How to calculate for single to three phase

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biqut2

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It's been my experience that torque drops with lower rpms on a vfd. At least this is true with the 2.2kw 24000rpm motor on my router and the 3600rpm motor on my mill. Both are 3 phase, the former is 400hz and the later is 50hz.
 

lemelman

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It's been my experience that torque drops with lower rpms on a vfd. At least this is true with the 2.2kw 24000rpm motor on my router and the 3600rpm motor on my mill. Both are 3 phase, the former is 400hz and the later is 50hz.
Many people use a VFD to get a slower spindle speed without changing the gearing. Using a lower gear actually magnifies the available torque, but if the VFD is used in the expectation that it would behave in the same way as gearing, then it appears that the slower motor has reduced torque because it isn't magnified by the lower gear..
 

BobNZ

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What solution DC or VFD is most pleasant noise-wise?
It depends on what noise you wish to reduce. Constant fan hum can be a bit distracting and is unnecessary when the VFD is not driving a motor or is under very light load. The fan is for cooling so ambient air temperature must be taken into account when looking at modifying fan operation.
There are several options such as having a series of speed steps for the fan related to the need for cooling or the simplest one is to have an on / off arrangement with the fan being turned on as the heat sink becomes warm.
This utube video is one persons approach.


Electrical interference generated by VFD is another issue. Harmonics and radio frequency emissions ( RFI) can be a problem if other devices sensitive to these emissions are effected. There are solutions for most of these "problem" side effects of VFDs.

So it depends on what "noise" you need to reduce as to what measures may be needed.
 

Ken I

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I have found most single phase motors can be rewound to 3 phase and the number of active poles can be changed as well - just find a competent rewinder.

Further you can use a VFD to run the beans out of the motor - typically generating many multiples of the horsepower.

I do this all the time in my line of work (robotics) where I need much more power to weight ratios than are typically available from standard 1500 / 3000 rpm configuration squirrel cage motors.
(See attached article)
Most motors can be spun up to 3000 - 12000 rpm for commensurate winds and appropriate consideration to bearings. balance, cooling and other issues.

Most persons are going to chime in and tell you why not - but I am talking from real world practical application here.

Regards, Ken
 

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Niels Abildgaard

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I have found most single phase motors can be rewound to 3 phase and the number of active poles can be changed as well - just find a competent rewinder.

Further you can use a VFD to run the beans out of the motor - typically generating many multiples of the horsepower.

I do this all the time in my line of work (robotics) where I need much more power to weight ratios than are typically available from standard 1500 / 3000 rpm configuration squirrel cage motors.
(See attached article)
Most motors can be spun up to 3000 - 12000 rpm for commensurate winds and appropriate consideration to bearings. balance, cooling and other issues.

Most persons are going to chime in and tell you why not - but I am talking from real world practical application here.

Regards, Ken
Hello Ken

I have released a lot of inbuilt smoke from two old motors ,fooling around with a cheap inverter.
Your very well written paper has explained why I think.
It was a pleasure to read and thank You.

Kind regards

Niels
 

Wizard69

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A couple of things here.

1. Most motor manufactures these days publish max speed recommendations for current or recent motor models. So for newer motors you don’t have to guess about permissible speed ranges.

2. Further don’t assume every motor in a family has the same speed range ratting. Some variants will have substantially lower max permissible rotor speeds.

3. On rather older models motors I would be reluctant to go to a 120 HZ.

4. Don’t confuse power with torque. Torque is somewhat flat when the motor is driven by a VFD but that doesn’t mean you have power at low speeds. A belt or gear speed reduction is still important at lower speeds.

5. The other reason for a gear ratio between the motor and spindle is to keep motor RPM up so that you get a cooling effect from the fan.

6. All of the above implies simple low cost VFDs. Use a vector drive, a drive with RPM feedback or other advanced features (AC servos) and you end up with different performance characteristics.
 

ddmckee54

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At lower motor speeds, it's all about the heat. Most lower cost motors will recommend not to run the motor below 20-25% of rated motor speed when using a VFD. This is not due to the fact that the motor won't run at those low speeds, it's because the cooling fan will not be turning fast enough to keep the motor cool.

If you force cool the motor you can run at virtually any speed. As I sit here, I'm within a few hundred feet of about a dozen extrusion systems that run on VFD's. These are 300-600HP three phase motors with VFD's that will provide 100% rated torque at 0 RPM, and do that 24/7 as long as you want. The only thing that's special about these motors is that they have a forced air cooling jacket. Of course the forced air cooling blowers on these motors ALL have 5HP motors or above - and those cooling fans are running full speed all the time or the main motors DON'T run.

If you want to run the motor at low speed without forced cooling, then pay attention to the motor temperature. When the motor temperature reaches the point where you can't comfortably KEEP your hand on it for a few seconds, then it's time to take a break. Go have a cuppa, or a cool one or two, anything to let the motor cool off. Remember, every degree over 140°C that those windings experience will knock about 10% off the motors rated life.

Don
 

BobNZ

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Air flow though some motors is better than other and some motors are encased as protection in volatile environments, so rely on external fins for cooling. The field coils and the armature both heat while the case temperature is affected more by the field coils heating in the short time frame.

Some manufacturers raise the power rating of their motors by increasing the field coils capability which usually means the field windings warm more slowly, but the armature just works harder when the extra load is applied. It is more difficult to check the armature heating, and applying your hand to the outer case only gives an indication of total residual heating from both the field coils and the armature after air cooling has taken some heat away.

A wide safety margin is a wise precaution particularly if running lower than rated speed with a reduction of AC frequency down from the motors rating. Many VFDs do provide a meter option so current draw can be monitored.

Heavy work loads at low spindle speed require gearing and some common sense as to how a VFD is used to give speed flexibility .
 

abby

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I have bought 2 inverters from Gavin, both have failed after a few months of light use so I would not recommend him.
Dan.
 

abby

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For bigTrev

A BCA is a small jig borer with a rotary table , it's the machine on the left of the picture.
Dan.
 

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