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how much time is left when the alternator fails.<
Some time ago in the Lancair Network News we
reported about a friend of mine that had dual
electronic ignition in his 320. One side was run
from the main power distribution system and the
other from a small battery isolated by a diode
form the aircraft's main distribution system.
His main battery blew up due to an overvoltage.
The isolation diode shorted out putting the isolation battery in the position of trying to run not only the electronic ignition but
also the entire aircraft electrical load.
The overvoltage forced a lot of electrical systems like his HSI and engine instruments to fail and the little battery
was able to get the aircraft back on the ground
without an engine failure but just barely.
Isolated dual electronic systems are OK.
However, if you plan to charge both batteries
from the same alternator, be careful in how you
design the isolation. In the above case the isolation diode was designed to handle 30 volts but this was not enough when the 14V alternator ran away.
Another problem with isolation diodes is that
they ususally fail in the shorted mode.
My next project will be to put one electronic
ignition on my 360 avoiding the isolation issue altogether. Jim Frantz
LML website: http://members.olsusa.com/mkaye/maillist.html
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Please send your photos and drawings to marvkaye@olsusa.com.
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