With my new Leeson 2 hp motor & Hatachi VFD in place I need advice on the appropriate speed range that is practical with such a set up. The motors' 60 cycle speed is 3500 rpm, and I would like to achieve the goal of seamless variable speed control from a low of 100 rpm all the way to 2500 os so without touching a belt. I have a full array of belt ratios available with the original 12 speed pulley arrangement, but I want to "set it and forget it". Does anyone have experiences with this that they will share? What speed ratio did you set the machine at? How slow can you go by just turning down the cycles? Does the machine work properly at all speeds? Does the motor get hot when running slow?

Thanks,

Bill

Well - in a nutshell, the slower the speed, the less torque you will have. That sounds pretty obvious and you already know that. You can run the motor pretty damned slow, but you will be able to stop it with one finger so it's really basically useless for doing any work. The nice thing about the arrangement is that if you try to keep the motor in the top 75% or so of it's RPM, you can adjust to suit conditions - on the fly.

I have a VFD on my Bridgeport, and I run it from very slow speeds for tapping all the way to max RPM. The nicest thing about it is you can get the speed close with the belt arrangement and then fine tune it as you cut.

Yes - the motor does get a little warm at low RPM.

Scott

The trouble is the term VFD is a loose term, as it can be everything from just variable frequency drive (with no form of feedback, electronic or otherwise).
and a Variable Frequency Drive which will fully emulate a DC motor down to zero speed. Such as modern Vector drives will.
These VFD's can be used in crane lift applications where a load can be held stationary, a job previously not possible without the typical wound rotor AC motor and Brake.
Also they have been used in elevator applications.
In most cases a sensorless vector VFD will do the job, if not, one with encoder feedback will often do the trick.
If used down close to zero, a fan will be required for cooling.
With a modern vector drive, the internal processor will produce a model of the motor during tuning, and then attempt to keep a constant vector angle to maintain maximum torque, based on the current, frequency and other factors.
Modern CNC AC motor drives are also a testiment to this, Mitsubishi etc.
Al.

Excellent info!

I made the assumption he was discussing a relatively low cost, no-frills VFD - perhaps he was not. Bad assumption.

Scott

2 pole motors, esp those in the 2 HP range tend have there best power band starting at around 2500 rpm up to full load speed, which I would assume is around 3450. When I worked for lesson, as engineering tech in there dyne lab we found that many of the motors in that HP range were closer to 2.25 in alot of cases. This depends upon the class of motor it is, and its general design of course, lesson made several motors which did not like VFD's (I must admit the ones we were using were rather simplistic and old) at ranges of 25Hz or less, these tended to be older designed prevouis to VFD's. A 2 pole motor esp one thats TEFC will get real hot at load going that slow(around 1200 rpm). If you start adding torque boost, or vectoring it may get real hot even with an added fan. Personally best bet would have been to go 4 pole(1800 rpm) 1 HP or greater, as they would have the same torque rating as the 2HP at desired rpm of 1800. You would loose HP advantage over the rating for the motor at 60 cycles as torque flat lines but you could at least spin it up faster, typicaly they will run well untill 110 cycles if you are lucky 120 through belts.
you will find that this motor is going to be not as useful for slow speed operations for instance tapping around 100 rpm(lets say around 300-500 rpm input) and then be able to run back up to 2000 RPM(about 5000-6000 rpm). It would be almost usless at anything less then that, not to mention not very smooth depedening upon the drive. And conversly at high rpm you will have some heat issues but bearings may be of prime importance as most motor bearings can only handle about 5k rpm unless designed for such duty if you can get the motor to spin that fast. You might be able to get it set into a range of belts maybe only swaping one or two around, but more then likely not the full range you are looking for. I am of course discounting the drive, becuase those can add some benefit such as vectoring and torque boost, but the motor in this case would be more of a problem then the drive IMHO.
chris


chris

The motor is a Leeson catalog number G120088.00, 2 pole 3600 rpm fully enclosed fan cooled. The drive is a Hitachi SJ200 sensorless vector drive.

So If I understand correctly, the recommendation is to select a belt setting that produces the slowest usable speed at around 25-30 cycles and overspeeding the motor to achieve the top RPM range? I called Leeson and they said that this motor is designed for VFD use and is normally usable from 6 to 60 cycles with no danger of overheating. They also reccommended that the upper limit be kept to about 75 cycles.

bilinghm, do you know why the upper limit is 75hz? is it due to balancing or something else? I have the same drive and a 1825rpm 3hp motor that I would like to run at 2500 rpm for a blower application, which would exceed the 75hz.

The leeson catalog says it is reccommended that 2 pole motors should be limited to 75 hertz unless they have special preparation. That would be a 25% increase, so about 4,500 RPM? I understand that some 1,800 RPM motors can handle 120 hertz (100% increase) but that is still only 3,600 RPM. Maybe they are in danger of will throwing a winding.

Bill

The motor is a Leeson catalog number G120088.00, 2 pole 3600 rpm fully enclosed fan cooled. The drive is a Hitachi SJ200 sensorless vector drive.

So If I understand correctly, the recommendation is to select a belt setting that produces the slowest usable speed at around 25-30 cycles and overspeeding the motor to achieve the top RPM range? I called Leeson and they said that this motor is designed for VFD use and is normally usable from 6 to 60 cycles with no danger of overheating. They also reccommended that the upper limit be kept to about 75 cycles.

Then go with there recomendation, thats sounds like an IRIS motor(is it black?), although its been some 5 years since I worked for them, 75 cycles sounds more like a bearing limit then a motor limit per say. I would go with 25 as the real low end unless you can deal with not so smooth running and low torque, although it maybe handy to run below that for indicating and such. Its not an exact science unless you have them do a matching, I only did that once when I was in the lab and it was little more then an engineer pulling 3-5 motors he thought would work, then test results dictated what he picked or a range of such. Many of there older motors predate accurate tests and I was in the process of testing alot of older motors for CSA and UL for standards, welll that was untill the 9-11 and layoff shortly there after.
The IRIS motors did a good job disipating heat and had the insualtion to help with corona effects from the drives. I really only saw a couple of those, they were introduced before I started to work for them so most the testing was done. TEFC motors may draw alot of current up at the high end due to the fan, as its dynamic the more you spin it the more it draws, thats the only other reason it may not be recomended above 75Hz that I can think of, if you can keep your carrier lower, although it makes more noise it tends to run cooler, although not always! If you have a way to measure if the houseing reaches 150'F (65'C)then you are getting to warm esp for run of several hours. The maxium internal temp should not go above 150'c on the coils.

chris

The leeson catalog says it is reccommended that 2 pole motors should be limited to 75 hertz unless they have special preparation. That would be a 25% increase, so about 4,500 RPM? I understand that some 1,800 RPM motors can handle 120 hertz (100% increase) but that is still only 3,600 RPM. Maybe they are in danger of will throwing a winding.

Bill
4 pole motors can handle over 120 Hz if the winding is capable, the problem is that the frequecy exceeds the ablity of the motor to translate the torque(properly stated the rotor currents are too chaotic), hence it stalls almost instantly at that point, I installed a 4 pole TENV motor in a conveyor a year ago and it could only handle 93 Hz after that it just stopped and sat there, tried a smiiliar motor and it ran to 110Hz, but it lacked the mounting I needed so I was stuck with 93 Hz topend.

The winding is actual called a stator, its stationary on the frame, the rotor, is on the shaft and is laminated steel pushed together and welded, I have never heard nor seen a small motors rotor coming apart, it would take alot of force I would say the endbells would be destroyed long before that would happen, the biggest concern in reagrds to the rotor is that it becomes to hot and warps and starts to touch the stators own lams, in which case you get a rub, I have seen that happen, alot, typically a overheat condition but also overvoltage has caused it, generally the motor is junk at that point.

chris

I am doing the basic programing of the Hitachi SJ200 and have hit a snag. One of the parameters that must be set is referred to as "setting the motor current". The Hitachi manual says that The motor's current rating will appear on the manufactureres name plate. I can find no such current rating. Is there another term for this parameter? Could the equivalent Leeson term be "P.F."? P.F. appears on the nameplate and is shown as 85.2.

Bill

Answering my own question: I talked to Hitachi and they said that the "current setting" is the same as the "full load amps". They reccommended that I leave the setting at the default of 8.0. They also had some specific setting recommendations for an inverter powering a milling machine:

Parameter A042 set to 00 (manual torque boost)
Parameter A044 set to 00 (constant torque)
Parameter A081 set to 01 (automatic voltage regulation)
Parameter B130 set to 01 (over-voltage LADSTOP enable)

I am doing the basic programing of the Hitachi SJ200 and have hit a snag. One of the parameters that must be set is referred to as "setting the motor current". The Hitachi manual says that The motor's current rating will appear on the manufactureres name plate. I can find no such current rating. Is there another term for this parameter? Could the equivalent Leeson term be "P.F."? P.F. appears on the nameplate and is shown as 85.2.

Bill

PF is power factor. Don't know why there is no nameplate amp rating. 8.0amps seems on the high side, because my 3hp baldor motor is rated for 8.2 amps at 230volts. The parameter setup for milling machine are nice to know.

I am doing the basic programing of the Hitachi SJ200 and have hit a snag. One of the parameters that must be set is referred to as "setting the motor current". The Hitachi manual says that The motor's current rating will appear on the manufactureres name plate. I can find no such current rating. Is there another term for this parameter? Could the equivalent Leeson term be "P.F."? P.F. appears on the nameplate and is shown as 85.2.

Bill

PF is power factor, thats a normal nameplate things along with amps and volts. Typical PF is around 80-90% motor depandant. PF is the amount that a motor lags the voltage, typicallly run cap motors have the best PF, but these of course are single phase, you can run some of them with inverters.
Since you answered you own question I don't need too.

chris

PF is power factor. Don't know why there is no nameplate amp rating. 8.0amps seems on the high side, because my 3hp baldor motor is rated for 8.2 amps at 230volts. The parameter setup for milling machine are nice to know.

Your 3HP motor, electrically speaking only is more like 2.75 HP. Typically a single 3 phase HP is around 3.1 amps on 230 and 1.5 on 460. This also depends upon the number of poles and the design class (a,b,c,d), its duty cycle, Full load RPM and enclousre type(TENV, TEFC, etc). Lower pole motors draw more current, or atleast they tend too, there are always exceptions, and this would be more a rule of thumb. There are alot of gray areas when it comes to rating motors, lots of fudging. The problem with motor ratings is that an engineer determines what the HP will be before the motor is ever made, all test results are determined from that point, sometimes they are way off and have to be rerated, but more often they just go with what they had.


chris

I finally got everything hooked up, adjusted and ready to run. The pulley selection I fitted provides 2,500 RPM at the spindle when the motor is turning 3550, the full 60 cycle
speed. So I have been experimenting with this arrangement and the results are very positive. I put a 3/4" endmill in the collet and took some cuts on a big bar of mild steel at 10 cycles. The cuts were fine and the machine performed without protest, plenty of power. It seems that the goal of no belt changes and sufficient power for all operations, low to high speed, has been achieved. On a side note, I eliminated all of the additional pulleys and belts, I run just two pulleys and one belt instead of the previous set up of four
pulleys and three belts. The difference in smoothness is exceptional.

Thats good to hear, what kind of machine was this anyway?

chris

The machine is an Enco 90001 round column mill driil from the mid eighties. Old but stiill working fine.

so 10 cycles nets you around 410 rpm at the spindle. so you are using the constant torque setting instead of sensorless control. good to see that it worked out for you.

Your 3HP motor, electrically speaking only is more like 2.75 HP. Typically a single 3 phase HP is around 3.1 amps on 230 and 1.5 on 460. This also depends upon the number of poles and the design class (a,b,c,d), its duty cycle, Full load RPM and enclousre type(TENV, TEFC, etc). Lower pole motors draw more current, or atleast they tend too, there are always exceptions, and this would be more a rule of thumb. There are alot of gray areas when it comes to rating motors, lots of fudging. The problem with motor ratings is that an engineer determines what the HP will be before the motor is ever made, all test results are determined from that point, sometimes they are way off and have to be rerated, but more often they just go with what they had.


chris
I missed this post, but yes, I figured each motor varies a bit. FWIW, the baldor motor is 1750 rpm, 8.2A @ 230v, TEFC, class F, 182T frame, 1.15 service factor, 87.5% efficiency, 78% PF, and rating of 40C AMB CONT. I have the 3hp SJ200 which gives me 4.3 kVA at 230v, with 11.0 amps cont. output. How much juice can I safely run through the motor? The application is for a woodworking dust collector blower for home use, so it will be intermittent use for up to an hour at a time. I need to get as much hp as I can get from this motor, the blower impeller is rated for around 3500rpm. Sorry to sidetrack, but somewhat relevant.

This application being a bit different from the likes of a Mill etc, I would think it is probabally critical that you do not exceed the F.L.A. of the motor, If you can get hold of a Clamp on ampmeter you could see what the Maximum present current is at 60hz, this will be with both intake and exhaust as unrestricted as possible,
Then take it up gradually to 120hz and see what the effect on current is.
I would think the tendency for the current to climb will be offset by the increase in impedance.
Any restriction of the intake or exhaust after this should decrease the current proportionately, presuming it is a centrifugal impeller.
Al.

thanks al, I will try that when I have the dust collector body assembled and ductwork run.

If your drive has the setting, turn it to constant HP, since this load is dynamic, they may word it in different ways, vectoring will be of little use to you in that application. As far as "juice" goes, your drive won't really let it get more then it can handle if its set properly, you can fudge the settings but its been my general experience that you can't really fudge the numbers to far outside of what the nameplate states. The motor itself is the biggest limit as to what it will draw, as long as the line voltage is steady(most drives don't increase over rating or input) its only going to draw so many amps regardless of what you try and do with the drive although the drive might let you over volt the motor some. As for over 60 Hz threshold your amps will go up to the roof, it may not be possible to get that motor to 120 Hz, the torque will increase ever rpm faster that motor spins(assuming its a centrifugal blower). When I said what class is the motor your response was with the insulation class of F which is good for your use, but there is also a motor class, in your case I think its C but I am only goin on what you have provided. This would make this motor a compressor duty motor, they respond well to a mild to heavy torque at FLA but don't like over or under speed as much(they are designed to have higher torque so the amps go up), which means this motor will more then likely not like the increase in Hz and result in higher then required amp draw in those areas. If you are doing the Bill Pentz design you may need to switch to a 2 pole motor even at half and 3/4 speed that will not draw anywhere what you need for CFM. I think the clear vue guys are running 5HP 2 pole lesson motors, I could be wrong though. 182 frames like to be torquey motors, your amps indicate also that this motor would be better suited for such, you HP will not go above 3 it flat lines at the 60 Hz threshold torque will only reduce from that point esp bad in dynamic loads. If I were to take a jab at 3 HP you might make it to 75 HZ before preforamce degrades since its 1.15 SF motor.

chris

Looks like I have some testing to do. I also have a 3450 3hp motor that would work as well. When I get some results I will start a new topic. And yes, it is a Pentz collector.

Yeah then I would go with the 2 pole motor, 3 HP nema class B or C would be best(I think 4 is min really for multiple inlets) anything less you will not get the needed static pressure and a suitable vortex, they have tons of info on the clear vue and pentz sites I suggest you read it all, one day off in the future when I get rich (quickly) I hope to build one so let us know. I am hoping to buy the clear vue mini (cv-o6) for a router table I am building after I get done with my mill.
chris