Dynamo and Regulator Test Rigs

Shown in these pictures are the two remaining functional test rigs. They are similar to one another but test the equipment from different makers, either the Wolverton type or Stone's Patent type.

The electricity to light the lamps is generated at a nominal voltage of 24 volts d.c. (direct current) by the dynamo shown at the bottom left.

The dynamo voltage is zero volts at rest and will increase directly with speed reaching 24 volts at a carriage speed of about 25 miles per hour and will continue to rise as speed increases.

Each carriage has its own dynamo which is belt driven from a pulley on one of the bogie axles. Here the dynamo will be driven in a similar manner by a variable speed motor, mounted beside the rig, controlled by the two red handwheels, operating the mechanism at the base of the test rig.

To control the dynamo voltage at just above the nominal 24 volts a regulator is required. This is the large black box that can be seen at the top of picture above. The regulator consists of a collection of coils, wire resistors and switches to achieve the voltage regulation and retain it at a steady level at all speeds above 25 miles per hour. Each carriage is fitted with a regulator.

When the dynamo is at rest the voltage required for the lamps is supplied by a bank of lead acid batteries which can just be seen at the rear of the test rig at the bottom right.

When the dynamo is running and reaches just above 24 volts the regulator will switch the load from the batteries to the dynamo and it will also allow the batteries to be recharged fully from the dynamo. Similarly, when the dynamo slows and its voltage drops below 24 volts the regulator will reconnect the load to the batteries.

To check the operation of the dynamo and regulator cannot be carried out on a moving carriage, thus it is essential for either item to be removed from the carriage and connected to the test rig via about 12 large cables for testing and calibration.

Notes: Malcolm Hanson
Photos: Colin Jenkins