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| Re: ''Oldest subway cars not being replaced afterall'' (1134379) | |||
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Re: ''Oldest subway cars not being replaced afterall'' |
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Posted by Bill West on Mon Jan 23 16:27:06 2012, in response to Re: ''Oldest subway cars not being replaced afterall'', posted by 3-9 on Mon Jan 23 15:04:02 2012. The M1’s were designed from the start for a higher acceleration rate. It needed more power than the existing 3rd rail system could supply so the voltage was increased to get closer to the needs. For the old cars however that didn’t change their designed current steps and thus acceleration rate.The designer’s chosen acceleration rate is measured by the motor current, and keeping up that current as the car accelerates determines the steps needed in the car’s control equipment. The voltage just changes the mph at which each resistor is cut out of the circuit. Changing the rate to match the new cars would require different taps on the accelerating resistors, maybe more contactors and possibly more current capacity in the wiring and parts. Complete replacement is often cheaper than modifying everything in place. You might even have to put bigger motors on. Bill |
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