New motor and VFD, need advice

[bilinghm]

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

[mxtras]

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

[Al_The_Man]

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.

[mxtras]

Excellent info!

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

Scott

[in2steam]

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

[bilinghm]

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.

[aspenelm]

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.

[bilinghm]

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

[in2steam]

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

[in2steam]

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

[bilinghm]

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

[bilinghm]

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