Friday, December 11, 2009

Let there be heat!

Last Saturday was cold, but the SN 1005 crew was toasty warm. It was time to test the 1005's heaters. They worked without a hitch! Although... when a heater is started up after 10 years... it does make some funny smells.

The thermostat hadn't quite been worked out yet. The circuit for the thermostat is just the type of ingenuity you saw in those early electrical systems. SN 1005 does not have batteries. How do you make a 600 volt thermostat without exposing the public to hazardous voltages? The 600 volt current path is a ladder, going through two large power resistors, through the heater contactor coil, to ground. That circuit, alone, would have the heat run all the time. The thermostat is wired "across" the heater contactor coil. When the heat should turn of, the thermostat closes contact, shunting the coil. This causes the contactor to drop out. There is an additional resistor through the thermostat circuit, so some current continues through the contactor coil. They also included a snubbing capacitor to reduce arcing in the thermostat.

The crew also beeped out the #1 and #2 traction motor leads on the carbody, comparing the leads and their markings to the drawing. These were checked against the two traction motors on the truck being serviced. Those traction motor leads are being repaired, given new sleeves and new cleat blocks (made of wood - seen here in the poorly lit paint shop), which guide the traction motor cables.

The conductor's bell was also tested. You can hear it after the whistle and horn.

(the embed caused problems on some computers. Go here to hear the sound.)

At this point, if the Westinghouse HL controls are operated, the reverser will throw and the switch groups will click and clack, transitioning through resistor grids and series/parallel. Here is the switch sequence. Notice that several contactors have exactly the same sequence, i.e. S1 is always thrown at the same time as S2. In some cases, two contactors were wired in parallel for increased current capacity.

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