nuckolls.bob(at)cox.net
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 Posted: Tue Oct 14, 2008 4:39 am Post subject: SD-8 Failure in Z-13 |
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Bob. I have used your Z-13 "All Electric Airplane on a Budget" schematic as
the basis of the electrical system on my Long-Ez. I recently returned from
a flight to find the Aux Alt Off/On switch to be ON, whilst the DC Power
switch was on, the battery contactor closed and the main alternator
supplying the power. On checking the Aux Alt system subsequently I have
that it does not work. To help me with the fault finding, are there any
parts that could have shorted out/been fried? Is there a procedure for
checking out the 'dynamo' and its circuit? Any help would be great. Many
thanks Bob.
First, it's not an automatic no-no to have the small
alternator turned on at the same time the main alternator
is on . . .
When two alternators run in parallel, the alternator
with the LOWER regulator voltage set-point will
relax and the one with the HIGHER set-point will
attempt to pick up all system loads. If the 8A
machine had the higher set-point, then it would have
been running all-out for the duration of your flight.
The main alternator would have picked up the difference
between the SD-8 output and system loads as the bus
voltage sagged.
This is not an automatic recipe for alternator failure
but if the rectifier/regulator were inadequately
heat-sinked, it could have caused internal damage
at some point in the flight.
That's about the only part of the SD-8 system that's
vulnerable. Check with a voltmeter that you have AC
voltage coming in while the engine is running and that
the disconnect relay is closing.
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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