CIRRUS

AIRPLANE MAINTENANCE MANUAL

MODEL SR22

ELECTRICAL POWER 1. GENERAL This chapter contains information on DC Generation, External Power, and Electrical Load Distribution. The airplane is equipped with a two-alternator, two-battery, 28-volt direct current (VDC) electrical system designed to reduce the risk of electrical system faults. The system provides uninterrupted power for avionics, flight instrumentation, lighting, and other electrically operated and controlled systems during normal operation. The electrical system also provides automatic switching from either battery or alternator to the essential bus in the event of an electrical system failure by the opposing alternator or battery. Two alternators and two batteries are used to ensure sufficient electrical power. Electrical power is supplied to the essential bus from both batteries and both alternators. Serials 0002 thru 1839, 1841 thru 1862, 1863 & subs w/o Air Conditioning: Alternator 1 (ALT 1) is a geardriven, internally rectified, 60-amp alternator mounted on the right front of the engine. Serials 1840, 1863 & subs w/ Air Conditioning: Alternator 1 (ALT 1) is a gear-driven, internally rectified, 100-amp alternator mounted on the right front of the engine. Alternator 2 (ALT 2) is a 20-amp engine-driven alternator mounted to the aft engine accessory pad. ALT 1 is regulated to 28 volts and ALT 2 is regulated to 28.75 volts. Both alternators are self-exciting (not selfstarting) and require battery voltage for field excitation in order to start up Battery 1 (BAT 1) is an aviation grade 12-cell, lead-acid, 24-volt, 10-amp-hour battery mounted on the right firewall. BAT 1 is charged from the Main Distribution Bus in the MCU. Battery 2 (BAT 2) is composed of two 12-volt, 7-amp-hour, sealed, lead-acid batteries connected in series to provide 24 volts. BAT 2 is charged from the circuit breaker panel Essential Bus. The bolster panel contains the pilot switches for operating ALT 1, ALT 2, BAT 1, and BAT 2. The switches are mounted adjoining so that a pilot can control all four switches with a single hand. Power generated from the alternators is fed into the Master Control Unit (MCU). The MCU regulates and distributes the power to the batteries and the system loads. Each alternator provides constant charging current for the corresponding battery and primary power to the aircraft electrical system during normal system operation. (See Figure 24-301)

EFFECTIVITY: All

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CIRRUS

AIRPLANE MAINTENANCE MANUAL

MODEL SR22

2. TROUBLESHOOTING Trouble

Probable Cause

Loose alternator wire connection. No alternator output. (Voltmeter Indicates 24 VDC or less and the ammeter indicates a Alternator switch off. discharge when the corresponding BAT switch is set to ON position) Defective alternator.

Alternator output is low.

No battery output.

High water usage (Battery 1).

Short battery life (Battery 1).

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Tighten connector. Turn on corresponding alternator switch. Replace alternator.

Circuit breaker activated (open).

Reset circuit breaker and troubleshoot circuit.

Faulty voltage regulator.

Replace voltage regulator.

Low engine RPM.

Increase engine RPM.

Loose alternator wire connection. Tighten corresponding connector. Faulty voltage regulator.

Replace voltage regulator.

Faulty MCU.

Replace MCU.

Faulty alternator.

Replace alternator.

Low engine RPM.

Increase engine RPM.

Poor battery connections.

Clean and tighten connections.

Faulty battery.

Replace corresponding battery.

Alternator output high, faulty volt- Replace MCU. age regulator. Faulty battery.

Battery will not hold charge.

Remedy

Replace battery.

Flights too short to recharge suffi- Remove corresponding battery ciently. and recharge when necessary. Loose connections, corrosion.

Tighten, clean, and neutralize connections.

Faulty battery.

Replace corresponding battery.

Standing too long (hot climate).

Remove corresponding battery and recharge when necessary.

Electrolyte level below top of plates.

Keep electrolyte level above plates.

Battery hold down loose.

Keep hold down secure at all times.

Overcharging of battery (faulty voltage regulator).

Replace MCU.

EFFECTIVITY: All

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AIRPLANE MAINTENANCE MANUAL

Trouble

Probable Cause

External power receptacle inoper- BAT 1 switch in OFF position. able. Faulty ground wire/connection.

Faulty ground power relay. Low volts light illuminates.

MODEL SR22

Remedy Set BAT 1 switch to ON position. Inspect and repair ground wire/ connection at receptacle or firewall ground bus bar. Replace MCU.

High demand on electrical system Increase engine RPM or load with a low engine RPM setting. shed. Faulty logic module or current sen- Replace MCU. sor.

Alternator is noisy.

No output from alternator 2.

Alternator 2 output is low.

Oil leaks from alternator 2.

EFFECTIVITY: All

Worn alternator bearings.

Replace corresponding alternator.

Faulty alternator diode(s).

Replace corresponding alternator.

Loose alternator wire connection. Tighten connector. Faulty alternator drive unit.

Replace alternator drive unit.

Faulty alternator.

Replace alternator.

Loose alternator wire connection. Tighten connector. Faulty rectifier.

Replace alternator.

Faulty MCU.

Replace MCU.

Low RPM.

Increase RPM.

Faulty oil seal in alternator.

Replace alternator.

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AIRPLANE MAINTENANCE MANUAL

Trouble Starter motor will not engage.

Probable Cause

MODEL SR22

Remedy

Starter relay circuit breaker open. Reset starter relay circuit breaker. If starter relay circuit breaker opens on second attempt, check for wiring short between circuit breaker panel and MCU. Loose electrical connections between MCU and starter motor.

Ensure all electrical connections to starter motor are secure.

Damaged electrical connections MCU 14600-001, 14600-002, between MCU and starter switch. 16600-001: At MCU, disconnect P108 and P109. Switch ignition switch to START. Verify resistance between pin E of P108 and pin B of P109 is zero. If infinite resistance is measured, check plugs, jacks, starter switch, and starter switch wiring for damage. MCU 19900-001: At MCU, disconnect P137 and P135. Set ignition switch to START. Verify resistance between pin C of P137 and pin C of P135 is zero. If infinite resistance is measured, check plugs, jacks, starter switch, and starter switch wiring for damage. Starter motor power relay faulty.

Remove positive cable from starter motor. Connect voltmeter to positive starter motor stud and ground. Set BAT 1 switch to ON position. Set ignition switch to START. Verify volt meter indicates 24 volts. If system voltage reads zero, MCU starter relay faulty. Return MCU to approved factory service center for service. If system voltage reads 24 volts, replace positive terminal on starter motor and attempt to start airplane. If starter motor still does not engage, replace starter motor. (Refer to 80-10)

Starter motor faulty.

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EFFECTIVITY: All

Replace starter motor. (Refer to 80-10)

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AIRPLANE MAINTENANCE MANUAL

Trouble

Probable Cause

MODEL SR22

Remedy

Starter motor engages when BAT MCU starter relay welded closed. MCU starter relay faulty. Return 1 master switch is set to ON posiMCU to approved factory service tion. center for service.

Annunciator Panel ALT 1 shows steady illumination above 2200 RPM.

Starter motor faulty.

Replace starter motor. (Refer to 80-10)

ALT 1 circuit breaker open.

Reset ALT 1 circuit breaker.

MCU 14600-001, 14600-002, 16600-001: MCU logic module faulty.

Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows normal currents and voltages and ALT 1 remains illuminated, replace MCU logic module. (Refer to 24-30)

MCU 14600-001, 14600-002, 16600-001: MCU current sensor faulty.

Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows ALT 1 current at zero or ± 60 amps, replace ALT 1 current sensor. (Refer to 24-30)

ALT 1 switch faulty.

Test ALT 1 switch: Verify continuity between pin 5 and pin 7 of J660 when switch is engaged.

At MCU, disconnect plug P111. MCU 14600-001, 14600-002, 16600-001: Short circuit between Verify ALT 1 turns off. annunciator panel and MCU. If ALT 1 remains illuminated, a short exists within the airplane wiring. Check plug P111 and jack J111. If no shorts are found, replace annunciator panel. (Refer to 3150)

EFFECTIVITY: All

MCU field control module faulty.

At alternator 1 with alternator cables attached, measure voltage between field input and ground. If voltage does not measure 20-24 volts, replace MCU field control module. (Refer to 24-30)

Alternator 1 faulty.

At alternator 1, measure resistance between field connector and ground. If resistance shows open circuit, alternator coil is damaged. Repair or replace alternator 1. (Refer to 24-30)

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AIRPLANE MAINTENANCE MANUAL

Trouble Annunciator Panel ALT 2 shows steady illumination above 2200 RPM.

Probable Cause

MODEL SR22

Remedy

ALT 2 circuit breaker open.

Reset ALT 2 circuit breaker.

MCU 14600-001, 14600-002, 16600-001: MCU logic module faulty.

Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows normal currents and voltages and ALT 2 remains illuminated, replace MCU logic module. (Refer to 24-30)

MCU 14600-001, 14600-002, 16600-001: ALT 2 current sensor faulty.

Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows ALT 2 current at zero or ± 60 amps, replace ALT 2 current sensor. (Refer to 24-30)

ALT 2 switch faulty.

Test ALT 2 switch: At jack J661 verify continuity between pin 5 and pin 7 when switch is engaged.

MCU 14600-001, 14600-002, At MCU, disconnect plug P111. 16600-001: Short circuit between Verify ALT 2 turns off. annunciator panel and MCU. If ALT 2 remains illuminated, a short exists within the airplane wiring. Check plug P111 and jack J111 for damage. If no shorts are found, replace annunciator panel. (Refer to 3150)

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ALT 2 field control module faulty.

At alternator 2, disconnect J125. Measure voltage between one pin on jack J125 and ground. If voltage does not measure 20-24 volts, replace ALT 2 field control module. (Refer to 24-30)

Alternator 2 faulty.

At alternator 2, disconnect jack J125. Measure resistance between one pin on jack J125 and ground. If resistance shows open circuit, alternator coil is damaged. Repair or replace alternator 2. (Refer to 24-30)

EFFECTIVITY: All

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AIRPLANE MAINTENANCE MANUAL

Trouble Annunciator Panel LOW VOLTS illuminated.

Probable Cause

MODEL SR22

Remedy

MCU 14600-001, 14600-002, 16600-001: Alternator switch faulty.

Set BAT 1 switch to OFF position. At MCU, disconnect plug P108. Connect pin D of jack J108 to ground. If LOW VOLTS illuminates, a short exists within the airplane wiring. Check plug P108 and jack J108 for damage. If no shorts are found, replace annunciator panel. (Refer to 3150)

MCU 14600-001, 14600-002, 16600-001: MCU logic module faulty.

Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows normal currents and voltages and LOW VOLTS remains illuminated, replace MCU logic module. (Refer to 24-30)

MCU field control module faulty.

At alternator 1 with alternator cables attached, measure voltage between field input and ground. If voltage does not measure 20-24 volts, replace ALT 1 field control module. (Refer to 24-30) At alternator 2, disconnect J125. Measure voltage between one pin on jack J125 and ground. If voltage does not measure 20-24 volts, replace ALT 2 field control module. (Refer to 24-30)

Annunciator Panel ALT 1 flashing. MCU 14600-001, 14600-002, 16600-001: MCU logic module faulty.

MCU 14600-001, 14600-002, 16600-001: MCU current sensor faulty.

EFFECTIVITY: All

Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows normal currents and voltages, set ALT 1 switch to OFF position. If ALT 1 continues flashing or turns off, replace MCU logic module. (Refer to 24-30) Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows ALT 1 current at zero or ± 60 amps, replace ALT 1 current sensor. (Refer to 24-30)

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AIRPLANE MAINTENANCE MANUAL

Trouble

Probable Cause

Annunciator Panel ALT 2 flashing. MCU 14600-001, 14600-002, 16600-001: MCU logic module faulty.

MCU 14600-001, 14600-002, 16600-001: MCU current sensor faulty.

Annunciator Panel ALT 1 does not ALT 1 circuit breaker open. illuminate when ammeter shows Loose electrical connections at no current. MCU.

MODEL SR22

Remedy Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows normal currents and voltages, set ALT 2 switch to OFF position. If ALT 2 continues flashing or turns off, replace MCU logic module. (Refer to 24-30) Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows ALT 2 current at zero or ± 60 amps, replace MCU current sensor. (Refer to 24-30) Reset ALT 1 circuit breaker. Ensure all electrical connections at MCU are secure.

MCU 14600-001, 14600-002, Set BAT 1 switch to ON position. 16600-001: Open circuit between At MCU, disconnect P111. MCU and annunciator panel. Connect pin F on plug P111 to ground. If ALT 1 does not illuminate, a short exists within the airplane wiring or annunciator panel is faulty. (Refer to 31-50) MCU 14600-001, 14600-002, 16600-001: MCU logic module faulty.

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EFFECTIVITY: All

Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows normal currents and voltages, replace MCU logic module. (Refer to 24-30)

CIRRUS

AIRPLANE MAINTENANCE MANUAL

Trouble Annunciator Panel or ALT 2 does not illuminate when ammeter shows no current.

Probable Cause

MODEL SR22

Remedy

ALT 2 circuit breaker open.

Reset ALT 2 circuit breaker.

Loose electrical connections at MCU.

Ensure all electrical connections at MCU are secure.

MCU 14600-001, 14600-002, Set BAT 1 switch to ON position. 16600-001: Open circuit between At MCU, disconnect plug P111. MCU and annunciator panel. Connect pin G on plug P111 to ground. If ALT 2 does not illuminate, a short exists within the airplane wiring or annunciator panel is faulty. (Refer to 31-50)

No power when BAT 1 master switch set to ON position.

MCU 14600-001, 14600-002, 16600-001: MCU logic module faulty.

Perform Operational Inspection Master Control Unit. If MCU Operational Inspection shows normal currents and voltages, replace MCU logic module. (Refer to 24-30)

BAT 1 master switch faulty.

MCU 14600-001, 14600-002, 16600-001: Disconnect negative cable from battery 1. At MCU, disconnect P108. Set BAT 1 switch to ON position. Measure resistance between pin D of jack J108 to ground. If resistance shows open circuit, test BAT 1 master switch and replace if necessary. (Refer to 31-10) MCU 19900-001: Disconnect negative cable from battery 1. At MCU, disconnect plug P137. Set BAT 1 switch to ON position. Measure resistance between pin K of J137 to ground. If resistance shows open circuit, test BAT 1 master switch and replace if necessary. (Refer to 31-10)

MCU 14600-001, 14600-002, 16600-001: BAT Current Sensor faulty.

EFFECTIVITY: All

Disconnect negative cable from battery 1. At MCU, disconnect plug P108. Set BAT 1 switch to ON position. Measure resistance between pin D of jack J108 to ground. If resistance shows open circuit, test BAT current sensor and replace if necessary. (Refer to 24-30)

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AIRPLANE MAINTENANCE MANUAL

Trouble No external power when BAT 1 master switch set to ON position.

Probable Cause BAT 1 master switch faulty.

MODEL SR22

Remedy MCU 14600-001, 14600-002, 16600-001: Disconnect negative cable from battery 1. At MCU, disconnect plug P108. Set BAT 1 switch to ON position. Measure resistance between pin D of jack J108 to ground. If resistance shows open circuit, test BAT 1 master switch and replace if necessary. (Refer to 31-10) MCU 19900-001: Disconnect negative cable from battery 1. At MCU, disconnect plug P137. Set BAT 1 switch to ON position. Measure resistance between pin K of J137 to ground. If resistance shows open circuit, test BAT 1 master switch and replace if necessary. (Refer to 31-10)

Ammeter pegs at ± 60 amps or indicates abnormal amperage.

MCU 14600-001, 14600-002, 16600-001: BAT current sensor faulty.

Disconnect negative cable from battery 1. At MCU, disconnect plug P108. Set BAT 1 switch to ON position. Measure resistance between pin D of jack J108 to ground. If resistance shows open circuit, test BAT current sensor and replace if necessary. (Refer to 24-30)

ALT 1 current sensor faulty.

Replace ALT 1 current sensor. (Refer to 24-30)

ALT 1 circuit breaker opens during ALT 1 field control module faulty. operation.

Replace ALT 1 field control module. (Refer to 24-30)

ALT 2 circuit breaker opens during ALT 2 field control module faulty. operation.

Replace ALT 2 field control module. (Refer to 24-30)

Airplane power remains on after BAT 1 master switch set to OFF position.

Test BAT 1 master switch and replace if necessary. (Refer to 3110)

BAT 1 master switch faulty.

MCU battery 1 power relay faulty. MCU battery 1 power relay faulty. Return MCU to approved factory service center for service. BAT 2 master switch set to ON position energizes non-essential equipment.

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P109 and P115 connectors switched.

Plug connectors correctly.

Power diode shorted.

Replace power diode.

Bad isolation diode on PFD, turn coordinator, or attitude indicator.

Replace diode.

EFFECTIVITY: All