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Torque Controller


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#1 Guest__*

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Posted 28 March 2005 - 07:19 AM

Hi all,
In speed reduction mechanical gear box, the output torque is improved ( increased). For example If the speed reduction is 1:10, we can get the output torque increased by 10 times.

Now by using a electronic speed controller for speed reduction can we achieve the same torque improvement

#2 marke

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Posted 28 March 2005 - 10:29 AM

No, unfortunately, the thorque produced by the motor is a function of the flux in the iron. At rated speed and voltage, the flux in the iron is the maximum that the motor can stand long term.
As we reduce the frequency applied to the motor to reduce its speed, we must reduce the voltage applied to the motor so that the maximum flux is not exceeded. This results in the motor only being able to develop rated full speed torque at reduced speeds. In effect, the power rating of the motor reduces as the speed is reduced.
Below rated speed, AC induction motors can only deliver rated torque. Above rated speed, AC induction motors can deliver rated power.
Some vector drives can supply above rated torque in short bursts, but not continuously.

If you use a DC motor, you can get increasing torque as the motor reduces.

Best regards,

#3 Guest__*

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Posted 28 March 2005 - 11:04 AM

I hope that may be the one of the reason still engineers are forced to use gear boxes for both speed reduction and torque improvment.

#4 jraef

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Posted 29 March 2005 - 04:15 PM

Actually, VFDs provibe speed CONTROL, not just speed reduction. If reduction to a single speed is all you need, a gearbox or a change in a sheave or other mechanical devices is a better choice. The same is true for pumps and fans as well. If all you want is one lower speed, a two speed motor is probably a beter choice, but if you want flow CONTROL, a VFD is much better.
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