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hasbroucka(at)yahoo.com
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 Posted: Mon Jan 28, 2013 2:26 pm Post subject: Load Calculations and bus layout for comment |
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I am developing my first ever wiring plan for a 914 powered SeaRey amphibian kit. It is to be VFR night capable, and definitely will be Dynon SkyView system, two screens (planning only one to have backup battery). I intend to use ATC fuses for most circuits, and utilize Bob’s Z-16 drawing. I have attached my load calculations with the best info that I have. I do not know the constant load for the com? I also see a problem with cold night flight, because my load seems to exceed my alternator output with heater and lights running. These SeaRey planes typically have HID landing lights, plus taxi lights (I plan LED landing lights, no taxi lights). I intend to use only the internal alternator on my 914 Rotax, rated at 22a max, 20a at 5000rpm, and Auto pilot is preferred, but will be eliminated if it requires another alternator. This load came as a surprise because other than AP, many are equipped similar to this plan. I called Dynon hoping that the second screen will draw less, but they say it will draw 3 to 3.5a.
Plane has electric landing gear, electric trim, sump pump and a 2nd electric fuel pump for take-off, but being intermittent loads, I did not include them in my running load.
I would appreciate any input at all, and request help with refining or managing my load to fit the alternator, and also comments on my Buss layout.
My landing gear uses 4 small relays, do I understand correctly that even these small relays should have a diode across them for contact life and spike reduction?
I will start putting together my wire sizes, and intend to use a max 8% wattage loss to size wires for everything except the starter, and use wire size at 10deg rise to dictate fuse size according to AE Connection chart fig 8-3.
Can anyone tell me what to use as the max V-drop when sizing wires?
Thanks in advance,
Alan ,
HasbrouckA(at)yahoo.com
SeaRey Amphibian, framework and hull assembled (not covered). Working on VFR avionics and wiring (Dynon Skyview full suite). Top Priority is keep it light, and place weight forward!
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Tue Jan 29, 2013 7:25 am Post subject: Re: Load Calculations and bus layout for comment |
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A half amp can be saved by reducing the holding current of the master relay after starting. This subject has been discussed here in the past. Or the master can be shut off after starting and an automotive relay turned on in parallel (with engine starting disabled).
The "Charge LED" current seems excessive by a factor of 10. It is not needed anyway because the SkyView has built-in low voltage warning.
The O.V. relay coil current is too high. Relays are available with less than 0.1 amp coil current.
The landing light does not need to be counted as part of the continuous load. After landing, the battery should be put on a charger - maintainer.
The second SkyView can be turned off most of the time and used only when needed. Or consider a D-180 or other EFIS that uses less current. (And less weight, less cost)
I would definitely have an autopilot. To me, that is more important than a second EFIS.
The flight control indicators are all built into the SkyView. Separate indicators are not needed.
The Rotax voltage regulator / rectifier is the weak link in the charging system. It should be kept cool! And not operated at maximum.
Joe
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