Low power - motor or VFD?

[Aries37]

On all of my installs I don’t use wire nuts on the motor connections, but instead use ring terminals crimped to the wires then attached together with appropriately sized machine screws and nuts. It’s more work and requires taping the finished connections but insures a solid trouble free installation. Most motor junction boxes are always too small and when you bend the wires to put them in place the wire nut connections tend to come apart. All wiring should be stranded conductors and not solid.

 

[datosi81]

Success! I think anyway...Parameter 13 “torque compensation with range”. I couldn’t find much info on this parameter and the vfd uses a range of 0.0-4.0 on this parameter. So I really wasn’t sure where to go with this one.View attachment IMG_2025.jpg


It gives that warning that this setting could cause damage to the motor so I was hesitant to try. It turns out the factory setting was zero. I increased it to 1.0 and there is a world of difference. I think I’m going to reinstall the motor and see how it does with the belt on. Maybe 1.0 will be sufficient. I don’t want to push it to far....if I even knew what too far is. It doesn’t specify what the numbers in the adjustment range mean so I’m not sure

 

[Nick Hulme]

It sounds like some sort of current compensation to maintain torque.
Good to hear you've got a potential solution.
If you run the motor for a good while and it doesn't get overly warm you're not driving it with too much current

 

[Herbiev]

Well done finding the fault. I've got a KOC100 series VFD which came with a 172 page manual and it took me ages to reset all the parameters to get my three phase 2 hp motor to run correctly.

 

[datosi81]

Well done finding the fault. I've got a KOC100 series VFD which came with a 172 page manual and it took me ages to reset all the parameters to get my three phase 2 hp motor to run correctly.

They gave the opposite problem lol....I don’t know why the manual only goes to parameter #35....unless of course, that’s all the parameters adjustable in this vfd [emoji52]

 

[Aries37]

Great to hear that you may have solved the problem. I would agree with Nick that this setting is internal compensation for current/torque. Also noted the HZ settings available are way above 60 Hz. Older motors like you are using need to be at the 60 Hz settings, otherwise you run the risk of over current and motor burn out. Further you should have a voltmeter to check voltages between phases at the motor. They should be close to the input line voltage. The current draw on each phase should be measured with an Amprobe, close to the FLA rating on the motor. These readings will vary depending on how the VFD is set, meaning at what HZ the motor is operating at. Motors not rated for VFD use will overheat and draw more current when operated in the 20-30 HZ settings for long periods of time so it’s a matter of striking a balance by some extensive testing while under load on your mill.

 

[datosi81]

Now that it seems to be running better I’m gonna check the output voltages again and check the current draw. What do you guys recommend as safe minimum and maximum hz? I won’t hold it against anyone if the motor gets fried lol. Aries, are you saying to not exceed 60hz at all and to keep the minimum above 30?

 

[Aries37]

My previous post stated the reasons for holding close to those parameters.
Older motors, like you are using, were designed for 60 Hz and not rated for VFD use, however most of them will work OK if they are wired and set up correctly.
I would further suggest using line and load reactors, referred to in one of my previous posts. The design and function of VFD’s puts stress and loads on the copper windings and insulation. Frequencies beyond the 60 HZ settings makes things worse. If you were to purchase a new motor rated for VFD use, the manufacturer has accommodated these requirements in the design of that motor, therefore they cost more.

 

[datosi81]

That sounds reasonable. The main reason I went with the vfd to begin with was to be able to use the 3 phase motor in my garage, I was looking at speed control as a fringe benefit. I think I’m gonna use the setup as is and see how this old motor does. If it some point down the road the motor starts giving me trouble, I’ll upgrade to a newer motor and utilize the speed control at that point.

 

[Wizard69]

One big issue with VFD is knowing the maximum rotor speed a motor can handle. With modern motors you can reference the motors data sheet, with older motors you might never be able to find out because the assumption was they would run on 60 Hz. So you do run the risk, when going past 60 HZ, of over speeding the rotor and grenading it. How far beyond 60Hz that would be is unknown but with drives that can do 400 Hz it is a real possibility.

Another issue that you will run into is the winding insulation on old motors is subject to punch through form high voltage spikes as a result of the fast switching the drive does. This is compounded buy older motors often having degraded insulation to begin with. You can reference the drives manual to see if they have any suggestions for remediation of this electrical noise but in the end it just means your (actually the motors) life span won't be as long as a modern motor.

In the end I wouldn't worry about motor life as long as you don't get excessive with speeds over 60 Hz. In the end you are operating an old motor with an unknown number of years left in its lifespan. I'd enjoy it for as long as possible as in a hobby shop it might last decades longer. Or it could die tomorrow.

By the way you will enjoy having variable speed. It is surprising how nice it is to have even if you have to shift gears from time to time to get more torque for low speed operations.

 

[Aries37]

That’s why, on older motors, I always use line and load reactors. Yes, it costs more, but I’ve never had a motor failure after many years and many hours of run time. Additionaly keeping the speed maxed at around 60 Hz provides that extra assurance that the motor will siurvive. The newer VFD rated motors have windings, laminations, insulation and specific cooling designed for this use, plus you can run them at those high HZ settings with no damage. That’s why they cost so much more than conventional designed motors.

 

[ddmckee54]

Aires37 hit upon what I consider to be the major problem with motors on VFD's - cooling. I design industrial controls systems for a living, been working in the industry since the mid '70s. Sure you can turn a motor with a VFD over at ridiculously low RPM's, but you can't do it 24/7 for weeks on end. The reason that it's not recommended to do that is the fan on the end of the motor. That fan is usually the only way the motor has to cool itself off. If the fan's not turning fast enough it won't move enough air and the motor will overheat cooking itself. The number that I hear tossed about most often for minimum motor speed is 15-20Hz. I'm kinda conservative so I try to not go below 20Hz.

I'll get off the soap box now,
Don

 

[Aries37]

Don, you are absolutely correct on what you stated. I’m a bit more conservative in that I keep the minimum speed around 30 Hz. Torque ratings drop dramatically at those lower HZ settings anyway.
And again, with non VFD rated motors, you have to check the voltage, FLA ratings and the temp.rise. All of this info on the motor nameplate. Keeping operating conditions within these specifications will ensure longevity. Further, I always recommend getting motor windings “megged” at the local motor shop.

 

[Nick Hulme]

I have a 1hp motor driven by an old LED display Siemens Micromaster Vector on my Myford Super 7, here's a video of it running you might like -

https://youtu.be/CgHcv8nk-gw

That's turning Aluminium at 10Hz.
Primary drive belt is on High Speed, Final Drive belt is one down from top speed, this demonstration clearly shows how dramatically torque drops off at low speeds

Whilst you wouldn't run like this for extended periods without external cooling and a temperature sensor hooked up to the drive I've used Jog, which is set to 2Hz, for tapping M8 in 304 Stainless parts for significant batch sizes and since the duty cycle works out low regular checks on the motor temperature gave lower readings than normal running temperature so I no longer worry about low speeds with (impossibly?) high loads for short periods.

Another topic of interest is my little CNC mill which has a 2 Pole 1Hp Electro Adda Compact Frame motor which a Siemens Micromaster 440 has been cheerfully running at 7000rpm for extended periods over a 3 year time span with no signs of any problems.

John S had 3Hp motors rewound for higher frequency use as router spindles and ran the standard rotors at 8000rpm without issues, I share his views on the chances of new, inverter rated, brand name motors exploding ;-)

My conclusions are that users should follow manufacturers instructions until they have enough experience and knowledge to do otherwise but that telling people what is or isn't possible should be based on empirical data, see above

 

[DJP]

Watching the responses to this thread has convinced me that for my needs a VFD has a primary purpose of producing 3 phase power from a single phase source in order to make use of industrial motors already in service. I can live with speed control as designed for the machine (belt/pulley changes) and if the VFD only provides 3 phase power and forward-stop-reverse function I'm happy.

 

[datosi81]

Watching the responses to this thread has convinced me that for my needs a VFD has a primary purpose of producing 3 phase power from a single phase source in order to make use of industrial motors already in service. I can live with speed control as designed for the machine (belt/pulley changes) and if the VFD only provides 3 phase power and forward-stop-reverse function I'm happy.

You hit it on the head! That’s exactly where I’m at with it in my mind also

 

[Wizard69]

I have a 1hp motor driven by an old LED display Siemens Micromaster Vector on my Myford Super 7, here's a video of it running you might like -

https://youtu.be/CgHcv8nk-gw

I might point out that a vector drive is a slightly different animal than a VFD. It is a topology specifically designed to over come the limitaitons of lower end drives.

That's turning Aluminium at 10Hz.
Primary drive belt is on High Speed, Final Drive belt is one down from top speed, this demonstration clearly shows how dramatically torque drops off at low speeds

Whilst you wouldn't run like this for extended periods without external cooling and a temperature sensor hooked up to the drive I've used Jog, which is set to 2Hz, for tapping M8 in 304 Stainless parts for significant batch sizes and since the duty cycle works out low regular checks on the motor temperature gave lower readings than normal running temperature so I no longer worry about low speeds with (impossibly?) high loads for short periods.

You will only have an issue if the motor starts to over heat. That said if people are really worried they can take off the supplied fan and add a fixed speed fan that can cool the motor at any speed.

Beyond that people must remember we are talking hobby machine tool usage (in most cases) and an occasional operation at high temp and very low speed won't hurt anything on a modern motor. I say modern motor here on purpose as there are real mechanical issues to consider with older motors.

Another topic of interest is my little CNC mill which has a 2 Pole 1Hp Electro Adda Compact Frame motor which a Siemens Micromaster 440 has been cheerfully running at 7000rpm for extended periods over a 3 year time span with no signs of any problems.

John S had 3Hp motors rewound for higher frequency use as router spindles and ran the standard rotors at 8000rpm without issues, I share his views on the chances of new, inverter rated, brand name motors exploding ;-)

I'm not sure which John S you are referring too but the discussion here was more about older motors if I understand the beginnings of this thread correctly. In any event I highly recommend referring to the manufactures data sheets for max rotor RPM on any motor you might implement. I can recall one manufacture having a family of motors all rated for fairly high speeds but there where a couple in the lineup with far lower max RPM ratings. Typo? Who knows but we where talking more than a couple of thousand RPM here.

My conclusions are that users should follow manufacturers instructions until they have enough experience and knowledge to do otherwise but that telling people what is or isn't possible should be based on empirical data, see above

Relying upon experience can be very questionable. I would rather stick with data sheet recommendations or is something really special needs to be done get the input of an applications engineer. Admittedly this is the way things are done at work (hopefully anyways) and prevents surprises down the road. The fact of the matter is most home users simply don't stress their machines in the same way industry does.

 

[Wizard69]

Watching the responses to this thread has convinced me that for my needs a VFD has a primary purpose of producing 3 phase power from a single phase source in order to make use of industrial motors already in service. I can live with speed control as designed for the machine (belt/pulley changes) and if the VFD only provides 3 phase power and forward-stop-reverse function I'm happy.

You do realize that variable speed will come to you via a potentiometer or a set of up and down arrows. The variable speed is a free benefit that will do know harm used properly and actually enhances your ability ot use the machine.

 

[DJP]

I'm OK with a pot for speed control as I have one on my mini-mill running a DC motor. My comment was simply that buying an older industrial machine with a 3 phase motor for use at home is beneficial if it can be powered with a VFD. The variable speed capability is still available in the original design of the machine and from the discussion it seems that burning up the motor and wasting the VFD investment is not worth the convenience of pot controlled speed. Adding a muffin fan to the motor makes sense but for my Bridgeport mill and hobby use I will leave it alone. I like belt speed control too as lower speed means higher torque.

I appreciate the sharing of information and assistance as it shows the true value of this website. No fake news here.

 

[Nick Hulme]

I would rather stick with data sheet recommendations.

There's nothing wrong with knowing your limitations and sticking to them ;-)