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  #11  
Old 10-01-2022, 09:18 PM
Walt's Avatar
Walt Walt is offline
 
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Location: Dallas/Ft Worth, TX
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Another good reason for an avionics master is to reduce battery load during start. Why have an additional 10 amp load sucking valuable energy from the battery when you crank the starter. Do you start with lights, strobes, pitot heat on?

How about smoke emanating from your 430 [this just happened the other day to a friend]. If you turn off the master things just got exciting.

Milspec switches/relays are extremely reliable.
Everything is a trade off, pick your poison.

Personally I’m a control freak, I like the ability to turn things on/off.
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EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
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  #12  
Old 10-01-2022, 09:53 PM
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Walt Walt is offline
 
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An example From the Cirrus SR22 flight manual, certainly one of the most modern GA aircraft around.

Avionics Power Switch
A rocker switch, labeled AVIONICS, controls electrical power from the circuit breaker panel bus to the Avionics Bus. The switch is located next to the ALT and BAT Master switches. Typically, the switch is used to energize or de-energize all avionics on the Avionics Non-Essential and Essential Buses simultaneously. With the switch in the OFF position, no electrical power will be applied to the avionics equipment, regardless of the position of the master switch or the individual equipment switches. For normal operations, the AVIONICS switch should be placed in the OFF position prior to activating the MASTER switches, starting the engine, or applying an external power source.
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Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 2000+ hrs, New Titan IO-370, Bendix Mags, MTV-9 prop
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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  #13  
Old 10-02-2022, 08:10 AM
Freemasm Freemasm is offline
 
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Location: Orlando
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Cirrus makes a nice aircraft but I wouldn’t copy everything they do. Their electrical systems utilize master control units, field control units, etc. (hopefully I got the names right). Per the COPAs I know, these make for nice operation when they behave; however, they tend to be problematic and expensive. Maintenance shops like to LRU them versus troubleshoot them to add to the pain.

Guessing the OP will keep any related actions simple.
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  #14  
Old 10-02-2022, 09:00 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
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Quote:
Why have an additional 10 amp load sucking valuable energy from the battery when you crank the starter. Do you start with lights, strobes, pitot heat on?
Every plane is different. Yes, I start with everything on. But my Rotax 912ULS starts so quickly that it doesn't matter. As soon as I turn the start key, the engine is running. An observer might notice a quarter turn of the propeller before it is turning too fast to see.
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  #15  
Old 10-03-2022, 08:33 AM
Southern Pete Southern Pete is offline
 
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Location: England
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Avionics master switches are single point failures that take down all of services powered from the switch if (when) it fails. If nothing else install an alternate supply path.
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