Gerry6309 wrote:01800s have dynamic braking
Actually 1500s, 1600s and 1700s have dynamic braking, 1800s have regenerative braking. The difference is that the current generated by the motors in the 1800s is pumped back into the third rail to be used elsewhere, while the current generated in the other cars is dissapated in resistors under the car. The two systems are operationally compatible. The differences lie in the control system, braking rates in the older cars are varied by changing the bias on the limit relay, which is controlled by the voltage on a train line wire. (Commonly these are 1 Power, 2 Accellerate, 3 Parrallel, 4 Forward, 5 Reverse, 6 Rate, 7 Reset - Hence the control cut-out is called a 7 point switch) In the 1800s the braking (all modes) are controlled by a digital signal - also carried on a train line wire. The two control systems are totally incompatible! The 1800s dont respond to simple on-offs or varying voltages and the other cars are ANALOG period! The 01800s may have air pressure carried through coupler hoses, but they don't respond to changes in pressure through relay valves. The braking is controlled through the P-wire only. BTW: SMEE doesn't require dynamic braking, the 1924 East Boston cars were converted to SMEE braking, but used air brakes only. SMEE stands for: Straight air, Motorman's valve, Electric control with Emergency features. The electric portion essentially measures the air pressure on the first car and matches it on the others.
The technology used in the older cars is fairly old, though low voltage circuitry and variable rates have been added since the early days of MU around 1900. Dynamic braking is triggered by loss of the power signal, and brake and accelleration rates increase as voltage on the rate wire drops. In coasting the rate is minimized, so the control follows the speed of the car. The ATO on the Red and Orange Lines simply turns these signals on and off based on the speed of the car. That's why the application is so heavy when the cars go from a 40 code to a 25 code and so forth.
To return to the original subject, the Type 7s and 8s both used similar digital control systems, so the main issue in making them compatible was adjusting rates to match and adding some multiplexed signals for the signs and ASA system to the Type 7. The AC or DC motors are operationally compatible, just don't try to put a Type 8 motor under a Type 7.
Oops, I got consfused ther, you're right 01400s, the old predecessor 06/700s had the SMEE braking, as well as the Toronto's TTC Gloucesters and their Montrealer M1s, in addition to the 1500s, 1600s and 1700s, the TTC H1, H2, H4, H5 and H6 also have dynamic braking, while their T1s, Scarborough RT ICTS and our 01800s have regenerative braking.
Also, I hope and wonder if Alstom will get to overhaul the 01700s, like WMATA and Chicago's Rapid Transit Cars, since they are good at rehabbing, hopefully they'll get the 01700s rebuild, unlike having it done here at Cabot with the 015-600s and 01400s from 1979-1987.
