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SP 5623
Electrical System

The 5623 has 3 distinct electrical systems. A set of 8, 8 volt batteries provide the 64 volt low voltage system, an alternator built in to the main generator provides the 3-phase AC needed to run the engine and traction motor cooling fans and the main generator supplies the high voltage for the traction motors. Note: References are occasionally made to a locomotive having a 72 or 74 volt low voltage system. In fact, when the engine is running, the charging voltage applied to the batteries, from a properly adjusted voltage regulator, is 72 volts DC, measured at the battery switch. The regulator output is actually set at 74 volts because of a dropping resistor between the generator and the batteries.

These are the battery compartments. There are 8 batteries in the locomotive, 4 on each side. Each battery is 28" long, 11" high and 18.5" deep. They weigh 418 pounds each and at this time in 1999, cost $3780 for a set. They are no fun to change but are removed by sliding them out the side of the box.

There are 3 electrical cabinets in the rear wall of the cab. Their contents do not match a stock GP9 because S.P. relocated almost everything during the GRIP rebuild. In the upper right corner of the center cabinet, there is a battery trickle charge that I installed. If the 5623 had dynamic brakes, the center cabinet would be a good deal more complicated.

On the opposite side of the wall from the photos above, are 3 cabinets containing the reverser (2nd photo), power contactors, transition circuits,miscellaneous relays and a LOT of wire. This is not a typical GP9 as S.P. had their own ideas on how to do things and where to put parts. However, the reverser and power contactors are in their stock locations.

The auxiliary generator serves the same function as the alternator on your car. It charges the batteries and more importantly, provides the electricity to operate all the systems on the vehicle while the engine is running. The 5623 has a 18KW version because of the steam generator. Gp9's are usually equipped with a 14KW unit. The main generator cooling blower is attached to the free end of the generator armature.

The alternator is 16 pole, 3 phase machine, built intgrally with the main generator. Its output varies with engine speed. The frequency is about 106 hz at 800 rpm and 36 hz at idle. The voltage is about 208 at 800 rpm and 75 at idle. It receives its excitation from the auxiliary generator through a set of slip rings on the free end of the main generator armature. Since the alternator is part of the generator, it is a bit hard to photograph, but this photo shows the location of the stator windings, next to the engine flywheel. Connection is made to the stator on the engineer's side, near the bottom of the generator.

The main generator is connected to the rear of the diesel engine by a flexible plate coupling, bolted to the engine flywheel. The generator is a DC machine with 12 brush holders, 6 negative and 6 positive. There is a winding built into the generator which, with battery voltage applied, causes the generator to revolve in the proper direction, cranking the diesel. The generator can put out over 1000 VDC and is capable of delivering about 6000 amps.

This is the view looking straight up into a traction motor with the lower inspection cover open. Two of the four brush holders can be seen. Each holder has 3 brushes. The GP9s were built with EMD model D37 motors but they were upgraded to the D77 specification during GRIP. This was done so that they were interchangeable between any S.P. locomotive application.

This collection of parts controls the air compressor. At the top left is the pressure sensitive switch that is adjusted to the compressor operating range. On the S.P., this was set to stop pumping at 140 pounds and start at 130 pounds. Some railroads use 120-130 pounds. These are the usual settings, as the FRA mandates that the main reservoir pressure shall be at least 15 pounds above the brake pipe pressure. In passenger service, the brake pipe is usually set to 110 pounds and thus, the 130/140 pound setting, while in freight service, the brake pipe is (west coast) normally 90 pounds.

The purpose of the load regulator is to control the loading on the diesel engine. It is nothing more than a hydraulically driven rheostat in the circuit between the batteries and the battery field in the main generator. The engine governor controls the rotary position of the rheostat based on the fuel demand of the engine. If the engine begins to require too much fuel for a given rpm, the governor will cause the load regulator to insert more resistance in the battery field, thus decreasing excitation. The governor will attempt to keep the load regulator at the highest excitation setting possible. The story is a whole lot more complicated that this, like what happens when the engine is at idle or during wheel slip or transition, but that's the general idea.

These are the rear traction motor blowers. The near photo is the engineer's side and the other, the fireman's side. In the near photo, the duct leading forward to the number 3 motor can be seen. These motors are 3 phase, 4 pole, 5 HP, 3100 RPM (at full engine speed) induction type. The front blowers are under the cab floor and a bit hard to photograph.

This is the underside of a radiator cooling fan. These motors are 3 phase, 8 pole, 9 HP, 1550 RPM (at full engine speed) induction motors. The fans are numbered 1,2,3 and 4 from the short hood of the locomotive. The fans do not all turn on at once but rather in a temperature controlled sequence. Number 1 turns on at 165 degrees, then #3 at 168, then #4 turns on and the rear shutters open at 171, and finally, the #2 fan turns on and the front shutters open at 180 degrees. The hot engine alarm will ring at about 208 degrees.

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