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#1 rotomoulder

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Posted 09 March 2011 - 08:44 AM

I have a small 3P motor which is controlled by a VSD. I have just applied DC heating to it at some 6% of its max operating current and the rotor "Rocks" back and forward by a very small amount ( a few degrees) and at the same time the rotor becomes difficult to turn by hand which is great for my application.
My question is, Is it acceptable to leave the motor in this condition for some time, say 20 mins on heat and then 3 mins on run and then back to 20 mins on heat throughout the day?
The application is a 6 pole motor into a 50/1 Gear box driving a turret very slowly via a 50:1 chain reduction which give lots of torque but little in the way of speed. When the turret stops physical locks are put into place to stop the turret turning but if I can also nearly lock the rotor then the process could be safer( The VSD is set to shear pin so that if the locks are forgotten the VSD trips out))

#2 jOmega

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Posted 10 March 2011 - 02:54 PM

QUOTE (rotomoulder @ Mar 9 2011, 02:44 AM) <{POST_SNAPBACK}>
I have a small 3P motor which is controlled by a VSD. I have just applied DC heating to it at some 6% of its max operating current and the rotor "Rocks" back and forward by a very small amount ( a few degrees) and at the same time the rotor becomes difficult to turn by hand which is great for my application.
My question is, Is it acceptable to leave the motor in this condition for some time, say 20 mins on heat and then 3 mins on run and then back to 20 mins on heat throughout the day?
The application is a 6 pole motor into a 50/1 Gear box driving a turret very slowly via a 50:1 chain reduction which give lots of torque but little in the way of speed. When the turret stops physical locks are put into place to stop the turret turning but if I can also nearly lock the rotor then the process could be safer( The VSD is set to shear pin so that if the locks are forgotten the VSD trips out))



The answer is dependent upon your ability to define the Thermal Duty Cycle. You will need to determine how much Heat is introduced into the motor by the DC Heating versus how much heat is removed by running the motor before the next application of DC Heating.

Not an easy task, as there are too many "unknowns".

Then there are the application and safety considerations.

DC Heating was never intended to be used as a "holding brake".

The motor would always have power applied even when it is at rest.
This is not a good practice as it has the potential to cause injury to personnel.

A much better solution, in our opinion, and one we have used in similar applications,
would be to replace the motor with a Mannesmann Demag KB Conical Brake Motor

See Link Below

The brake is integral to the rotor of the motor. Separate control of the brake is not required.
The brake operates from the power applied to the motor.
A splined coupling will be required between motor shaft and mechanical load; i.e., gear box; as
the rotor does slide in and out when power is applied and released. Movement of the rotor operates the brake.
Motor works with existing Inverter, but may need to dial-in some boost at zero speed.

Demag Conical Rotor Motor Type KB

You can also use a search engine such as Google and find additional information about the Demag motor.

Disclaimer: jOmega is not an agent for nor has any material, financial or commercial interest in Mannesmann Demag products.





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