors are idea for other applications, except, they are open frame motors. Not even generally open drip proof, just open cage frames and they need to be protected from debris if used in other than "designed" applications.

Walter
 
Hopefully an Electrical Engineer will correct me if I get this wrong. I have a Hitachi SJ200 VFD, rated at 3 HP and it is managing a 2 HP, 6 pole (1200- RPM) 3 phase motor rigged on an old Arboga drill press. The Euro style internal Arboga motor had long since fried, the gear box hit with a fork lift, and so $20 bought it from the scrap heap. I reworked the dive system with a belt and pulley set up. The VFD unit is fed 215 volt single phase and it converts this to 200 volts 3 phase. As I interpret the handbook, the motor will develop nearly full torque at virtually any RPM.

In practice, the machine definitely seems to "rip through" steel at low RPM settings. It takes just a second to reach the speed that is set, but that can probably be reprogrammed, I have it running and I'm no programmer.... It would appear that the claim of nearly full torque at all speeds is accurate. The SJ200 is obsolete due to changes in the feedback and network features of the newer units. Since the application here is just to run one motor and I don't need to know all the operational parameters, this is fine. The latest units have a plethora of features (and the SJ200 way more than I will ever need or use).

My point is that compared with a DC motor where current is the key to torque, things can get real hot at low RPM. So far on the Arboga the 3 phase motor has shown no signs of overheating. If the windings pull too much current, the Hitachi will alarm. This feature is programmable into the VFD, just enter the full load motor rating from the nomenclature plate and save the setting. It was made clear to me to go one motor size HP higher in selecting any VFD. If you wish to run a one HP, get a 2 HP rating, 3/4 HP, go one HP, 2 HP get a 3 HP, and so on. This VFD is an impressive device. Geoff
 
110octane said:
Hopefully an Electrical Engineer will correct me if I get this wrong. I have a Hitachi SJ200 VFD, rated at 3 HP and it is managing a 2 HP, 6 pole (1200- RPM) 3 phase motor rigged on an old Arboga drill press. The Euro style internal Arboga motor had long since fried, the gear box hit with a fork lift, and so $20 bought it from the scrap heap. I reworked the dive system with a belt and pulley set up. The VFD unit is fed 215 volt single phase and it converts this to 200 volts 3 phase. As I interpret the handbook, the motor will develop nearly full torque at virtually any RPM.

In practice, the machine definitely seems to "rip through" steel at low RPM settings. It takes just a second to reach the speed that is set, but that can probably be reprogrammed, I have it running and I'm no programmer.... It would appear that the claim of nearly full torque at all speeds is accurate. The SJ200 is obsolete due to changes in the feedback and network features of the newer units. Since the application here is just to run one motor and I don't need to know all the operational parameters, this is fine. The latest units have a plethora of features (and the SJ200 way more than I will ever need or use).

My point is that compared with a DC motor where current is the key to torque, things can get real hot at low RPM. So far on the Arboga the 3 phase motor has shown no signs of overheating. If the windings pull too much current, the Hitachi will alarm. This feature is programmable into the VFD, just enter the full load motor rating from the nomenclature plate and save the setting. It was made clear to me to go one motor size HP higher in selecting any VFD. If you wish to run a one HP, get a 2 HP rating, 3/4 HP, go one HP, 2 HP get a 3 HP, and so on. This VFD is an impressive device. Geoff
Click to expand...

Hi All
I am new to the forum & will be greatfull for any info thanks.

I have just got a viceroy 11x24 lathe, with a 1.2 Hp motor 3ph & will be getting a VFD unit to run the motor.
reading this post & others i have got a lot of info on VFD's, not all ponting the same way.

1, a VFD with adv flux vecter control will develop nearly full torque at virtually any RPM.
but a std one will not, is a vector control a must. yes or no ????

2, is a IP65 (dri box) needed in a unheated room or garage (some say it is a must have) or will a IP20 (not a sealed box) be ok. Y/N

3, i was going to get a 3 Hp VFD for the 1.2 Hp motor, but may put a 3 Hp motor on, at a later date.
so do i get a 4 Hp VFD or not.

thankyou, great forum.
jeff
 
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