# How low can you go.



## Suzuki4evr (Jul 27, 2021)

Hallo guys.

I know that a motor needs speed for the motor fan to keep it cool,but as you know your motor speed falls as you go down with the frequency to controle spindle on your mill using the vfd. Is there a dangerously low frequency you can run on a vfd. My motor runs at 50.00Hz at full tilt. I gather that at a short period of time it wil be ok if you run it at say 20.00Hz. So basically what is the lowest frequency and for how long can you run it at that frequency without risking motor damage?

-Michael-


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## Suzuki4evr (Jul 27, 2021)

Suzuki4evr said:


> spindle


Spindle speed


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## Superburban (Jul 27, 2021)

Most of my VFD equiped machines do not go slow long enough to have a great concern, so far just feeling the motor every so often has been ok. On my South Bend, when I get it on line, I plan to add a big muffin fan to blow into the motor. It will be setup to run anytime the motor is running. I just figure it will not hurt to run with the motor all the time, and is simple to wire a relay off the VFD to turn it on. Since the motor is not easy to get at, I have also been considering a temp gauge so I can monitor the temps.


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## pdentrem (Jul 27, 2021)

Depends on whether or not the motor is rated for invertor use. Can always add a separate fan to help cool the motor as stated above. 
Pierre


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## rabler (Jul 27, 2021)

Monitor the motor temperature.  As long as you can keep your hand on the motor continuously you have not pushed  it too hard.  Just be aware that it takes some time for heat to soak out to the case.


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## jwmay (Jul 27, 2021)

In school, they said don't run a vfd below half rated frequency. But I took it to mean we were protecting the VFD. Perhaps I misremember.


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## Suzuki4evr (Jul 27, 2021)

jwmay said:


> In school, they said don't run a vfd below half rated frequency. But I took it to mean we were protecting the VFD. Perhaps I misremember.


That is what I was told,not to go below 50%,and the motor temp was refured to. But if this is the case,then why does the vfd manual not mention this.


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## jmkasunich (Jul 27, 2021)

The VFD doesn't care until you start getting down to 1 or 2 Hertz.  If your motor is cooled by a shaft-mounted fan its cooling will suffer as you slow down.  Whether that matters depends on how heavily the motor is loaded.


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## graham-xrf (Jul 27, 2021)

Suzuki4evr said:


> Hallo guys.
> 
> I know that a motor needs speed for the motor fan to keep it cool,but as you know your motor speed falls as you go down with the frequency to controle spindle on your mill using the vfd. Is there a dangerously low frequency you can run on a vfd. My motor runs at 50.00Hz at full tilt. I gather that at a short period of time it wil be ok if you run it at say 20.00Hz. So basically what is the lowest frequency and for how long can you run it at that frequency without risking motor damage?
> 
> -Michael-


With an AC servomotor, I have taken it all the way to zero, acting as a big brake, holding up half a ton of satellite tracking dish in positional control. The AC motor had a smaller little motor mounted on it piggyback, and the task of the little motor was just to supply the cooling for the bigger one.

More general speed control "VFD" drives aimed at AC induction motors conversion might not be able to go all the way to stall, nor creep around with little movements at full torque. If you install a VFD, and the machine is an older one with gears or reduction pulley drives, it helps to use all the drive train in as low gear as possible, to let the motor run as fast as possible for a given spindle speed. Even with a 50Hz motor, you should be able to make the spindle roll around real slow. Cool the motor, even if you have to re-purpose a few computer fans to do it!


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## epanzella (Jul 27, 2021)

I run my 60hz Baldor 2hp from 30 to 120 hz without a prob.


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## mksj (Jul 27, 2021)

It depends on the type of motor, a TENV and TEBC are rated down to 0 speed, a TEFC which is the usual style of mill motor, around 15 Hz for any length of time. Below that point there is a higher chance of insufficient cooling. Depends a lot on the motor design, mass, type of load, duration, ambient temperature, etc. Since you loose Hp in a linear fashion below your base speed and you loose the mechanical advantage, turning down the VFD below 20 Hz you are operating with a significant reduction in power. So OK for light tapping/drilling, but less ideal if you are hogging out a lot pf metal.

Inverter/vector TENV motors and some TEFC motors often have temperature sensors in the motor that can be wired into the VFD to shut down if the motor overheats. A TENV typically barely gets warm at any speed, installed in manual mills and lathes.


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## Weldingrod1 (Jul 27, 2021)

Permanent magnet AC motors will happily do zero speed. Word of warning: many vfd's DO NOT like these motors!!! They act rather differently from squirrel cage! If you are asking for.much.torque you should add an external fan for really low speed operation.

Sent from my SM-G892A using Tapatalk


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## Suzuki4evr (Jul 28, 2021)

Thank you everyone. I think I am happy with all the responses. I am posting pics of the motor and vfd specifications for interest sake,both are brand new.







Thanks guys
Michael


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## plunger (Aug 8, 2021)

Is your 3 phase motor 380v or also 240v ?


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## Suzuki4evr (Aug 9, 2021)




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## plunger (Aug 9, 2021)

I read that your motor is 400v so in our world i would think that it is 380v. but most motors or many motors have the ability to be wired from star to delta. Your vfd is not clear in its output. At least i havent picked it up. Is it asingle phase  240v in 3ph  380v out or is it 240v in and 240v out. ? I see most bigger vendors in S Africa dont seem to supply the  3ph 380v out version.


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## jmkasunich (Aug 9, 2021)

plunger said:


> I read that your motor is 400v so in our world i would think that it is 380v. but most motors or many motors have the ability to be wired from star to delta. Your vfd is not clear in its output. At least i havent picked it up. Is it asingle phase  240v in 3ph  380v out or is it 240v in and 240v out. ? I see most bigger vendors in S Africa dont seem to supply the  3ph 380v out version.


I read the VFD nameplate as saying the output can be up to but not over the input voltage.  So with 240V in, you can get no more than 240V out.  As a former VFD design engineer, this is consistent with my experience.  The circuitry inside a VFD can only reduce the voltage, unless they add a special "voltage doubler" input circuit.  Traditionally this is only done for products that are intended to run on 120V single phase (mostly in the USA) and produce up to 240V output.  Not saying someone couldn't put a voltage doubling front-end on a 240V single phase drive so that it could make 400 (or even 480) volts out.  But I've never seen one.


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## plunger (Aug 9, 2021)

You can get 240v single phase in to  380v three phase out vfds.


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## Suzuki4evr (Aug 9, 2021)

plunger said:


> I read that your motor is 400v so in our world i would think that it is 380v. but most motors or many motors have the ability to be wired from star to delta. Your vfd is not clear in its output. At least i havent picked it up. Is it asingle phase  240v in 3ph  380v out or is it 240v in and 240v out. ? I see most bigger vendors in S Africa dont seem to supply the  3ph 380v out version.


It's single phase 220V in and 380V three phase out. The motor is configured in Delta.


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## mksj (Aug 9, 2021)

There is an outfit in the UK the sells step-up VFD's, that are 240V single phase in and 415V 3 phase out. Tend to be expensive, I have also seen some through Aliexpress, but do not know how well they work. The Alpha-Drive Micro VFD-A-E6-20022 above states that the voltage in (240V) = voltage out, so it will not output 380VAC 3 phase.




__





						Drives Direct - Digital Phase Converters - Home Page
					





					www.drivesdirect.co.uk


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## Suzuki4evr (Aug 10, 2021)

mksj said:


> There is an outfit in the UK the sells step-up VFD's, that are 240V single phase in and 415V 3 phase out. Tend to be expensive, I have also seen some through Aliexpress, but do not know how well they work. The Alpha-Drive Micro VFD-A-E6-20022 above states that the voltage in (240V) = voltage out, so it will not output 380VAC 3 phase.
> 
> 
> 
> ...


Ok so what are telling a me,a guy that is not so good with motors and electronic stuff,do my motor not run as a three phase motor even though it looks like it does or are you saying that I am not enjoying the power output of the 2.2kw three phase motor? Give it to me as if you are talking to a complete novice. Because I have a vfd that says 1PH Input and 3PH output 2.2kw and my my motor is 2.2kw 3PH running on 220v power.


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## plunger (Aug 10, 2021)

Being a complete novice myself and in the process of trying to buy a vfd myself ,i find it confusing. The motor tag shows its a 400v motor that is star wired . So I assume it would run on standerd 380v 3 ph in S Africa. Your vfd shows its single phase in at 240v and is three phase out . But is it 240v three phase or 380v three phase. If its 240v three phase would your motor not need to be able to run on 240v. ? I notice most of these motors have the ability to be wired either 240v or 380v but need to be changed from star to delta. I see you can buy either a 380v output or a 240v output vfd.
Where did you buy the vfd ?.I am in the market for one but have never bought off banggood or amazon before.


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## Suzuki4evr (Aug 10, 2021)

I am just as bad with this stuff and had a lot of help from my brother inlaw(electrical engineer) and guys on this site,so will lie to you if I want to help,struggling to help myself.  I got mine from Varispeed.


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## Suzuki4evr (Aug 11, 2021)

plunger said:


> But is it 240v three phase or 380v three phase.


Hi Plunger. The motor is re-configured to delta and 230V three phase. I don't understand how or why it works,but I know it does. There are much wizer members here who will be able to explain it better,but what I want to believe on how it works is that the Vfd convert the 380v three phase the motor needs into 230v three phase...........somehow. Like I said it is not my field of expertise, but all I know is that I have a three phase motor that works instead of my previous single phase motor. I just added a potentiometer to my VFD today and moved the VFD fom my machine to the wall. The guy who helped me alot is markba633csi. He helped me with all the rewiring and also the setting of the parameters, up to point where I think he suggested that I contact the guys from Varispeed. And I must say I could have saved Mark a lot of time by doing that sooner,because the guy just guided me over the phone. But if it wasn't for Mark,I don't know how I would have gotten to the finnish line on this. I hope you have someone who can help when you get your VFD. I am glad I did the conversion. Good luck to you. 

-Michael-


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