Using Inverter Duty Motors for the first time.How different are they?Do they run hot?

Good Evening ,

I am using Inverter Duty Washdown Motors for the first time for a small project. How different are they ? It is a 5 hp and normally the FLA is 7.6 amps. The 5 hp is connected to a SEW Gearbox , and has a die connected to the gearbox. At the moment the motor is drawing 4.2 amps , and still does not have product on it.

Do Inverter Duty Motors run hotter ? I had the motors running for about 2 hours with really no load , and they seem very hot. It is a Baldor and on the name plate it shows Mag. Current at 230 VAC is 7 and at 460 VAC is 3.5 . What does Mag Current mean ? Also , on the nameplate is the FLA and for 230 VAC 13.4 and for 460 VAC is 6.7 amps.

Thanks so much in advance for your helpful information ,

That is the magnetizing current required to get the motor spinning.

You are under FLA so you should be fine. Any motor running for 2 hours is going to be warm.

As a general rule, motors designed to NEMA MG1- Part 31 are designed to better handle the rigors of being run by inverters; added heat dissipation capabilities, less cooling required at reduced speed and better winding construction methods such as higher magnet wire insulation ratings, phase paper in the slots, dipped varnish etc.

Unfortunately, the term "Inverter Duty" has no official definition enforceable by anyone, so companies have over used it and rendered it virtually meaningless. When Baldor was Baldor, they seemed to care a lot more about defending the terminology, but I have noticed that since being bought out by ABB a few years ago, that has all gone out the window. If the motor specifically SAYS it meets NEMA MG1 part 31, then it likely does, but I have seen Baldor selling motors and saying they are "inverter ready" or "drive duty" or other terms that people ASSUME mean the same thing, but don't. I've done 3 projects in the last 3 years with a lot of Baldor "inverter ready / duty" motors where there were multiple motor failures within months of the initial commissioning. Baldor tried defending them by blaming the installation, or blaming the non-Baldor drives, but in each case they have eventually admitted that there were "deficiencies" in the products. In the last one we did where over 50% of the motors failed within 3 months, we took one motor apart and saw that there was no phase paper, no special cooling, no better bearings, nothing that would have made it NEMA MG1 part 31 compliant. But... nothing in their literature actually said that! They said "inverter ready" or in another place, "inverter duty", but no mention of what that meant.

So bottom line, look for something saying it meets NEMA MG1 part 31, don't fall for marketing tricks. In addition, something not covered by the NEMA guidelines is bearings. Running motors in VFDs can (but not always will) cause a voltage gradient to build up between the stator and rotor, so energy flows between them, through the bearings and races. It's very low energy, but microscopically the energy transfer looks like little weld marks and the damage builds up until the bearings fail. there are several things that can be done about it, some of them good for retrofitting. But it's best practice to address it up front BEFORE you lose the motor by specifying either isolated bearings (i.e. ceramic races) or shaft grounding bushings built into the shaft seals.

Rant complete...

This is not a motor bashing thread but I'v said it before and I'll say it again!!!

Baldor motors are JUNK with a capital J! Iv had more late night call ins for failed Baldor motors than anything.

SEW, now there is a motor! A price tag to with it, but never do I get calls for failed SEW motors.


Just a quick question about your motor "getting hot".. Is this a fan cooled motor? Or enclosed type? I have enclosed types that will fry eggs. Lots of things can cause heat other than the motor as well. Noise or reflected wave issues, did you use drive cable?? Reactors? Is this a new gearbox as well? Could it be binding or dry of oil?

Just a few thoughts.

Did you auto-tune the drive to the motor?

If the drive is in V/F mode, and the boost voltage is too high, and you are running at low speed, the motor could be receiving excess voltage, which will cause excess current draw.

However, pulling 4.2a with a rating of 3.5a magnetizing current and 6.7a full load should not be a concern for a machine that is running idle.

How hot is hot? My normal advice for motor temperature is when running full load for an hour or so, you can touch the motor, but you probably don't really want to hold onto it

http://toshont.com/wp-content/uploads/2017/06/Motor-Temperature-Rise.pdf

I think this will help

The warmer motor may have nothing to do with the VFD, but may be a result of a combination of speed and load.

Motor heating is I^2 R. It is independent of speed. The cooling mechanism of the motor, for example the external fan, is dependent on speed - a slower motor means less cooling air flow and therefore higher temperature.

Current is a function of torque demand on the motor, which is determined by the load. A conveyor is a constant torque load, and therefore constant current. It will generate the same same amount of heat at low speed, and with less cooling will run hotter. A centrifugal fan is a variable torque load, and at lower speeds it will generate less motor heat. If the cooling capability falls off faster than the current the motor may still run hotter at lower speed, but it isn't as much of a problem as with constant torque loads.

Or, you could have harmonics on the load side generating extra heat.

First, the OP didn't say that the motor is running on inverter power.
Second, NEMA insulation Ratings on commercial/industrial motors are Class B, F, and H. Class B permits insulation temperature (that's ambient plus rise) up to 125 degrees C. Class F is 150% C, and Class H is 175 degrees C. Note that water boils at 100 degrees C. Even a Class B motor running at 80 % load will burn a piece of meat off your hand. Forget that "if you can hold your hand on it" nonsense.

Regarding Baldor's "inverter ready, inverter rated, and even inverter duty" marketing terms, they have been wildly abused and overrated as long as I have been working in this field. This could be safely said of pretty much everybody else except the old Reliance too. I don't see where ABB joining Baldor affected it either way. The bottom line is just as Jraef has said----MG1-P31 is the only thing you can really trust (no influence from the marketing people!). If it doesn't mention MG1-P31 on the nameplate or in the specs, just walk away. You can't know anything about it's suitability on PWM power.

Third, running an Inverter Duty motor on sine wave power should result in the same motor temp or maybe a little less due to improved cooling. On PWM power you can expect the motor to run warmer , all other things remaining equal, but still within the temp limits of the Insulation Class.

Fourth, magnetizing Current is one of the two currents feeding induction motors---the one that magnetizes the coils. The other current produces torque in the motor. Unfortunately, these two currents are vectors and are 90 degrees apart from each other. Further description of this should probably be done elsewhere because it gets pretty messy.

One concern I just found out today is , we have a product that we need to run two die rollers that we need to run at 12 rpm . To accomplish this I am going to need to run this motor at 3 HZ . I ran these motors with the die rollers for a few hours and did not show any issues . Are Inverter Duty Washdown Motors capable of running at 3 HZ ?

Thanks so much for your advice .

I'm no expert by any means, but I think you would run into problems running consistently at 3hz. The times I have set up systems, we would add cooling fans if we expected to run under 10hz consistently. I would also think the available torque would be really low at that speed unless it has an encoder and running closed loop.

What is the overall speed range that you expect to operate in? You might need to look at changing the overall system ratio. That could be by changing gearbox ratio or the drive components connected between the gearbox and die.

Rob S, the answer to your question lies in the labeled enclosure type---in this case TENV. A TENV is capable of cooling itself without regard to shaft speed---there is no shaft fan.
As to available torque, an induction motor is basically a constant torque device at any speed from base speed down to zero insofar as its magnetic capacity is concerned. It's ability to deliver that torque is limited by its ability to cool itself primarily. On PWM power, the motor needs to be excited in special ways at frequencies below 3hz to make that level of torque available and make the shaft rotate smoothly. I would only trust the best of PWM drives to do this reliably.

Rob S. said:

One concern I just found out today is , we have a product that we need to run two die rollers that we need to run at 12 rpm . To accomplish this I am going to need to run this motor at 3 HZ . I ran these motors with the die rollers for a few hours and did not show any issues . Are Inverter Duty Washdown Motors capable of running at 3 HZ ?

Thanks so much for your advice .

Click to expand...

I can't explain the science as well as others can, but I will tell you that if you plan to run a motor at 3hz, make sure you have a couple of spare motors on hand. Your maintenance people are going to need them.


Bubba.

Regarding willxfmr's statement about motor failure above, consider that 3hz is 1/20th of 60hz which, in motor manufacturer language, is a 20/1 speed turndown ratio. By willxfmr's statement, any manufacturer putting a turndown ratio of 20 or more on their nameplate is simply lying or being careless with their warranty reputation.

Judging by the massive number of motors nameplated 20, 40, 100, and even 1000/1 turndown ratio, willxfmr's statement appears to be shear nonsense. And it is. Sorry.