Actually, Tom,  in that particular incident - a second battery would have only enabled me to fly too far away from the only safe airport to make a return and dead stick into.  IF I had realized the root cause (a switch accidently put in the wrong position) then one battery would have worked just as well as two {:>). 

Having said that, I certainly would not try to get anyone to change their mind about using two batteries. . Some folks would not feel comfortable even with two batteries - but, would add a second alternator, etc.  So, you have to think through your scenarios, the risk involved and your personal risk tolerance.  Yes, Bob now has several good electrical designs - for just about any kind of power system you could come up with.  Back in 1992, I had never heard of Aeroelectric or Bob.

But, since my previous engine out almost 5 years previous had been fuel related and the engine was sputtering in a similar manner - my diagnostic side of the brain got locked in to searching  for a fuel problem (again) - but even switching tanks did no good - because, this time the "fuel problem" was a decreasing electrical power.  This incident clearly pointed out the need for an emergency check list that involved checking both fuel AND electrical systems.  Coming up with one in your head with the engine sputtering is not recommended {:>)

Contributing factors were two early design decisions that on hindsight revealed shortcomings.  

One was an electrical system design that permitted my voltmeter to keep showing me the 13.8 volts being generated by the alternator while the battery voltage was steadly decreasing.  Yes, I had a low-voltage light right in front of my eyes - but, it was wired into the alternator powered circuit - so never showed low voltage because the alternator voltage was fine - up to the point the relay released.

   Now,  had  it occurred to me I might have an electrical problem - and switched the volt meter to the battery (instead of alternator) AND had thought to observe it, I would have seen the battery voltage decreasing and that MIGHT have got me looking for an electrical problem rather than a fuel problem.  But, when you get your head locked into one focus - and you truly have mental blinders on, NOT GOOD!

The second design deficiency was that  the relay holding the alternator On-Line was provided current solely  by the battery - so guess what happened when the battery juice got too low to hold the alternator on-line?  Right "CLACK!!!!!"  followed immediately by all lights, radios, LEDS, panel going dark.  It gets even lonelier when the lights go out.  Had I two batteries - all of this would have happened further from my emergency airport in Salem, Al.

No, I have not added the second battery back in after the incident  - because in my particular case, the incident had nothing to do with one battery vs two battery  - it was a case of a mis-positioned switch which the pilot never recognized was the cause - until later on the ground, cleaning off the seat cushion.  The corrective action was to put a switch guard over that particular switch so it could NOT be accidently toggled incorrectly AND rewire my relay so that a dead battery would no longer prevent my system from using the power of a perfectly good alternator.

But, this is just my perspective - provided for anyone to glean what they wish from it - if that is two batteries, two alternators or what have you, then as always in this hobby, that is up to individual choice. 

 Just don't make the same dumb mistakes I made, we know how those turned out - advance the state of the art and make NEW mistakes {:>)

Oh, yes, the switch I accidently activated (I think I probably hit it with my foot getting out of the aircraft at the previous refueling stop) was one that enabled me to detach my battery from the alternator.  The thought at design time was that if my alternator ran-away with high voltage, I could isolate the battery from the alternator thereby preventing the battery from overheating/boiling and get to an emergency landing on battery power alone.  Seemed like a good idea at the time.

Ed

Edward L. Anderson
Anderson Electronic Enterprises LLC
305 Reefton Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com

I did the spread sheet with 17AH batteries and flying time. Add in Night, and no place to easily land.... two batties seem like a good trade off.  My biggest shock was the FORD style contactor needed 1Amp draw to remain closed.  Shutting down non essential, but leaving contactors, PDF, ECU and coils....   System draw is around 15 Amps. 17AH implies you'd have an hour, but at 15Amp draw... more like 30-40 minutes, hence two batteries as 1 hour flying time makes finding a landing strip a little easier. 

Tom