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nuckolls.bob(at)aeroelect
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 Posted: Wed Feb 04, 2009 1:39 pm Post subject: Checllist Procedure for Z-13/8 Power Distribution |
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At 01:41 PM 2/4/2009, you wrote:
| Quote: | I'm using the Z-13/8 Power Distribution diagram in a Glastar with dual Dynons.
The FlightDek D180 is connected to the Main Bus and the EFIS D100 is
connected to the Endurance Bus. Each unit monitors it's bus voltage.
In normal operations I fly with the MASTER switch and AUX ALT switch
ON and the ALTERNATE FEED switch OFF. I have experience no problems
with this configuration.
I recently implemented an checklist procedure to test the power
distribution circuit and alternators on startup before taxi. After
starting the engine and checking that the MASTER and AUX ALT
switches are ON, I check that the voltage on the EFIS is .6 V less
than the FlightDek.
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There is no value but also no harm in running both alternators
at the same time. The Aux alternator produces no useful output
at engine rpms typical operations during your pre-flight checklist.
| Quote: | I then switch the ALTERNATE FEED ON and check that the EFIS voltage
is the same as the FlightDek (over 14 V).
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This is a valid check of normal feedpath diode (shows it is
not shorted).
| Quote: | I then switch OFF the MASTER and check that the FlightDEK voltage
is 0 V and the EFIS voltage remains above 13.5 V.
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Confirms good diode but depending on e-bus loads and
engine rpm during this test, you may have trouble supporting
the e-bus above 13.5v
| Quote: | I then turn the MASTER back ON and the ALTERNATE FEED OFF and I'm
ready to taxi. This procedure appears to be working fine and I have
experienced no problems in flight.
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The Aux Alternator was never intended to be used
in normal flight. Under certain day vfr loads, you
could have a main alternator failure and not know
it if total loads are within capability of the SD8
to hold the bus up. Recommend that the SD-8 not be
ON for normal operations.
| Quote: |
When I reviewed the flight log from the FlightDEK however I
discovered that I was inducing a significant negative (MASTER OFF)
and then possitive (MASTER ON) current (over 200 amps.) for a short
period of time in the main alternator when I'm performing this test
procedure. Will this damage the alternator?
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What is a "short period of time"? I'm skeptical
of this value because your alternator is not
capable of sourcing 200A nor is it capable of being
a 200A load. This may well be a flaw in the signal
conditioning for your data acquisition system.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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Norm Biron
Joined: 04 Feb 2009
Posts: 7
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| Posted: Wed Feb 04, 2009 3:28 pm Post subject: Checllist Procedure for Z-13/8 Power Distribution |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Bob,
Thanks for your reply. I'll take your recommendation and not turn on the SD-8 alternator in normal operations. My initial thinking for turning on the SD-8 alternator in normal operations was to maintain power on the main and endurance buses and continue my flight, if the SD-8 could maintain the load, without knowing that the main alternator had failed. My startup checklist was developed to discover the problem on the ground before the next flight.
When I'm making the power distribution tests in the startup checklist, the only loads on the alternator is the battery, battery bus, and the endurance bus EFIS. The SD-8 has no problem sustaining the 13.5 V at 1000rpm.
The Dynon log is set up to samples data every 10 seconds, so the short period of time is less than 20 seconds. I agree that the amperage values may be a signal conditioning problem, but I still believe that main alternator is seeing a substantial transient during this test. Can this damage the alternator?
Norm
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