REFLECTOR: 24 volt electrical system

[Dave Bertram]

I would like to make one comment about engine start.  I have a Blue Mtn.
EFIS and it is on during engine start.  I have had no problems with losing
any of my EFIS data.  This includes my engine indications.  I do have the
Chevy v-8 which may start easier.  

Dave Bertram
N350TX 
 
-------Original Message-------
 
From: Velocity Aircraft Owners and Builders list
Date: 09/27/06 12:06:53
To: Velocity Aircraft Owners and Builders list
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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