Diagnosys: Auxiliary Power Unit (APU)

Auxiliary Power Unit Testing

The Auxiliary Power Unit converts third rail power to the DC and AC voltages required for each of the subsystems on the train. The APU typically contains a Low Voltage Power Supply (LVPS) and a single or multi phase Inverter. Diagnosys can provide a full load test solution for an entire APU or individual LRU testing for the LVPS or Inverter.

High voltage and/or high current testing of these subsystems requires specialized hardware and software that not only verifies functionality of the UUT but also provides the necessary safety for the operator. Diagnosys uses hardware controlled safety systems to prevent access to the lethal voltages and current required to test the APU and its associated LRUs.

The S500 BTE can be configured with the appropriate programmable input power and output load control to provide the automated test of the APU and all of its subsystems while protecting the user with safety interlocks and shields.

Diagnosys has provided automated full load testing on Auxiliary Power Systems from 12KW to 77KW. These S500 based systems incorporate the same user interface as all of our low voltage test systems with guided instructions for interconnects and proper operation of the UUT.


  • Automated test of Mass Transit Auxiliary Power Units
  • Automated fault identification
  • Safety interlocks and shields to protect the user and test equipment
  • Automatic test result logging
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