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For fully automatic operation Polar has selected Murphy Controls to provide programmable operation and remote control. There are two controller models to choose from, Models 447 and 547. The basic difference between the two is that the 547 has both an RS 232 and RS 485 communications ports for remote monitoring and the 447 is limited to an RS 485 port.

For standby operation there are two operational modes that a D.C. generator can be configured for, the first is to have the generator to remain continuously on during the utility outage, and the second is to have the generator cycle on/off during the power outage. The second method requires a larger battery bank and is recommended for sites that experience long and frequent power outages.

There are two configurations that can be used to cause the generator to start after loss of utility power, one is to start based on sensing the loss of (AC) utility power and the other is sensing a low voltage condition on the load battery.

The battery voltage and current monitoring method is used for applications where the generator cycled on/off based on battery’s state of charge. The goal is to reduce engine runtime for lower maintenance and conservation of fuel.

The following describes a typical operation of a complete system with a battery bank, load, Polar generator, and a primary or secondary source of power:

The generator stop/start cycle is configured by the user and operates on sensing changes in the battery voltage, current demand, and timed sequences.

As the battery discharges (powering the load) it will drop in voltage, when the preset lower voltage set-point is reached the controls automatically begin the start sequence.

First the fan operates to purge any propane gas from the enclosure before engine starts (or starts a glow plug for a diesel engine).

After an adjustable run duration the fan stops and the engine’s starter cranks. If engine fails to start it rests for a programmable period of time. The fan purge (or glow plug) starts again, followed by the engine cranking.

After starting, the engine warms up for a preset period of time before the voltage regulator is switched on and alternator produces full power. This feature reduces engine wear and helps prevent the engine from stalling.

The power delivered by the generator will be dependent on the battery resistance (state of charge) and the load (resistance) demand. Adjusting the voltage output and current limit potentiometers on the Model 710 Voltage Regulator can control charging current into the battery.

The generator will continue to supply power until the battery reaches an upper voltage set point and a low current threshold. The current will drop as the battery increases in its state of charge or when a secondary source of power such a wind generator, solar photovoltaic array, or a rectifiers/battery charger come on to share the load and battery charge.

Shutdown sequence: after the battery reaches its high voltage and the current demand drops off, there is a programmable time delay before shutdown. This delay timer reduces generator short cycling. The model 547 controller has the option to let the cooling fan to continue to operate (to cool down the engine, enclosure, etc.) for preset time duration.

After the shutdown sequence is completed, the generator is now ready to cycle again.

Murphy controllers monitor and can report remotely the following operating parameters in order to shut down the system at the earliest sign of a problem (system configurations will vary the monitoring options):

• Fuel Pressure
• Oil pressure
• Oil temperature
• Water temperature
• Engine RPM
• Load battery voltage
• Starting battery voltage
• Alternator Output current
• Ambient air temperature

The Murphy controls can be configured for remote start/stop though a single pair of contact closures. The user’s SCADA or RTU controls (typical of telecommunications applications) can control the generator for routine exorcise and special functions. However, the best method of start/stop control and monitoring is via the RS 232 port using the Model 547 controller. Remote control and monitoring is especially advantageous during foul weather as it may save a trip by a service technician. In remote areas, during foul weather, a service call can cost thousands of dollars in travel expenses.

Starting Battery System

The starting system can be configured to use either one battery, the load battery, or use two batteries one for the load and the second for starting. A separate starting battery will require a dedicated charger (see Model 9600 Battery Charger) to provide power to the controller while the generator is not running. In addition to the energy required for powering the controls during standby operation, the battery has a natural tendency to discharge itself.

While the engine is running the generator charges the battery and powers the auxiliary loads. The auxiliary loads consists of fuel valves, pumps, fans, control relays.

Murphy Model 447

Murphy Model 547

Voltage Regulator Model 710

Battery Charger Model 9600