Converting amp readings to torque at stall

[Tucker4740]

Hi all,

I currently service dragline brakes. Our customers test these brake systems to see if they meet their standards after prolonged use. When on site they test the torque produced from the brakes by seeing how much amperage is required to break the stall of the motor with the brakes at max clamping force.

I'm wanting to convert this value to a motor torque and hence braking force so i can see how far off our brakes are under specification. I have attached a graph from GE re this motor:

MDP82E, Shunt Wound, 1300HP, 700RPM, 475 Volts, 2200 Amps.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1568674027/tips/240D1S1_ldzdgk.pdf[/url]

 

[7anoter4]

The torque is the product of current by a constant kT depending on the field current.
From the attached graph [in my opinion the number on the down line has to be the armature current] for I=2200 A and field current of 40 A [72 V] the torque is 10000 lb.ft [approx.]. Then kT for 72V field supply voltage is kT=10000/2200=4.545 lb.ft/A
For I=1000 A and field current of 40 A [72 V] the torque is 4.545*1000=4545 lb.ft
Follow the lines on the right side of the graph for other field supply voltages