DMR-600T Series 4

DMR-600T Series 4 in aircraft DC generator circuits

The DMR-600T Series 4 is an aircraft differential-minimum relay used in DC power supply systems. It controls connection of a generator or starter-generator to the aircraft bus and disconnects it when the generator can no longer safely feed the network. The relay is used with DC generators and starter-generators operating in aircraft electrical systems with a nominal 28.5 V network. In service, it is checked together with the generator, voltage regulator, power cables, cockpit controls, bus contactors and indication circuits.

Generator connection through DMR-600T Series 4

The relay closes the main circuit when generator voltage rises above the aircraft bus voltage by the required margin. This prevents early connection during generator run-up and avoids loading the source before it is ready. After connection, the relay carries the main generator current through its power contacts. On installations using starter-generators such as GS-18TO, the DMR-600T Series 4 forms part of the generator operating circuit together with the RN-180 voltage regulator and the DC distribution system. The relay itself does not regulate voltage; it switches and protects the connection to the bus.

Reverse current and polarity protection in DMR-600T Series 4

One of the main functions of the DMR-600T Series 4 is reverse current protection. If generator voltage drops below the bus voltage and current starts flowing back from the aircraft network into the generator, the relay opens the circuit. This prevents the generator from operating as an unwanted motor load. The relay also blocks incorrect connection in case of reverse polarity. In some aircraft schemes, the unit can support disconnection when the power lead between the generator and relay is damaged, depending on the external wiring used on the aircraft.

Remote control and indication with DMR-600T Series 4

The DMR-600T Series 4 supports automatic operation and also allows remote manual control from the cockpit, if this function is provided in the aircraft circuit. The crew can switch the generator connection according to the operating procedure, while the relay still performs its protective functions. The unit can also provide a signal for cockpit indication, showing whether the generator is connected to the common DC bus. During troubleshooting, indication faults should be separated from power contact faults, since lamp circuits, control wiring and relay operation are different parts of the same system.

Identification and ordering of DMR-600T Series 4

Before ordering a DMR-600T Series 4 relay, the exact series and marking should be checked against the aircraft parts catalog, wiring diagram, or product passport. The letter “T” indicates heat-resistant execution, and the series number matters for interchangeability. A visually similar relay may not match the required aircraft circuit if the terminal layout, control circuit, or protection settings differ. The product is also known under alternative designations DMR-600T Series 4 and ДМР-600Т серия 4.

Product Type: Differential-minimum relay / aircraft DC generator switching relay
Function: Automatic connection and disconnection of DC generators and starter-generators from the aircraft bus
Application / Where Used: Aircraft DC power supply systems
System / Installation Area: Generator feeder / DC bus connection and protection circuit
Compatible Aircraft / Equipment: Aircraft DC generator and starter-generator installations up to 18 kW, including systems using GS-18TO type starter-generators where applicable
Associated Equipment: DC generator or starter-generator; RN-180 voltage regulator; cockpit control and indication circuits
Rated Network Voltage: 27 V control and network circuit
Operating Voltage Range: 16 to 30 V DC
Aircraft Bus Voltage: 28.5 V DC nominal
Rated Main Contact Current: 600 A
Current Type: DC
Operating Mode: Continuous
Execution: Heat-resistant version, “T” designation
Functions: Automatic generator connection; reverse current protection; reverse polarity blocking; remote control; status indication; disconnection on power lead damage when supported by external circuit
Technical Documentation: Product passport, aircraft electrical system documentation, wiring diagram for specific aircraft type

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