REFLECTOR: 24 volt electrical system

[Scott Baker]

Andy,
Everything you say has merit.
I think, however, that the advantages of building an Experimental aircraft with a 12-volt system "trumps" all the good points that you mention.
12-volt automotive alternator ... $200 something
12-volt accessory plugs for cell phones, computers
12-volt interior lights and other "do-dads" borrowed from the marine and RV world ...12v bilge fans and hair dryers for forced air cabin heat and defrost, map lights, great DVD/CD players, and the list goes on.
12-volt means $$ saved on equipment.  24-v 12volt battery at Sears ($) versus a 24-volt Gill ($$$).
Best regards,
Scott B.
  ----- Original Message ----- 
  From: Andrew Ellzey 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Wednesday, September 27, 2006 12:51 PM
  Subject: Re: REFLECTOR: 24 volt electrical system


  I have a solution to change everything to 24 volt except the high amperage draw for the gear pump. Here are some of the reasons to go to 24 volt. This is from a booklet (Aircraft wiring for smart people) on the Blue Mountain web site written by Greg Richter at BM. BM also has a power board that has power regulation and control for all the 12 volt trim motors. I am considering using their power board on my install. This doesn't mandate that I have to go to 24 volt, just adds the option.

  As of mid-2004, just about everything you can buy in avionics will run on 10-32 volts DC and doesn't care either way. single voltage items like landing lights and strobes can be all be had at 24 volt versions now so this isn't a problem either.

  Since a given load draws half the current at 24 volts that it does at 12 you can use smaller wire with the same results. you can use wire that's only 1/4 the size, which is a pretty big deal when you're are running #18 and everyone else is running #14. Most small planes have nearly 50 pounds of wire in them. How would you like to save 10 pounds of dead weight?

  Engine start will drop a 12-volt system to around 9 volts causing EFIS systems to reboot, radios to loose presets and fuel totalizers to restart. A 24 volt system will only drop to about 18 volts during engine start, which is well above the 10.5 volt minimum for modern, digital avionics. No backup batteries, no switching, no relays, and no fiddly, complex systems to solve a non-problem.

  A 24 volt system also has a lot more reserve energy available for use than a 12 volt system. As a point #2, a failed alternator in a 12 volt system leaves you a 2 volts from shutdown. A 24 bolt system you've got a lot more reserve before your avionics and FADEC (If you have the money for FADAC) drop offline. Look at discharge curves, and you'll see that a 12 volt battery at 11 volts is only partially discharged. A 24 volt battery at 11 volts is very close to dead.

  There are a lot more reasons these are just a few.

  Andy


    ----- Original Message ----- 
    From: Ron Brown 
    To: Velocity Aircraft Owners and Builders list 
    Sent: Wednesday, September 27, 2006 10:31 AM
    Subject: Re: REFLECTOR: 24 volt electrical system


    Andrew,

    Is there a particular reason you want to use 24 volts?  Since you are building your own airplane, you have lots more choices for equipping the airplane and lots more stuff is available for 12 volt systems from the automotive and marine worlds.  

    If you have to have 24 volts because of good deals on avionics, then you could go to http://www.parker.com/frameless/default.asp?substDivId=&FamIDq5&DivID=&GID=&Type=2&ID64&TechID=&PSID773 and order a replacement 24 vdc motor for your hydraulic pump.

    I understand the elevator trim system is already 24 volt (slows down the trim action since the motor runs slower on 12 volts).  You could probably use a power resistor in series to slow the trim motor down.

    Ronnie
      ----- Original Message ----- 
      From: Andrew Ellzey 
      To: Velocity Aircraft Owners and Builders list 
      Sent: Wednesday, September 27, 2006 10:27 AM
      Subject: REFLECTOR: 24 volt electrical system


      I would have liked to use a 24 volt electrical system on my aircraft, the problem is the hydraulic gear pump system being 12 volt @ 30 amp. Has anyone flying an XLRG found a way around this issue?

      Andy Ellzey


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