Yes Siemens Desiros, the "power hungry lardbutts", which consume so much extra juice that Railtrack Southern Zone had to put in a £1 billion (2.1 billion USD) power upgrade.
No sarcasm. Efficiency is a slippery idea in this context. The old trains were built in the 1960s, but the design was old fashioned even then. DC motors (with commutators & brushes), motor control was by resistances switched in and out by mechanical contactors operated by a camshaft driven by an oil motor. So great complication. The contactors needed tender care and adjustment from skilled workers to work properly. The drivers could tell from the performance if a skilled guy or a new guy had set them. The brushes on the motors needed replacing every so many thousand miles, the motors needed removing and reconditioning every so often. But if all this was done right they would last 100,000 miles between failures. All this maintenance meant that to provide 200 trains in daily service you needed a fleet of 210 because 10 would be in the workshop at any time. The design of the body was very flimsy. It was a sturdy chassis with a sheet metal box on top. The coaches would break up in a crash and the underframe would spear into the coach in front. There was a horrific crash at Clapham in 1988 where 35 people died. The new trains use solid state electronics. Three phase drive to brushless motors. Sturdy integral construction. Much lower maintenance, so a smaller fleet to provide the same level of service. But the three phase drive and the 1 MW airconditioning load means they take more power, for longer, and the substations heated up too much. On balance they are better trains in every way, but I am nostalgic for the old trains of my childhood...
