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I have an electronic clutch also called an electromagnetic clutch. It is a PTO clutch from a law mower if you're familiar.

The clutch is connected to a motor and a spool, the spool reels in a rope connected to a load. When the clutch is engaged the spool will spin with the motor, reel in the rope and lift the load. And when the clutch in disengaged the spool with free-spool, dropping the load with negligible resistance.

The goal is to engage the spool, lift a 1700 lb load a distance of 3 feet, and disengage the clutch so the load comes crashing down.

Stopping at a distance of 3 feet the easy part, I plan to simple turn off the motor which will stop the reeling motion of the spool.

Out of the box, the clutch is rated for 200 ft/lbs of torque.

Once the load exceeds 200 lbs, the clutch stays engaged but begins to slip resulting in the motor continuing to revolve but the spool does not and the load is no longer being moved.

How can I increase holding power, the magnetism of the clutch?

I'm aware that the magnetic force is dependent of 3 factors, 1. The number of turns in the coil. 2. The amount of current flowing through the coil. 3. The material used for the core.

Rough calculations tell me I need to increase the current by 3 times and the exponential power produced will be around 1800 lbs. Please verify this.

However, if I increase the current by a factor of 3, how do I know if the coil can handle that increase?

Thanks in advance for any help!

AndyT
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Alex Segovia
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1 Answers1

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As others have stated in the comments, exceeding the coil power will burn up the coil. There is also a finite amount of clutch pad area, and higher forces will wear it out exponentially quicker. You have some options:

  1. Larger Clutch - Buy a larger clutch that is rated for the torque. Vendors on Alibaba can be a great resource. The highest I found with a quick search was one with 1000Nm static torque.
  2. VFD Control - Since you are connecting to a motor already, just speed control that motor to stop and reverse with a VFD. Note that the VFD will need breaking resistors even if providing no resistance to the load to prevent it an over voltage error.
  3. Smaller Pulley - If your cable can handle a smaller bend radius, reduce the diameter of your pulley. This reduces the required torque and gives you a gear reduction without "gears".
  4. Block and Tackle - Similarly you can use pulleys to increase the force again reducing the required torque at the motor.
  5. Pneumatic Cylinder - Since you are only going up 3 feet, maybe consider abandoning the pulley idea altogether. Pneumatic cylinders can easily be sized to be within that distance and force, and unlike hydraulics they can move with very little resistance when vented to atmosphere.
  6. Electromagnet - Use the pulley or some other means to lift such as hydraulics, then use an electromagnet or set of electromagnets to quickly disengage the load. Then have an automated retract and reattach process.
ericnutsch
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