Power Distribution and Buses
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I am continuing to fumble my way through designing my electrical system, but I'm curious how you guys are designing your buses and handling power distribution.
I'm only barely not totally electronically illiterate so I've been figuring this out pretty gradually, but after reading the AeroElectric Connection book and listening to some podcasts and youtube videos, I think I have a decent start.
I have also significantly plagiarized the following examples so far:
Bob Nuckolls figure Z-11 (pretty much this: https://bandc.com/wp-content/uploads/20 ... le_alt.pdf)
Noel Wade's Diagram: http://sonexbuilders.net/viewtopic.php? ... ric#p26716
Frank Alvarez's Diagram: http://sonexbuilders.net/viewtopic.php?f=6&t=1564
Background:
-I'm using an Aerovee Turbo, so 20A alternator, with coils & mags for ignition
-I'm going to build a Garmin G3X Touch system. So one display, engine interface box, ADAHRS box, magnetometer box, radio box, transponder box, and a GPS position source box is pretty much the avionics system.
Here's a list of all the electrical components I'm planning and their associated loads:
Anyway here are the questions I'm pondering right now:
1. I want to protect my avionics during engine start but still be able to monitor the engine while I start it. That means I will have to have at least the display and engine interface box powered up during the start. If I understand correctly, the Bob Nuckolls alternator control relay setup will allow me to keep the alternator offline until I switch it on, so there'd be no danger of alternator induced voltage spikes during startup. So the only remaining hazards would be voltage dips. Garmin recommends using a TCW power stabilizer to catch any dips during engine start (https://www.tcwtech.com/IPS-12v.htm).
The cheapest model supplies up to 4 amps, so if I went with one of those I could power the display (1.25A), engine interface (0.43A), GPS (0.2A), and radio (0.6A) for a total of only about 2.5 amps during start, and that should do it. Does that all sound right or is there something else I'm missing?
OK next:
2. Not really a specific question, just looking for some thoughts on buses. Seems like the basic and typical way to do it is to have a "main" bus powered whenever the battery contactor is on, then an "avionics" bus for the instruments. Then there are many Bob Nuckolls examples that forego the avionics bus but add an "endurance bus" for essential things in case of alternator failure. Would it not make more sense to just have the essential things on the primary bus, and all the less-than-essential stuff on a downstream bus? That way if you need to shed some loads you just switch that bus off and you're down to your essentials. Something like the attached picture is what I'm thinking.
Does that make any sense? Am I missing anything obvious, or any ways to make it more simple?
I'm only barely not totally electronically illiterate so I've been figuring this out pretty gradually, but after reading the AeroElectric Connection book and listening to some podcasts and youtube videos, I think I have a decent start.
I have also significantly plagiarized the following examples so far:
Bob Nuckolls figure Z-11 (pretty much this: https://bandc.com/wp-content/uploads/20 ... le_alt.pdf)
Noel Wade's Diagram: http://sonexbuilders.net/viewtopic.php? ... ric#p26716
Frank Alvarez's Diagram: http://sonexbuilders.net/viewtopic.php?f=6&t=1564
Background:
-I'm using an Aerovee Turbo, so 20A alternator, with coils & mags for ignition
-I'm going to build a Garmin G3X Touch system. So one display, engine interface box, ADAHRS box, magnetometer box, radio box, transponder box, and a GPS position source box is pretty much the avionics system.
Here's a list of all the electrical components I'm planning and their associated loads:
- Master Contactor - 1A
3ohm Coils x2 - 9.4A (or maybe 5ohm coils - 5.6A)
GDU 450 display - 1.25A
GEA 24 engine interface - 0.43A
Sonex fuel probe transducer - 0.1A
GSU 25C ADAHRS - 0.2A
GMU 11 magnetometer - 0.1A
GTR 20 radio - 0.6A (3A when transmitting)
GTX 45R transponder - 0.72A (1.3A max)
GPS 20A position source - 0.2A
ACK E-04 ELT - 0.16A (I think)
Aveo strobe lights - 2A peak
Aveo nav/pos lights - 0.51A
Duckworks landing lights x2 - 1.3A total
GSA 28 A/P servos x2 - 0.72A total (max 3.6A total)
iPad dock charger - 0.75A
12v Power outlet - ?
Interior LED lights - ?
Seat heat - ?
Sonex flap motor - ?
Turbo Cooler Fan & Water Pump - ?
Anyway here are the questions I'm pondering right now:
1. I want to protect my avionics during engine start but still be able to monitor the engine while I start it. That means I will have to have at least the display and engine interface box powered up during the start. If I understand correctly, the Bob Nuckolls alternator control relay setup will allow me to keep the alternator offline until I switch it on, so there'd be no danger of alternator induced voltage spikes during startup. So the only remaining hazards would be voltage dips. Garmin recommends using a TCW power stabilizer to catch any dips during engine start (https://www.tcwtech.com/IPS-12v.htm).
The cheapest model supplies up to 4 amps, so if I went with one of those I could power the display (1.25A), engine interface (0.43A), GPS (0.2A), and radio (0.6A) for a total of only about 2.5 amps during start, and that should do it. Does that all sound right or is there something else I'm missing?
OK next:
2. Not really a specific question, just looking for some thoughts on buses. Seems like the basic and typical way to do it is to have a "main" bus powered whenever the battery contactor is on, then an "avionics" bus for the instruments. Then there are many Bob Nuckolls examples that forego the avionics bus but add an "endurance bus" for essential things in case of alternator failure. Would it not make more sense to just have the essential things on the primary bus, and all the less-than-essential stuff on a downstream bus? That way if you need to shed some loads you just switch that bus off and you're down to your essentials. Something like the attached picture is what I'm thinking.
Does that make any sense? Am I missing anything obvious, or any ways to make it more simple?