REFLECTOR: [c-a] Re: COZY: 24 Volts VS 12 Volts

[John Tvedte]

>From a practical standpoint 22awg is the smallest wire size one is likely to use in an GA aircraft.  Most of the wiring is going to be 20 or 22awg and shielded versions thereof...none of which is going to change if 12 vs 24V.  Pitot/Electric fuel pump/Alternator(s), feed wires and the starter are the 'fat wires'.  Even the alternator "B" field can be 20awg.


Here is one way to save weight for the starter and can double as main alternator feed.

http://www.periheliondesign.com/fatwires.htm

Suggest you use a field wound starter for best performance/lowest current draw.



-------- Original message --------
From: Clayton Chase <chasec at gmail.com>
Date: 10/07/2013 1:18 PM (GMT-06:00)
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Subject: Re: REFLECTOR: [c-a] Re: COZY: 24 Volts VS 12 Volts


I'd prefer to go with 24V but have chosen to use a 12V system because of the depth of pocket required to go up to 24V.  The equipment isn't any more expensive to make, however since there is not a demand for it like there is for the 12V equipment.  Due to the auto industry, almost everything you could want in a 12V part is mass manufactured.  Therefore I'll be using 12V in my plane even though it will add some weight in wires.


On Mon, Oct 7, 2013 at 9:37 AM, Dave Philipsen <velocity at davebiz.com<mailto:velocity at davebiz.com>> wrote:
Heh, heh...nice techno-humor!  The only point I'm trying to make with all of this is that, yes, there are some benefits with a 24v system.  There would be even more benefits with a 48v system and even a 96v system. But at some point the advantages of increasing the voltage diminish to a point where they are not really practical.  Obviously, for automobiles, the engineers decided almost universally that that point was at 12 volts. I believe that for our experimental aircraft the point is also at 12 volts. But, others with perhaps deeper pockets and a desire for slightly greater reliability and dependability may arrive at the point of 24 volts.


Dave Philipsen
Velocity STD FG
N83DP

On Oct 7, 2013, at 11:08 AM, Don Johnston <numa at comcast.net<mailto:numa at comcast.net>> wrote:

You are forgiven.

Now go say 50 "Hail Tesla's" and sin no more. :-)


On Mon, Oct 7, 2013 at 10:35 AM, Dave Philipsen <velocity at davebiz.com<mailto:velocity at davebiz.com>> wrote:
I messed up on the 24v calculations. Strike out the paragraph below and change to:

The same scenario with a 24volt 100 amp starter would work out to a 290 milliohm total resistance (starter is 240 milliohms and solenoid contacts are 50 milliohms). The circuit will now draw 82 amps and you will see 19.86 volts across the starter and 4.13 volts across the solenoid contacts.  This is a better scenario than the 12v system but not as exaggerated as the scenario you stated below.


Dave Philipsen
Velocity STD FG
N83DP

On 10/7/2013 10:15 AM, Dave Philipsen wrote:
The same scenario with a 24volt 100 amp starter would work out to a 170 milliohm total resistance (starter is 120 milliohms and solenoid contacts are 50 milliohms). The circuit will now draw 141 amps and you will see 16.9 volts across the starter and 7.1 volts across the solenoid contacts.  This is a better scenario than the 12v system but not as exaggerated as the scenario you stated below.

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