C-172 landing light switch

"mikem" wrote in message
...

first, a std 4509 landing light draws about 8A. Check to see if some
has installed Q4509 or some other non-standard sealed beam.

Good...

second, all things working normally, if the total load exceeds the
total generation capability, then the difference is supposed to come
from the battery (as long as it has some residual charge in it). In
other words, if the total bus load is 40A, but your generator is capable
of delivering only 30A, then the genny should be up to delivering its
full rated 30A output all day long. It shouldn't care what the total bus
load is... (turning on extra load should not trip the genny breaker)

But after that extra load (coupled with low engine RPM), has dragged down
the battery voltage, all bets are off. The regulator might then put more
currrent to the field (this current may be passing through that breaker),
causing the alternator current to drasticly increase.


If the genny blows its breaker, then either the breaker is bad (more
on this later), or someone has dicked with the current cutout relay
in the generator regulator in a misguided attempt to get it to
deliver more output. The current cutout relay must be set lower than
the Gen breaker rating.

As breakers age, they can develop internal resistance in their contacts.
The heat produced by the increased contact resistance adds directly to
the heat produced by the little built in heater (that is why they are
called a thermal breaker), and the breaker will trip at currents lower
than what is engraved on the button...

Another possibility is a small amount of resistance where the wires connect
to the breaker, this will cause heat (Power = I ^2 X R) which will have the same
effect as bad contacts in the breaker. You find this by feeling for excessive
heat when there is current flowing through the breaker. The breaker may
actually make the panel noticably hot, or you may have to feel behind the panel
(taking all necessary safety precautions).

Vaughn (Licensed Electrician, Electronics Tech, but NOT an A&P)




You need to find an A&P who understands electricity (not many of them do).

MikeM, PhD EE
Skylane '1MM
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