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2 Answers

PA-44 Electrical System

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Aircraft Systems

Hi- I am learning about the electrical system in the Seminole, but am having a hard time understanding the complexities of the schematic in the POH. I cannot find anything helpful on the internet beyond a token rote overview! I know what the voltage and amperage is, and I know the extreme basics. Can someone provide me with an abbreviated description, maybe a short paragraph or so (one that a Commercial DPE would be happy with) or perhaps even better, a simplified schematic? Thank You!

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2 Answers

  1. Brian on Nov 03, 2013

    Read about the system out of the POH, any information there can be asked. As for the electrical diagram, at least know the buses; if memory serves there are 5. If you can draw it, great, but I doubt you’ll find a DPE that will ask you to. Your school on the other hand, well it depends on their attitude towards it.

    A DPE might ask you how you know the current load on your system and how it relates to battery amperage. Or when overload lights illuminate. The procedure to recycle the system. What instances might result in need to cycle the alternator. All of this and more is found in the POH in section 7.

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  2. Bruce J. Sato CFI, CFII on Nov 19, 2013

    The way I would say it would be:

    The seminole is equipped with a 14 volt electrical system
    Which utilizes push-pull type circuit breakers
    12 volt 35 amp hour battery
    Two 70 amp engine driven alternators.

    Don’t say the following unless he asks you!!!

    Voltage regulators help maintain a constant 14 volt output from each alternator which effectively shares the electrical load.

    Loss of 1 alternator is indicated by an annunciator light and a zero indication on the loadmeter. Remaining alternator will normally provide adequate electrical power.

    Over voltage protection is provided if the system voltage exceeds 17 volts. Should an over voltage occur the battery is then the whole source of electrical power.

    The battery is used as a source of emergency electrical power and for engine starts.
    High drain items include:
    Vent fan
    Gear hydraulic pump

    Hope this helps and good luck!

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