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I have a 480v motor that is connected to an auger.

When the auger fills up, the torque from the motor continues to drive it and then just snaps the shaft clean in half.

I am looking to build something that decreases power as the amp draw increases. Hopefully preventing the snapping of another shaft.

I’m open to any thoughts and I’m pretty new to electronics.

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    \$\begingroup\$ I think it might be easier to use a smaller motor, a slipper clutch, or just loosen the belt (if it has one). I don't expect a fuse or breaker to be accurate enough. In any case, know how to detect when the overload device is working and shut it off immediately! \$\endgroup\$ – AaronD Aug 13 '18 at 22:27
  • \$\begingroup\$ That is odd. Most motors with such power have both speed and torque adjustments built into a controller made for that type of motor. I get the feeling you are missing that important item. \$\endgroup\$ – Sparky256 Aug 13 '18 at 22:32
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    \$\begingroup\$ While the other comments about a suitable control system are correct, a shear bolt in the driveline will prevent major damage : many agricultural things use shear bolts 2 maybe 3 as necessary to cope with straw choppers taking in branches for example... \$\endgroup\$ – Solar Mike Aug 13 '18 at 22:52
  • \$\begingroup\$ As mentioned above, just look ar references to slip clutch and sher pins: countrysidenetwork.com/daily/homesteading/… \$\endgroup\$ – DrMoishe Pippik Aug 13 '18 at 23:13
  • \$\begingroup\$ Have you ever dealt with closed-loop systems? This question is in dire need of it. \$\endgroup\$ – Harry Svensson Aug 13 '18 at 23:20
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If the motor does not already have an electronic speed controller, the only way to reduce the torque and speed is to add one. Assuming the motor is a three-phase induction motor, you need a variable frequency drive (VFD). The cost of a VFD will be significantly more than the cost of a motor.

Before you buy a VFD, you should determine if there is something else that needs attention.

  1. Determine if the augur filling up is a normal or abnormal condition.
  2. Determine if something other than just filling up is contributing to the problem and whether or not that is a normal condition.
  3. Determine if the augur is suited to the material and conditions.
  4. Determine if the motor and mechanical drive train is suitable for the augur, material and conditions.

If the condition that caused the shaft to break is something that happens only occasionally under abnormal conditions, a mechanical or electrical means of shutting down the motor and or disconnecting the drive train may be suitable.

Make a sketch of the equipment, motor, drive train, augur, infeed system, outfield system etc. Note down all of the relevant dimensions and ratings.

If there is a VFD, it should be simple to adjust the current or torque limit.

Note that limiting the motor torque will likely result in the motor stopping when the problematic condition occurs. Limiting the torque will reduce the speed, but it is not the nature of an auger to require significantly less torque to operate at a lower speed.

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    \$\begingroup\$ A VFD is a way. It is not the only way. Things like this existed for generations before those became practical. \$\endgroup\$ – Chris Stratton Aug 14 '18 at 0:28
  • \$\begingroup\$ I know about mechanical and electromechanical solutions, but I don't know another electronic solution that would provide continuous torque control for the existing motor. \$\endgroup\$ – Charles Cowie Aug 14 '18 at 0:40

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