How does the electrical system in a light aircraft such as a Zenith CH-750 or Cessna 150 work compared with electrical systems in larger aircraft? Are the system is different than the electrical system on a common car? Do we need static electric discharge system?

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    $\begingroup$ This feels too broad to me. Asking about some aspect of the electrical system of a typical airplane of some type (say, "how is interference from static discharges prevented in a Cessna 150/152?") is almost certainly fine. Asking basically for a full description of the electrical system of "small, slow, light" aircraft (whatever exactly that means; in fairness, you do offer two specific examples which helps narrow that part down) is something that could probably require one or more books to answer properly; that makes it too broad. $\endgroup$ – a CVn Dec 22 '18 at 16:08
  • $\begingroup$ "static electric discharge system" are just static wicks, having nothing to do with the electrical system except that they happen to be mounted on the same airplane. Here's an example of one aircraftspruce.com/catalog/elpages/… $\endgroup$ – CrossRoads Dec 22 '18 at 19:13

Typically light normal category aircraft make use of either a 14 VDC or 28 VDC electrical systems powered primarily by an engine driven alternator. This provides power to one or more power bus bars which provide electrical power to the various aircraft systems requiring it. Below is an example light aircraft electrical system from a Cessna 172S.

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One notable deviation from automobile electrical systems is that the engine spark plugs receive electricity from a separate pair of magnetos which produce their power independent of the main electrical system for reasons of redundancy.

  • $\begingroup$ And dual spark plugs per cylinder. $\endgroup$ – CrossRoads Dec 22 '18 at 19:17
  • $\begingroup$ Seems that there is two type voltage level in a small airplane, 12V and the 14volt. I do have to check that 14V as it it absolutely new for me. Or it just 12V plus 20% of it? Which it will give 14,4V that also common for heavy truck electrical system. $\endgroup$ – AirCraft Lover Dec 22 '18 at 23:03
  • $\begingroup$ From the second drawing, I saw there written 12V. That's the only voltage indicator there. Seems the voltage is 12VDC. 12V is not 12V if we measure using voltmeter. It must be at range 12V+(12V*15% - 12V*20%) or 13.8V - 14.4V. Lower than that, is too low. Higher than that range can endanger the devive, especially a sensitive one. $\endgroup$ – AirCraft Lover Dec 22 '18 at 23:11

Most light aircraft use 12vdc systems with belt driven alternators, like cars. They generally use the same alternators and voltage regulators, sometimes identical to the auto version but just having a more stringent quality control process.

Some heavier light planes use 24vdc systems, which allows for smaller, lighter wiring, and a bit less sensitive to bad connections with the higher voltage. More expensive to fix because the generators are dedicated aircraft units with no automotive equivalent.

For a homebuilt, you would just build a 12vdc system using automotive components, except for the battery, which has be be able to run upside down so it needs to be an aircraft one, although you could use an automotive gel cell battery.

  • $\begingroup$ Re "...but just having a more stringent quality control process": Or sometimes just having a higher price tag :-( $\endgroup$ – jamesqf Dec 22 '18 at 19:11
  • $\begingroup$ Well yes. The story I was told long ago was that a Delco alternator on the "aircraft" production line simply went through inspections or functional tests on every unit instead of every 10th. In the avionics industry, black boxes no longer use "milspec" electronic components like chips because they aren't manufactured any more. It's now a "Mil Perf" (performance) standard that applies and manufacturers screen commercial hardware through a Mil Perf testing regimen and the ones that pass are considered fit for flight. $\endgroup$ – John K Dec 22 '18 at 19:22
  • $\begingroup$ @johnk, what did you mean that the battery has to be able to run upside-down? What for? Even for non-acrobatic airplane? $\endgroup$ – AirCraft Lover Dec 22 '18 at 22:57
  • $\begingroup$ Wet cell batteries have to be vented. A normal airplane can experience 0 or negative G just from turbulence if it's bad enough, so aircraft batteries with vented cells have a check valve built into the cell caps. $\endgroup$ – John K Dec 23 '18 at 1:28
  • $\begingroup$ @John K: And you think cars, or at least pickups driven on some of the dirt roads hereabouts, don't experience negative G? $\endgroup$ – jamesqf Dec 23 '18 at 21:02

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