REFLECTOR: 24 volt electrical system

[Chuck Jensen]

Andy,
 
Good arguments all, however, I'd suggest visiting the Aeroelectric List
at http://www.matronics.com/Navigator?AeroElectric-List
<http://www.matronics.com/Navigator?AeroElectric-List>  (go to
subscribe/unsubscrite and make the second selection for Aeroelectric
List), then do a search for the 24v v. 12v discussions.  Bob Nuckols,
the e-guru, has nothing against 24v, but offers countervailing arguments
that the bother and extra expense may well not be worth it.  I believe
his estimate of the actual weight savings with lighter wiring was more
in the 2-3 pounds range.  Anyhow, its an interesting forum and very much
addresses this and other e-issues.  As usual, there is no right or wrong
approach, just different trade-offs.

Chuck Jensen 
Do Not Archive  

	-----Original Message-----
	From: reflector-bounces at tvbf.org
[mailto:reflector-bounces at tvbf.org] On Behalf Of Andrew Ellzey
	Sent: Wednesday, September 27, 2006 12:52 PM
	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 <mailto:romott at adelphia.net>  
		To: Velocity Aircraft Owners and Builders list
<mailto:reflector at tvbf.org>  
		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=&FamID=715&DivID=
&GID=&Type=2&ID=364&TechID=&PSID=3773 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 <mailto:ajlz72756 at yahoo.com>

			To: Velocity Aircraft Owners and Builders list
<mailto:reflector at tvbf.org>  
			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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