nuckolls.bob(at)aeroelect
Guest
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 Posted: Sat Feb 27, 2010 9:16 pm Post subject: Clearing some away some fog and fuzzy logic . . . |
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At 10:43 AM 2/26/2010, you wrote:
| Quote: |
The main issue in this debate seems to be whether to use fuses or
circuit breakers. Like many decisions in life, there is more than
one way to accomplish a goal. One way may have certain advantages
over the other way, and visa-versa. Many times the decision boils
down to a matter of personal preference; and I believe that is the case here.
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It's always a personal preference but it's not
always a matter of 'let's take out a 5A breaker and
put in a 5A fuse'. There are even instances where
two 5A breakers can exhibit SIGNIFICANT differences.
It's not even a debate about which is better or
preferred but a reminder that what ever device
is being considered, confident compliance with
design goals may goe far beyond current ratings.
Some people might argue that fuses will blow quicker than circuit
breakers will trip, thus offering better protection. Although
technically true, I do not think the time difference is significant.
It's not necessarily better but it IS different.
The time-to-trip dynamics for the full gamut
of protective devices is huge . . . if you're
just protecting the wire to gear down indicator
LEDS, the differences may not be significant.
But as soon as the load offers high inrush or
transient characteristics like incandescent landing
lights, pump motors, pitot heaters, confident
application of the chosen device demands understanding.
One way to avoid nuisance blowing of fuses is to use a larger
size. For instance, an avionics manufacturer might recommend using a
1 amp fuse. If you use a 3 amp fuse instead, there will be a lot
less chance of it blowing.
I counsel rejection of the off-hand up-sizing
just to hedge one's bets. The prudent designer
doesn't wager, he strives for the sure thing.
| Quote: | Quote from Bob,
> "discussed, researched, and demonstrated not to be true."
End Quote
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| Quote: | I am taking Bob's side here. The technician is basing his statement
on rumors. Bob has done experiments with expensive lab
equipment. I trust his work. Even if the technician is correct
(which I doubt), I would rather ruin an alternator than have an
over-voltage condition ruin thousands of dollars worth of avionics.
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It's not about gathering followers into the
camp of any particular individual. We're not running
for office. It's about the physics of simple-ideas,
about lessons-learned, about failure-tolerant design
based on logic.
| Quote: | Although the technician is highly critical of Bob's
recommendations, I do not take his statements as being a personal attack.
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I guess you've not been hanging around this List
very long my friend. The "technician" in another
life claims much in the way of qualifications for
his opinion . . . including engineering degrees.
He was asked to leave the List some years back
simply because he proved incapable or unwilling
to comport with list decorum. See:
http://www.aeroelectric.com/articles/gmcjetpilot.html
But since ALL our writings have been archived for
the future, I continue to be asked about certain
of his assertions years later. What was that we
read about 'sins of the fathers'?
| Quote: | Still, he was expressing his opinions as fact and pooh-poohing
Bob's, which is not a nice thing to do. If I say something that
others disagree with, it is OK to tell me, as long as it is done
diplomatically. LOL
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I quite agree as do the vast majority of the List
members. This particular circumstance may well
bubble up to the surface for years to come . . .
Bob . . .
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