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| Re: train with mechanical problems (606908) | |||
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Re: train with mechanical problems |
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Posted by Train Dude on Thu Apr 24 21:32:47 2008, in response to Re: train with mechanical problems, posted by trainsarefun on Thu Apr 24 21:03:24 2008. To put it very simply, cars with dynamic braking never truly coast. When in coast position, the car is actually set up for dynamic brake but with enough resistance in the circuit to produce minimal retardation. The braking efort is then increased by stepping resistance out of the circuit.In the power modes, it's not as simple. (But to over-simplify) In the first & 2nd points of power the 4 traction motors ae connected in series - at first with maximum resistance. The resistance is stepped out, as the logic tries to maintain specific currents (by sending run signals to a motor that rotates a cam that steps out grid elements). In the 3rd point of power, the motors of the same truck remain in series but the two trucks are hooked up in parallel, doubling the effective voltage each motor sees. Other factors such as counter EMF and field shunting also come into play but would likely confuse things here. Suffice it to say that a train may begin in 3rd point at 475 amps (per leg) at start-up but will drop to less than 1/2 that once the train is up to speed. |
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