nuckolls.bob(at)aeroelect
Guest
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 Posted: Sat Apr 04, 2009 5:12 am Post subject: Effects of Battery Disconnect with Good Alternator? |
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At 06:47 PM 4/3/2009, you wrote:
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In testing we've done in the lab and in the aircraft on a "standard"
and basic system, disconnecting the battery causes voltage
fluctuations which very quickly trip the OV circuit (>16v). YMMV.
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Yeah, thanks for reminding me.
When the individual responsible for setting voltage
regulator dynamics is fine tuning their creation
on the bench, they'll have to trade off regulation
response time with regulation stability. There
are some regulators in the wild wherein the author
went for fast response and lost some stability
that was mitigated by the presence of a battery.
I had to make the same choices on the B&C LR and
LS series regulators 20 years ago. As I recall,
I was more interested in stability . . . we
tuned the response dynamics for a slightly
under-damped response to moderate load dump
with battery connected. See:
http://www.aeroelectric.com/Pictures/Curves/damping_ratio.gif
The top response curve represents an "under-damped"
response which can be fast/accurate but prone
to "jitter". The bottom curve is "over-damped"
which offers great stability in constant load
situations but poor response to changing loads.
The middle curve illustrates the idealized response
that overshoots slightly in response to a load
change but damps quickly after the single
overshoot. I don't recall exploring system performance
sans battery.
But Marc's observations are right on point. Virtually
nobody designs for alternator-only operations. This
is considered a failure mode that begs for correction.
Only the aircraft guys are inclined to do failure mode
effects analysis and consider loss of battery in crafting
Plan-A, Plan-B, Plan-C, etc.
I will suggest that a second E-bus feed directly from the
battery for combined with well considered preventative
maintenance is the best hedge against loss of battery
contactor. This takes the sans battery performance of
the alternator/regulator out of the equation.
Bob . . .
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( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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