# Low power - motor or VFD?



## datosi81 (Mar 10, 2018)

Managed to get the SAIMP mill situated where I want in the garage finally and Hooked up the VFD and had the motor spinning as expected on the bench.

Earlier today I went to reinstall the motor on the head and get the pulley setup etc.  after getting it hooked up and the belt on, the motor wouldnt spin regardless of frequency.  I pulled the motor back off and bench tested it.  With no load on it, the motor seemingly responds as expected related to the frequency.  I tried grabbing the shaft from a standstill and powered it up and was able to hold the  shaft still with almost zero effort.  I understand the motor may lack torque at lower frequencies but this seems like a real issue.  Im wondering if the motor is bad since I never ran it before to test it.  Or is my cheap eBay VFD bad?  Or am I using the VFD wrong and there is some setting I dont know about that needs adjusting?  The motor is labeled 1hp 1750rpm 3 phase.  My VFD is powered by a 20amp 220v single phase line, outputting (hopefully) 220v 3 phase.  

I have worked as an electrician many years ago for several years but admittedly never really did much with 3 phase, so my knowledge on that subject is just what Ive learned online.  My understanding is it doesnt matter what phase is wired to what wire on the motor, but that doesnt mean Im correct lol.  Or perhaps there is a setting in the VFD that needs to be changed.  Im leaning toward the motor simply being weak/worn.  Any advice is appreciated


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## Nick Hulme (Mar 10, 2018)

Is the motor dual voltage? if not it's likely you're running it at half it's rated voltage. 
If it is dual voltage how is it wired, Star or Delta? 
Your VFD should always be set up with the data from the motor plate entered in the appropriate parameter settings. 
Make, model and data plate photos always help and save others who would like to help guessing the missing info, 
Regards, 
Nick


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## datosi81 (Mar 11, 2018)

View attachment IMG_1971.jpg
View attachment IMG_1972.jpg


I double checked it and it is wired for low voltage with wires 4, 5, and 6 tied together.


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## Nick Hulme (Mar 11, 2018)

VFD make and model? 
How did you set it up? 
BTW I have a lathe, drill press, two mills and a tool and cutter grinder running on 3 phase motors with VFDs, 3 Siemens, 1 Hitachi and an Omron, the first thing I do is download the manual for the VFD, the second thing I do is buy the VFD ;-)


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## Wizard69 (Mar 11, 2018)

It is never a good idea to grab a hold of a motor shaft no matter how low the apparent torque.   If the motor decides to startup it will tear your hand to pieces before you even realize it.    If you want to see if a motor is developing torque us a block of wood to rub against the shaft.    I don't want to sound like I'm preaching but safety is often overlooked at home.

The second thing to do is to set the drive up to run at the motors standard parameters, most likely 240 VAC @ 60 HZ.   If no torque is developed at this value then I would make sure he drive is set up right first and second make sure the motor is not running single phase


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## xpylonracer (Mar 12, 2018)

You say you have linked 4,5&6 but have you also linked 1-7, 2-8, 3-9 and supply in at 1,2,3 ?

Emgee


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## datosi81 (Mar 12, 2018)

Xpylonracer - yes, that is how I have it wired. Sorry I should have specified.

The vfd is a generic eBay HY or huanyang I believe is the spelling, 1.5kw.  The instructions are very basic.  Some of the literature Im finding online show parameters for most vfd into the 140s or 150s.  The instructions with mine only go up to the 30s.  So Im not sure if the parameters are the same meaning Pn003 is the same as Pn003 from a booklet I find online.


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## Aries37 (Mar 12, 2018)

I think more diagnostics are neede here to find your exact problem. If you have the motor leads connected together as shown on the motor nameplate and those resulting three leads connected to the VFD per the instructions and it still doesnt run correctly, take the motor to your local motor shop and have them megger the windings. Thats a high resistance test applied to the windings that will determine if their is moisture plus insulation condition, etc. If it passes that test have them run it on true 3 phase power. If it passes this test you know the motor is good. Then youll know your problem is with your VFD or the wiring to it. I would not purchase used electrical components like this from eBay that often come without complete instructions or a warranty.  Purchase from a reliable distributor that provides warranty and tech services should they be needed. I have several VFDs that have been running in my shop for many years with zero problems and all purchased from the same vendor. I can supply the name should you choose to proceed further.


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## datosi81 (Mar 12, 2018)

Thanks for the feedback.  The vfd is brand new, its just the instructions are limited, offering info on the first 30 or so parameters for some reason.

I agree I need to get the motor tested.  Ill have to find a motor shop in the area.  I think if nothing else, as you suggested, hooking it up to true 3 phase would tell the story.  

If it ends up bad Ill need to decide if I should get another 3 phase or just pick up a single phase and rely more on belt changes...it seems the price difference isnt that significant.


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## Aries37 (Mar 12, 2018)

The nameplate on your motor states a 182 frame size plus it appears to be totally enclosed as well. That style in a 1 hp tells me that it is probably special for your machine as most replacement standard 1 hp motors do not come in that size frame. Keep in mind that the frame size determines all critical dimensions like shaft size, mounting hole dimensions, shaft height center and other critical info. 
You can have your motor re wound if it does not check out. Re winds are expensive due to nigh copper prices, but in the case of a special mounting its the best way to go. Also keep in mind that some replacement motors are not VFD &#8220;friendly&#8221; which means they are not wound with the correct wire and insulation to withstand the abuse the VFD imposes on the windings. Your existing motor is definitely one of the old ones with lots of iron, heavy construction, wiring and bearings that will operate without problems.


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## datosi81 (Mar 12, 2018)

Yeah I dont know how old it is, but it sure is heavy!  Id guess approaching 100lbs which seems like a lot of weight for a 1hp motor.  I know its definitely not the original motor as there is a funky adapter plate someone attached to it to get it to bolt to the machine View attachment IMG_1983.jpg


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## Aries37 (Mar 12, 2018)

I&#8217;ve seen this setup before. Using a non-standard motor for a mill, then modifying it by adapting a flange plate to mount it. In most cases it can be done, so at this point I would proceed to get the motor checked out at a motor shop. With that diagnosis you can decide the next step. Your motor was built by Louis Allis, no longer in business, but well known for quality and longevity even if overloaded. The weight is due to an all cast iron frame, heavy stator laminations and a well designed and built rotor assembly. Keep us posted on your results.


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## Nick Hulme (Mar 15, 2018)

Not all old 3 phase motors work properly with VFDs, the gear motor that came on my on my Rapidor Manchester power hacksaw wasn't compatible with a VFD, it turned but just not with the right speed or torque, the 3 phase 2 speed motor that came on my FB-2 mill head just generated some smoke  
Fit a nice modern flange mount motor and dump that Hunk-O-Junk!


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## datosi81 (Mar 15, 2018)

I contacted a reputable motor service/dealer in my area and spoke at length with the head technician.  He said I could bring it in and test it, but, to Nicks point, he feels confident its not compatible with the vfd and estimated the motor to be late 60s vintage at the youngest, if not older.  So now Im kicking around different ideas on motors.  I already bought the vfd so I might as well get a 3 phase.  

Another point the tech made is that he feels the vfd is probably too small for anything other than 1hp-ish.  I told him the vfd I bought is rated 1.5kw so I felt it should be good to 2hp but he said the rating is likely optimistic, plus since the vfd is single phase in, 3 phase out, its rating is probably even lower, being rated for 1.5kw with 3 phase in and out.

So I gotta figure out in the next few days what Im gonna do.  I am supposed to go look at a lathe in a few days that is 3 phase, so I could be in the same boat there.  But Im thinking if that motor is small enough, and new enough, I may be able to utilize the current vfd for that if it works out and just get a larger one for whatever motor the mill ends up with.


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## Aries37 (Mar 16, 2018)

I would get the motor checked out, then youll know if its OK. On the VFD issues, Im using several of them on old frame motors for years with zero problems. I use GS 2 AC micro drives purchased from automation direct.com.
My mill is a Lagun, many years old with a 2hp 3 phase motor. The drive Im using is rated at 230 volts single phase input, 230 volt 3 phase output. This drive is rated at .5 to 3 hp. Any motor over 3 hp requires 3 phase input power. So in that application your source would need to be true 3 phase or else a rotary generator. Static type converters are some times problematic and not recommended for a VFD drive setup. Also Im using input and output load reactors which are very important for operating older motors not rated for VFD use. All of this is installed in a control cabinet with proper line side fuses, etc. One of the nice features about this brand of drive is that the control faceplate is detachable with a proprietary cable so you can mount it conveniently on your lathe or mill. Another crucial point here is proper size wiring to and from the VFD. Long runs have voltage drops and therefore I typically go one size bigger on wire size than specified. Another issue is that torque ratings drop off considerably when the motor is operated at low rpms. In this case simply changing belts to a different pulley ratio solves that problem. Finally, there are a lot of design parameters that go into selecting and wiring up a VFD for correct operation.


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## Nick Hulme (Mar 16, 2018)

datosi81 said:


> Another point the tech made is that he feels the vfd is probably too small for anything other than 1hp-ish.  I told him the vfd I bought is rated 1.5kw so I felt it should be good to 2hp but he said the rating is likely optimistic, plus since the vfd is single phase in, 3 phase out, its rating is probably even lower, being rated for 1.5kw with 3 phase in and out.



All that might be true for "Unknown Warrior" brands from the far east, my Siemens, Mitsibushi, Omron and ABB drives are all good for at least their plated ratings, even in adverse applications. 
Two old 1hp Siemens Vector Drives I use on my lathe and power hacksaw have been continuously powered and in use for 15 years or so and were ex-industrial second hand units when I bought them ;-)


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## Wizard69 (Mar 16, 2018)

datosi81 said:


> I contacted a reputable motor service/dealer in my area and spoke at length with the head technician.  He said I could bring it in and test it, but, to Nicks point, he feels confident it&#8217;s not compatible with the vfd and estimated the motor to be late 60&#8217;s vintage at the youngest, if not older.  So now I&#8217;m kicking around different ideas on motors.  I already bought the vfd so I might as well get a 3 phase.


VFD's and 3 phase motors are probably one of the best improvements one can make to a machine tool for the money involved.   Variable speed is very useful and the other features modern drives have like soft start can lead to longer machine life.


> Another point the tech made is that he feels the vfd is probably too small for anything other than 1hp-ish.  I told him the vfd I bought is rated 1.5kw so I felt it should be good to 2hp but he said the rating is likely optimistic, plus since the vfd is single phase in, 3 phase out, its rating is probably even lower, being rated for 1.5kw with 3 phase in and out.


I'm going to suggest that the tech is full of crap.   Unless the manufacture is engaged in fraud it should be able to do what is says on the spec sheet.

You will see drive derating when you try to run a 3 phase in drive on single phase input.   This can happen with a combination of factors but primarily involves the rectifier on the input side of the VFD.   It is completely possible for  a 3 phase drive to have a bridge rectifier that is sized for 3 phase in but can't handle the current demands for single phase in.   An applications engineer can usually help with finding a drive that can run properly on single phase in.

These days though single phase 'in' is so popular that most drives under 5 HP rating have specs for operation on single phase.  The ratings are accurate with most manufactures, they pretty much have to be for liability reasons.


> So I gotta figure out in the next few days what I&#8217;m gonna do.  I am supposed to go look at a lathe in a few days that is 3 phase, so I could be in the same boat there.  But I&#8217;m thinking if that motor is small enough, and new enough, I may be able to utilize the current vfd for that if it works out and just get a larger one for whatever motor the mill ends up with.



Speaking of larger motors if you do re-motor and go the VFD route it is usually a good idea to uprate the motor a bit.   The reason is pretty simple as you vary the motors RPM the ability for that motor to produce power and lower rpm's GOES DOWN!   Thus going with a larger motors, for example a 3 HP in place of a 1 HP,  gives you more useful torque over a wider range of  speeds.

In any event I come back to the idea that you must have something wrong someplace.   If you set the drive to 60 hz the motor should perform in a way similar to across the line operation.   After all (assuming a 60 Hz country here) the operating conditions are the same.   As such I'd review your drive settings again.


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## datosi81 (Mar 16, 2018)

USA here, PA to be exact.  So yeah, 60hz.

If I had to do it over again I would have got a larger VFD to begin with.  Even if the 1.5kw I have is sufficient for a 2hp motor, I would likely get a 3 hp replacement.  I dont think returning it is an option as I stupidly tossed the box and the seller on eBay vanished.  When I go back into my purchases, that item is blank, so who knows?

I do tend to agree something is wrong.  The tech seemed knowledgeable but I dont really buy that the older motor just wont work.  I would think if there was a downside to a vfd on an old motor itd manifest as possibly shortened life, not it not working altogether.

I also agree the vfd settings could be off. It seems my instructions dont have all the parameters listed though and that is part of the problem.  My thought is, and if Im using the wrong terms forgive me but hopefully you guys know what I mean, the ramp up time is the issue. If there is a way to set the vfd almost like it were connected on a regular 3 phase with a contractor switch, I think the motor would be making the torque needed to get going with load on it.  Its almost like it makes next to zero torque starting and ramps up, which I get the reason for that, but to an extreme that stalls the motor with the slightest of loads, preventing it from ramping and ever getting to a usable torque.  Hopefully that makes sense.

Im also gonna make another thread about the lathe I looked at today....limited info on it online so it could answer some questions about what to do on the vfd front with the mill.


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## Aries37 (Mar 17, 2018)

datosi81 said:


> USA here, PA to be exact.  So yeah, 60hz.
> 
> If I had to do it over again I would have got a larger VFD to begin with.  Even if the 1.5kw I have is sufficient for a 2hp motor, I would likely get a 3 hp replacement.  I dont think returning it is an option as I stupidly tossed the box and the seller on eBay vanished.  When I go back into my purchases, that item is blank, so who knows?
> 
> ...



Ill jump back into this problem again and recommend that you get the motor tested at your local motor shop. If its OK then you can deal with the VFD and wiring. Ive done lots of VFD work and can tell you that most older motors work the best with no problems, if installed correctly. That includes the wiring to and from the VFD and the correct VFD selection. Most VFDs allow for a gentle ramp up to full speed along with dynamic braking so you can bring the machine to a quick stop. Without complete instructions from the manual, its probably impossible to get the parameters correct. Again my reference to purchasing from a distributor that can size a unit to fit your application plus offering tech services should they be needed.


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## MachineTom (Mar 18, 2018)

I agree you likely have a wiring issue. Start at the beginning, with voltmeter, is there 220 at the input terminals, hooked correctly. next while running on the bench output voltage 220, each wire to the correct connection on the motor, remove each wire nut and check the wire conductor is wound with the others. I have had the conductors slide back when installing the nut, losing contact and driving me nuts.

Recheck the pairing of the wires, note 2, 7, 1 are sometimes misread  leading to issues. lastly the parameters, is the FLA parameter set for a 1hp motor, is the output voltage selected


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## Aries37 (Mar 18, 2018)

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.


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## datosi81 (Mar 19, 2018)

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


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## Nick Hulme (Mar 19, 2018)

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


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## Herbiev (Mar 19, 2018)

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.


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## datosi81 (Mar 19, 2018)

Herbiev said:


> 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]


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## Aries37 (Mar 19, 2018)

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.


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## datosi81 (Mar 20, 2018)

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?


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## Aries37 (Mar 20, 2018)

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.


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## datosi81 (Mar 20, 2018)

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.


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## Wizard69 (Mar 22, 2018)

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.


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## Aries37 (Mar 22, 2018)

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.


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## ddmckee54 (Mar 23, 2018)

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


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## Aries37 (Mar 23, 2018)

Don, you are absolutely correct on what you stated. I&#8217;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 &#8220;megged&#8221; at the local motor shop.


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## Nick Hulme (Mar 24, 2018)

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


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## DJP (Mar 24, 2018)

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.


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## datosi81 (Mar 24, 2018)

DJP said:


> 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


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## Wizard69 (Mar 24, 2018)

Nick Hulme said:


> 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.


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## Wizard69 (Mar 24, 2018)

DJP said:


> 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.


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## DJP (Mar 24, 2018)

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.


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## Nick Hulme (Mar 25, 2018)

Wizard69 said:


> I would rather stick with data sheet recommendations.



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


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## BillH (Mar 29, 2018)

I run my Bridgeport pancake motor between ~20 to 120 hz. I have zero issues, but again, it doesnt run for any real amount of time in the home shop environment. Dont be afraid to take advantage of that speed control.


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