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[quote user="railroadjj"]Well, there are two different types.  Standard Range which gets you down to I believe 10 or 15, and then you have the extended ranged which will bring you to stop.[/quote]Noooo.  First, there are D.C. and A.C. locomotives.  D.C. locomotives have standard or extended range dynamic brakes.  A.C. do not have the feature as their dynamic brakes are controlled quite differently.  With D.C. locomotives dynamic brakes will not stop a train unless the train is going upgrade or is on perfectly level track, and no one cares within +/- a mile or so where the train comes to a stop.  A.C. locomotives can stop a train with DB alone, assuming the maximum braking effort provided by the locomotives is sufficient.  But the engineer still generally applies some train air or independent brakes for fine control as Wabash pointed out. For D.C. locomotives, as speed falls (the traction motor turns at a slower speed) the voltage falls, and thus braking effort diminishes (P = I2 * R).  Standard dynamic brakes have a designed speed at which maximum braking effort occurs; generally around 20 mph.  From 20 to 0 mph braking effort goes to zero proportionately.  Extended range uses contactors to short out sections of the dynamic brake grid step-wise in order to decrease the resistance of the grid down to about 7-8 mph.  Below that speed, dynamic braking effort goes to zero proportionagte with speed, just as with non-extended range dynamic brakes.  (There was apparently an option to obtain extended range brakes that would decrease the minimum speed for maximum effort to ~ 3-4 mph, but I don't if any railroad ever bought it; I've never seen it on a locomotive.)Scroll to the bottom of the page linked below for a graph that shows braking effort vs. speed for an A.C. locomotive and a D.C. locomotive equipped with extended range DB:http://www.unisa.edu.au/misg/2000/NRC/index.html S. Hadid
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