My voltage alarm is set to go off at around 13.5 volts.  This is higher than a fully charged battery.  In other words, alarm goes off the instant that the alternator fails.  System voltage is about 14.2 volts under normal conditions.

 

It is amazing that people with a complete understanding of how critical electrical system is on an EFI aircraft engine would install an alarm light so small or positioned in such a way that it would not be noticed.  I would have to be brain dead not to notice mine.  I have had one alternator failure which occurred almost immediately after engine start (this seems to be common).  The alarm went off and I taxied back to the hangar.  My reaction was not to install another 30 to 40 pounds of electrical stuff on the aircraft.

 

Tracy

George,

 Most of the motorcycles will still show at least 11 volts while cranking and those are small batteries. They will jump back up to at least 12.5 after cranking. I agree that 9.5 volts is almost totally dead for practical purposes. Most battery based systems will have trouble at around 10 volts. Use a backup battery and a changeover system with any electrically based system. The EXP Buss (I think) is sold by the anywhere map people. Makes it very easy to set up a battery backup system and still charge both. I think Eggenfellner also sells them. Good looking product, a good friend has one.

 For battery info go to the Yuasa web site. In the technical section they have a excellent do's and don'ts of battery operation. There is also a good description of the different battery types and their discharge rates. Good info to know about this VITAL system part!

Bill Jepson 

 

In a message dated 2/15/2005 11:34:28 PM Pacific Standard Time, lendich@optusnet.com.au writes:

Bill,
What would you expect the battery to show under starting load.
George ( down under)

>
> >  I suspected a charging system failure immediately and checked the
> >battery voltage in the SDS monitor. This read 9.5 volts so I knew then
that
> >we had a charging system failure. At the time, I was not worried about
> >making it to an airport, assuming that the alternator had failed just in
the
> >last few minutes and believing that I had 20-25 minutes of battery power
> >remaining. In fact, it is likely that the alternator failed soon after
> >takeoff from Springbank but I did not notice signs of the failure until
the
> >battery was well over half dead.