nuckolls.bob(at)aeroelect
Guest
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 Posted: Sun May 17, 2020 5:55 pm Post subject: EXTERNAL PWR operations (follow up) |
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| Quote: | | Quote: | Or is it that the intelligent charger might not provide enough amps to close the
EXT PWR Contactor when plugged in through the EXT PWR Socket? |
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You used some words that beg clarification.
"Chargers" come in all sizes from the diminutive
wall warts that are characteristic of Battery
Tender Jr and Battery Minder (1A or so output)
up to battery shop beasts capable of hundreds
of amps to charge batteries or crank engines.
To be sure, the wall warts are probably best
referred to as 'battery maintenance' devices.
While they WILL charge a battery given sufficient
time, they should not be expected to close
a ground power contactor -AND- charge a battery.
A 'real' charger is will replenish a deeply
discharged battery in a practical period of time,
say overnight at most. This class of charger is
in the 5A plus class.
Any modern charger of any size should be expected
to included automatic charge shut-off and possibly
maintenance modes of operation that would prevent
subsequent damage due to overcharge.
I don't recall seeing any TC light aircraft fitted
with a ground power contactor that was crew controlled.
All are wired to close the contactor as soon as ground
power is plugged in and energized. The third, 'pilot
pin' in the mil-std ground power jack makes contact
only after the two fat-pins are engaged. This
feature prevents burning the pins by holding current
flow at bay until the plug is mostly engaged
and contactor is closed.
I have always thought that the pilot, not the
ground crew, should have control over when ground
power is applied. Additionally, wiring that energizes
the ground power contactor should include defenses
against over voltage and reversed polarity. I think
I recall some Cessna SE products having a diode
in the ground power pilot lead that would prevent
contactor closure on a reverse polarity situation.
The ground power receptacle should be explored with
the same diligence to FMEA as the rest of the
airplane. This exercise goes to both your understanding
of how to best use the feature as well as reduce
risk to the airplane.
Bob . . .
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