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External 12V Power Question

Tcheairs

Well Known Member
Lots of posts on the addition of 12v external power source. Most say bypass the battery and master switch. But I am unclear as to why the bypass. If the input power from the external (battery or a switchable 30a power supply) is equal to or greater than the voltage on the airplane's battery and the correct gauge wire used, what is the concern?

I'd like to fire up my Dynons and do some hangar flying since I'm new to these avionics. I'm running an Odyssey 12v primary and backup battery on my RV7A..

Thanks
 
I’ll try...

I am not a specialist in electronics, but i had the same question once so i might be of any help.
People who know better than me, please step in any time....

If you have a glass cockpit a external power supply is good to have for numerous and obvious reasons (training, familiarization, programming, etcc).

If you just want to charge your battery when it is dead or want to play around with your EFIS it is okay to hook the external power directly on the battery poles.
Then you have complete control about your panel via the master switch.



If you want to charge your battery when it is dead, want to play around with your EFIS
AND WANT TO BE ABLE TO JUMPSTART YOUR AIRCRAFT THROUGH THE EXTERNAL POWER SUPPLY
hook it up to the main Bus. In this case, when jumpwired and master switch off, the battery is not drawing any power to re-charge itself and everything is going to the starter. The battery is not buffering/damping any current or voltage.
Once the engine is running, flip on the master and charge the battery with your alternator.
If you want to charge your battery on ground just connect the external and switch on the master.

That is at least the science behind my decision on my electrical system.
 
I hook up my 12v source directly to the battery to work on avionics. Just turn on the master and everything works fine.
Just make sure you are putting in enough amps to run everything you are using or it will discharge the battery.
For me, this method has worked for many years with no issues.
 
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