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Maintenance TroubleShoot
Aircraft Alternator TroubleShoot |
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Check for open or ground-shorted alternator field. Most 12V alternators will have 3-6 ohm resistance, the 24V ones will be 10-18 ohm. Shorted alternator fields will destroy most voltage regulators. If the alternator has a field to ground short, do not connect the unit to it. |
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Prestolite alternators with two field terminals (F1 & F2). Measure field resistance between F1 and F2 |
With the engine off check voltage drops across the field and alternator circuit breakers and OV relay. High voltage drop means excessive junction resistance and will lead to many problems like:
fluctuation ammeter, charge meters and panel lights.
| With Master Switch off: | 12V values | 24V values |
| Field Resistance at ALT | 3-6 ohm | 10-18 ohm |
| Field Resistance at ACU | 3-6 ohm | 10-18 ohm |
| Field SW resistance | 0-0.1 ohm | 0-0.0 ohm |
| Field / circuit breaker resistance | 0-0.05 ohm | 0-0.05 ohm |
| Alt / circuit breaker resistance | 0-0.05 ohm | 0-0.05 ohm |
| With the field wire connected to the ACU & the Master switch on: | 12V values | 24V values |
| Buss voltage engine off | 12-13V | 24-26V |
| ACU/Reg input voltage | 12-13V | 24-26V |
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Alternator circuit breaker opens when master switch turned on - engine not running. Alternator out light inoperative Alternator induced radio noise Burned connector wire in regulator Checking alternator rectifier assembly Gear driven alternator inspection procedure High voltage warning light illuminates. Battery uses excessive water Low voltage warning light illuminates. Alternator will not fully charge battery. Over-voltage induced tripoffs of electrical system Voltage limiter contacts burned
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Shear drive used on Continental 520 engines. When this drive gets old it starts to slip and you get an intermittent alternator |
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