Our interurban, built in 1912, has 5 Canadian GE resistance coils. They consist of grids of ordinary band iron folded back and forth. On the "A" end one (in our case the north end) which we are calling No. 1 resistance coil the binding posts receiving wire are attached on the first grid and the 5th grid. From what I have be told these are wired to the controller and allow the car to start slowly with this set only going up to the, say a certain notch. Thus, only these grids are in use to a predetermined certain speed and the remaining 13 grids in this coil are not used.
Can knowledgeable person comment: Are the remaining 13 grids in this resistance coil not used? Was this type of resistance coil built as a common type and could be set-up for individual preferences? (ie type of controller, motor, etc.)

A design for the electrical was different for virtually every car series and depended on HP, speeds, gearing, weight of the car, passenger loading, wheel diameter, etc, etc. Typically, the total resistance of the 'bank' was in series with two motors (on a four motor car) for the first 'point' of control. That wasted or dropped the voltage to a single motor to something in the range of 60-75 volts, providing for the first step of the operation from a standing start, to be relatively smooth and limit the loading on the motors. At the the next controller step, a differnt tap or connection to the resistance bank would result in less of the total being connected to the motors, maybe 120-150 volts to each motor. Being DC motors, they would then gain more speed.

What I am describing my be very simplified for an electric trolley using K controllers. But even there they have various combinations and numbers of control steps.

Typical resistance grids used in series to control the motor speeds had to withstand (often) hundreds of amps and were cast iron of significant cross section. There could be as few as two 'boxes' of these to as many as 8-12, under an interurban. There were literally as few as 100 grids to many more as their cumulative resistance needed to add up to perhaps four times the total resistance of the motor windings - armature plus field coils.

Evolution of controls often used low voltage master controllers in the cab setting contactors in a housing below the car floor. A band wound resistor is unlikely to be part of the control resistance to the motors. It simply would not take the perhaps hundreds of amps of current needed.

More likely what you are referring to would be part of an 'evolved' elecrto pneumatic system where you have a dropping resistor for the low voltage contactor current, a battery system backup, a wound resistor for headlight and dimming circuits, or any one of several outher auxiliary systems.

We would need more info on the car, type and number of motors, HP, etc to make a more educated guess. Where is the car? Has it been operated? What is the voltage? Have you tested the car? Have you traced all the wiring and created a schematic diagram?

You have to start somewhere, and some of what you asked will become apparent in the above exercise. But it is quite possible and recommended to test for continuity of each circuit, and then to check the safety of each circuit using a 'megger' for example, or other form of hi pot testing for the integrity of the insulation.

Been there, done that. It helps if someone on your team devotes the effort to understanding the circuits to get them right the first time, and to be able to better troubleshoot problems as they come up.

Bob Kutella

Your description sounds like General Electric type PR Rheostats. These are very old, not very common, and were usually used on two motor cars with 40 HP or less. Are these on car 1225? Maybe someone from Orange Empire could comment of the grids on this car.

The power resistors on old interurban cars were used to control the rate of acceleration. They have a very shout duty cycle, maybe two seconds per point. They are not suitable to be used for speed control. The running speeds for the car are determined by motor design, gearing, wheel diameter, etc.

Most cars start with all the power resistance in series with all the motors. The control system shunts out resistance as the controller is advanced. This arangement gets more complicated on newer cars. This system dissipates large amounts of power that comes off the resistors as heat. The reason for the short duty cycle is that this heat can melt the resistors of even set the car on fire if too much time is spent with the resistors in the circuit.

FVHRS:
See the private message posted for you.