Guardian Technologies 4389, 4456, 4390 LOW OIL Pressure Shutdown, High OIL Temperature Shutdown

GENERAL INFORMATION

PART 1

SECTION 1.5

ENGINE-GENERATOR PROTECTIVE DEVICES

GENERAL

Standby electric power generators will often run unattended for long periods of time. Such operating parameters as (a) engine oil pressure, (b) engine temperature, (c) engine operating speed, and (d) engine cranking and startup are not monitored by an operator during automatic operation. Because engine operation will not be monitored, the use of engine protective safety devices is required to prevent engine damage in the event of a problem.

Prepackaged generator engines mount several engine protective devices. These devices work in conjunction with a circuit board, to protect the engine against such operating faults as (a) low engine oil pressure, (b) high temperature, (c) overspeed, and (d) overcrank. On occurrence of any one or more of those operating faults, circuit board action will effect an engine shutdown.

LOW OIL PRESSURE SHUTDOWN:

See Figure 1. An oil pressure switch is mounted on the engine oil filter adapter. This switch has normally closed contacts that are held open by engine oil pressure during cranking and startup. Should oil pressure drop below approximately 10 psi, the switch contacts will close. On closure of the switch contacts, a Wire 86 circuit from the circuit board will be connected to ground. Circuit board action will then de- energize a "run relay" (on the circuit board). The run relay’s normally open contacts will then open and a 12 volts DC power supply to a Wire 14 circuit will then be terminated. This will result in closure of a fuel shutoff solenoid and loss of engine ignition.

HIGH OIL TEMPERATURE SHUTDOWN:

An oil temperature switch (Figure 1) is mounted on the engine block. The thermal switch has normally open contacts that will close if oil temperature should exceed approximately 284 F (140 C). This will result in the same action as a low oil pressure shutdown.

OVERSPEED SHUTDOWN:

During engine cranking and operation, the circuit board receives AC voltage and frequency signals from the generator engine run windings, via Wire 66A. Should the AC frequency exceed approximately 72Hz (4320 rpm), circuit board action will de-energize a "run relay" (mounted on the circuit board). The relay’s contacts will open, to terminate engine ignition and close a fuel shutoff solenoid. The engine will then shut down. This feature protects the engine-generator against damaging overspeeds.

NOTE: The circuit board also uses engine run winding output to terminate engine cranking at approximately 30 Hz (1800 rpm). In addition, the engine run winding output is used by the circuit board as an "engine running" signal The circuit board will not initiate transfer of electrical loads to the "Standby" source unless the engine is running at 30 Hz or

above.

Figure 1. Engine Protective Switches on an

Air-Cooled Engine

OVERCRANK SHUTDOWN:

Automatic engine cranking and startup normally occurs when the circuit board senses that utility source voltage has dropped below approximately 60 percent of its nominal rated voltage and remains at that low level longer than fifteen (15) seconds. At the end of fifteen (15) seconds, circuit board action will energize a crank relay and a run relay (both relays are on the circuit board). On closure of the crank relay contacts, circuit board action will deliver 12 volts DC to a starter contactor relay (SCR, for v-twin models) or a starter contactor (SC, for single cylinder models). The control contactor will energize and battery power will be delivered to the starter motor (SM). The engine will then crank.

During a manual startup (AUTO-OFF-MANUAL switch at MANUAL), action is the same as during an automatic start, except that cranking will begin immediately when the switch is set to MANUAL.

Circuit board action (during both a manual and an automatic start) will hold the crank relay energized for 15 seconds on. The relay will then de-energize for 15 seconds off. It will then energize for seven (7) seconds on and de-energize for seven (7) seconds off. It will repeat this same cycle for another 45 seconds.

If the engine has not started after approximately 90 seconds of these crank-rest cycles, cranking will automatically terminate and shutdown will occur. The circuit board uses AC signals from the stator engine run winding as an indication that the engine has started.

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