REFLECTOR: Bus, Battery & Back Order

[Al Gietzen]

Subject: RE: REFLECTOR: Bus, Battery & Back Order

 

Al,

Thanks for the panel pic.  Can I ask you if you have a hot batt bus as well 

as an essential bus and a main bus?  Could you tell me your decisions on 

what went to hot and ess bus'es?  In the event of alternator failure will 

you be doing manual depowering (at the unit) anywhere?  I get the theory 

fine.  Seems for me the devil is in the details.

 

Yes; I have a "hot" bus (what I like to call the "Critical" bus).  It is
connected to both batteries, but isolated with 60A Schottky diodes so if one
or the other batteries goes down (bad short somewhere), the other still
provides power.  The "Critical" bus drives fuel injection (two separate
sets, primary and secondary), Electronic ignitions (two separate sets,
leading and trailing) fuel pump 2, backup ECU, and backup EFIS (PFD and
AHRS).

 

The "Essentials" bus drives: ECU, fuel pump 1, EFIS PFD & AHRS, Alt field,
SL-30 NAV/COM, Transponder, Engine monitor, Landing gear, Pitot heat, and
landing light.

 

The "Distribution" is connected via a 30A breaker/switch, and it drives
position lights/strobes, vent and heater blowers, moving map display,
interior lights, stereo/CD player, Auto pilot, Com 2, and misc, sensors
(fuel level, low level indicators for coolant, oil, etc.)

 

The Ess and Dist buses are downstream from the battery contactors powered by
both batteries.  I will normally have Batt 2 as a backup and the contactor
off except for cold start, or alt failiure.  Batt 2 is charged via a
Schottky diode when it is off.  I have two Odyssey batteries and plan to
change one out every 2 years.

 

Different folks I'm sure would make some different choices.  The idea here
is that loss of alternator, or some mysterious heavy draw, one would first
hit the distribution bus switch to shutoff nonessential loads; then consider
what items of the Ess bus can or need to go.  In the event of serious
shortout of the main power distribution, I can turn off both battery
contactors and the fan keeps turning.  This situation would most likely
require a windmilling prop for restart. 

 

Where ever I went after redundany, I tried to keep the wiring separated.
The critical bus is in front of the canard bulkhead, the other two behind
the panel.  The main ground path is a copper pipe through the L side duct,
with ground buses before and aft the firewall, behind the panel and up front
near the batteries.  Most of the power leads run inside the pipe.

 

If you have time, I'd be happy to hear you explain that panel layout.  Looks


real nice.

 

Thanks.  I'll try to get something about panel layout on my website, and
then refer you there.

 

Best,

 

Al

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20050617/a8a1d180/attachment-0001.html