gordonrsmith921@yahoo.com
Joined: 06 Oct 2009
Posts: 24
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 Posted: Tue Aug 10, 2010 7:36 am Post subject: Was-Power Schematic for Review-now-Mission Statement & Load |
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I would like to answer Bob N.’s points and questions from July 30, 2010, in parts. This is about the Mission Statement and Load Analysis for a Jabiru 3300 powered Sonex.
Mission Statement: - Principally to be a Day VFR Recreational Aircraft.
- Capability of Occasional Day VFR Cross Country.
- Capability of Occasional Night VFR.
- Capability of limited IFR (no intentional hard IFC) if accidentally caught ON-TOP and needing a clearance to descend through a layer. I remember that the first C-150 that I trained in had this capability. I was trained under the hood for recovery from unusual attitudes (in case of accidentally doing something stupid).
EFIS backup would include a slip/skid indicator and a panel mounted second GPS with a couple of hours of internal battery power. This could provide approximate airspeed and GPS generated attitude information. I understand that this is limited info, however in a stable decent can be used with understanding of its limits. I am planning no ground based NAV receiver capability.
I understand that this aircraft has limited alternator capacity (20A.) and panel space. I am planning that the main AC battery will be an Odyssey PC625 at 17 or 18 AH capacity. I find that in modern avionics and lighting, there are some very efficient (if expensive) options. Lighting for this AC will be all LED or HID, inside and out. I intend wing tip LED Strobe/Position lights and Wig-Wag HID landing lights for day or night visibility of the AC. There are electrically efficient avionics that include remote COMs (with internal intercom), remote Transponder all commanded by the EFIS (minimum panel space required).
I have completed an Excel spreadsheet Load Analysis. This can be posted if anyone wants to see the detail. The highest E-bus load under all conditions day or night is under 5 Amps. The highest Main Bus load, day is less than 9 Amps – night is just over 11 Amps. Total max loads runs under 14 Amps Day (using Wig-Wag & Strobes); night max is a little over 16 Amps on decent to landing (less than 15 Amps in night cruise). This appears to meet the recommended 75% max load condition total bus loads.
If I am underestimating E-bus load and it will be as much as 6 or 7 Amps, this should be OK with a simple Switch for E-bus alternate feed and no need of a relay. At 5 or 6 Amps E-bus load, is a heat sink needed for the normal feed diode mounted on aircraft structural metal? Also with this E-bus load perhaps the E-bus feeds should be downsized from 16AWG to 18AWG or even 20AWG?
Also Bob wrote:
The devices on your
e-bus may not need brownout protection if the internal
resistance of the main battery combined with inrush
characteristics of the starter don't depress the
bus enough to cause re-sets.
Does anyone have any data or experience regarding this point? Given starting a Jab3300 with a PC625 battery in good condition during ambient conditions of greater than 60 degrees F.?
Gordon Smith
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