REFLECTOR: 24 volts vs. 12 volts

[KeithHallsten]

Actually, many circuits in the plane will be minimum practical wire size.  Personally, I don't use anything smaller than 22 Ga - it's too fragile and hard to terminate.  (The one exception might be wires to switches on the stick grip, where flexibility and space savings are key considerations.  Then special methods have to be used to install connectors.) From a purely electrical standpoint, some circuits could use a smaller wire, but it's just not practical.  

The only wires in our planes that are big enough and long enough for weight to be non-trivial are the 2 GA wires between the battery and the starter.  It's possible that a 28-volt battery and starter could let you drop those to 4 GA, but that's going to be the only significant weight savings to be had.

A bigger consideration is availability and price of avionics and other electrical components.  You will generally find that the lower-cost alternative is to go with 14-volt components, since they are mass-produced for cars and boats and such.  

However, the voltage drop during engine start is often less of an issue with 28-volt electronic components.  Since the power supplies in many avionics will operate over a fairly wide range, it's often the same hardware sold for either bus voltage.  However, during engine start a 14-volt system may drop to 7 or 8 volts, which may cause your engine monitor or GPS to quit and re-start.  When a 28-volt bus gets pulled down to 14 to 16 volts by the starter, everything will generally keep working.  The cheap and easy solution to this with a 14-volt bus is usually a small back-up battery to keep the avionics up during engine start.

All things considered, I'm putting in a 14-volt system.

Keith Hallsten, XLFG
      
  ----- Original Message ----- 
  From: Douglas Holub 
  To: reflector at tvbf.org 
  Sent: Sunday, January 16, 2005 7:37 PM
  Subject: REFLECTOR: 24 volts vs. 12 volts


  If I have a 24 volt system I'll use half the current so my wires can be smaller by 1/2 and I'll save a pound or two. What's the downside?

  Doug


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