REFLECTOR: 12 Volt .vs. 24 Volt

[Douglas Holub]

I saved a lot of weight, improved reliability, and improved my c.g. by using 
a 24 volt electrical system.  Since the electrical current budget gets cut 
in half in a 24 volt system, the typical 40 amp belt driven alternator 
hanging near the prop of a Lycoming engine only needs to be 20 amps. I 
selected my radios and electrical accessories for low current consumption so 
that with everything on I'm drawing less that 9 amps at 28 volts. That 
includes comm, transponder, engine monitor, GPS, Dynon D10A, strobes, nav 
lights, landing light, and heated pitot. So I am able to power the airplane 
using only B&C's SD20 gear driven alternator that mounts on the vaccuum pump 
pad. No belt, less weight, and it moves the alternator closer to c.g.

The only drawback to using B&C's SD20 is that it doesn't charge when the 
engine is running below 1900 RPMs.  An alarm goes off in my engine monitor 
when the battery isn't being charged, so I use that to remind myself to 
extend my nose gear. When I pull the power back to land, my engine monitor 
alarm goes off, and that reminds me to drop my gear.

Doug Holub
built and flying N2980W

----- Original Message ----- 
From: "Brooke Wolf" <bwolf1 at tds.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Sunday, May 17, 2009 2:31 PM
Subject: REFLECTOR: 12 Volt .vs. 24 Volt


> All
>
> Almost every time I start a new phase in the building process of my 
> XLRG-5, I am a bit slowed because I have not decided on an electrical 
> system. I would be interested in hearing the opinions of the  collective 
> as to any advantage of a 24 volt system.  It would save  some weight with 
> smaller gauge wire, but I think the weight savings in  negligible.  Other 
> than that, I can't think of an advantage.  One  major sticking point in 
> the decision making process is Cessna, Cirrus,  and others.  Are they 
> putting 28 volt systems in their new airplanes?   If so, one would assume 
> there are good reasons for doing so.  Does any  one know what those good 
> reasons might be?  I've got to get off this  fence and get on with my 
> project!!
>
> BTW I plan on a robust electrical system (probably 2 alternators, 1 
> battery) to support a fairly sophisticated IFR panel with sufficient 
> redundancy for serious weather flying.
>
> Thanks.....Brooke _______________________________________________
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