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To: lml@lancaironline.net
Date: Fri, 21 Dec 2007 15:46:26 -0500
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From: "Bill Wade" <super_chipmunk@roadrunner.com>
References: <list-2607650@logan.com>
In-Reply-To: <list-2607650@logan.com>
Subject: Re: [LML] Glass Panel Backup
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  I view a second battery as a way to maintain radio and transponder contact 
with ATC for as long as possible.

  I start up using both batteries and when the charge rate reaches a steady 
minimum I take one off line. I used MOV's on the contactors to absorb spikes 
as they're switched off since the avionics are kept on throughout.

  If anything happens to the alternator or the other battery I know I have a 
conservative (and easy to figure) 30 Amp-hours before voltage drops to 10V. 
The volt/amp shunt is wired to show battery charge/discharge rather than 
alternator load. If the alternator dies it then shows battery drain, making 
load shedding and time remaining calculations easier.

 (This is a 14V system using RG-35AXC Concordes.) At 10V I would've lost 
autopilot, HSI, 530, audio panel, and Xponder. Until then I'd still have a 
GX-60 and an SL-30 for navigation and communication, turn coordinator, 
vaccuum A/I, altimeter and all engine gauges. I'd be able to use the compass 
rose on the 496 to substitute for a DG.

  There's no question a second battery is a heavier way to go. Part of the 
gain was offset by removing lead ballast. That wouldn't apply with a new 
airplane. For the rest, my wife says I need to lose weight....      -Bill 
Wade