>Did you happen to notice the ammeter while in the air. If it is showing a
>high rate of charge after a 'lap' or two around the pattern, then I'd look
>at your battery. A dying battery will pull a lot of current from the
>alternator. If this is the case, then all the current from the alternator
>will heat up the circuit breaker until it trips.
Batteries with a shorted cell change from a 12v to a 10v battery
and will indeed draw lots of extra current while being "charged"
from a 14v bus. Shorted cells result from a pile-up of flakey,
conductive material shed from the plates . . . which normally
fall harmlessly to the bottom of the cell cavity. Back in the
good ol' days, a deep pile of this flakey stuff would get too
deep and short a cell. There are a few, even more rare failure
modes of the separators between plates that can produce shorted
cells. Shorted cells in modern flooded batteries is extremely
rare and you woul notice it immediately in poor cranking performance
and dim lights with the alternator off. Further, a battery with
a shorted cell is likely to be so old that its useful service
life is long since passed.
Most (99.99%) of battery failures manifest themselves in poor
cranking performance and what appears to be a very rapid recharge
time after the engine starts. The time and amplitude of ammeter
"charge" indication after startup is directly related to the
battery's capacity and internal resistance. As capacity goes
down, resitance goes up and apparent charging time and amplitude
will both go down too.
In the instance under discussion, I don't belive this is the case.
>A friend of mine replaced the left position light after crunching into a
>hanger door. Got the part from the same make and model year complete with
>lamp. Flew several months before going at night. After that flight, he
>noticed the circuit breaker for the nav lights had tripped. Reset the
>breaker and thought nothing of it until the next flight. 'POP'
>
>He asked me to look into it. We pulled the wingtip and looked for chaffed
>wires; nothing. Looked at the holder, clean. Then looked at the lamp.
>Nothing note worthy. Looked at the right side. Nothing out of the
>ordinary their either.
>
>Then I noticed something; then left lamp was a 26 watt lamp. The right was
>a 20 watt lamp. Assuming that all nav lights were 20 watts in a 12 volt
>airplane, that makes 5 amps. The nav light breaker is a 5 amp breaker. Add
>6 watts to the mix and you 5.5 amps.
>The circuit breaker would not pop right away. It took about 15 minutes for
>it to get hot enough to trip.
The breaker was undersized . . . the minimum breaker size for nav
lites in a 14v airplane is 7.5 amps. Breakers and wiring used
to plumb the system should be selected with enough headroom
to INSURE NO NUISANCE TRIPS . . . I've written before about
breakers designed to nuisance trip in the form of a 60A breaker
on a 60A alternator . . . the writer has just identified another
one.
Bob . . .
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