|
|
|
|
|||||
|
||||||
From: Kevin Redden (no email)
Date: Mon Jan 03 2005 - 10:18:23 EST
> -----Original Message-----
> The January issue of Professional Boat builder has an article by Nigel
> Calder on the subject of Hybrid power propulsion.
> There is a side bar on regulatory and safety issues. In it he says:
> "it is sometimes suggested that 120VDC is more dangerous than 120VAC".
> He then goes on to say that he does not know if these fears have any
> scientific foundation. Then he quotes someone from the Glacier Bay
> company who indicates that DC power is less dangerous than AC. HUH???
Arild,
Your post brings up a point that I've noticed for years. Nigel Calder seems to
be a boater with a gift for generating written words - and for making those
words sound authoritative, regardless how correct they are!
If we look at the books he has written, and ASSume that he is an expert on each
of the subjects he writes about, he would have to be an incredible genius. The
subjects include:
. Diesel Engines
. Marine Electronics
. Geology & Environmental Engineering
. Navigation
. Marine Refrigeration
. Astrophysics & Einstein's Theory of Relativity
. Military Weapons Development
. Astronomy
. Weather
. Cruising Guides
. Politics of Nuclear Weapons
Taking a look at that list, you can see that Nigel could not possibly be an
expert in all of these topics, and as such, his information must be a collection
of tid-bits he's picked up and then presenting as fact. As such, I don't pay a
lot of attention to what he writes. I want the books I read to be written by an
expert in the field involved, not by a professional wordsmith with little
expertise in the subject he is writing about.
To address your question about AC vs. DC, I will defer on one part of the
question, but comment on another. I've heard conflicting claims about the safety
of AC vs DC VOLTAGE issues. This debate has been around since the days of Edison
(DC) and Westinghouse (AC). For a given voltage and current supply, is DC more
dangerous than AC - there are claims both ways.
Where there is indeed a real danger with the DC systems we routinely see on
trawlers is in their close to unlimited amperage capabilities! The short circuit
current potential for a large house battery bank is phenomenal! In this case,
our DC systems are far more dangerous than the average AC circuit which is
circuit breaker protected to reasonable current flows. Many boaters think that
because their DC system is only 12 volts, the danger is low. Unfortunately, what
they are ignoring is that a short circuit (as caused by a watch, ring or dropped
screw driver) on the primary DC conductors could have the ship's batteries
feeding literally thousands of Amps through the short, causing the vaporization
and explosion of the material causing the short. This is extremely dangerous,
but generally ignored by many boat owners.
What you said about the DC backup power room for the power station being a
dangerous place, you were absolutely right. I remember working in the battery
rooms of large data center UPS systems. A short across the buss bars would have
been catastrophic, so extreme care was needed around those large battery banks.
Just because the voltage is low, a battery bank should not be underestimated -
it is the huge current available that can get you.
When I work around the batteries on boats, I make sure rings and watches are
removed, and rubber mats are used over the terminals to minimize the chances of
an inadvertent short.
DC power is safe? - Not in my book - regardless what 'Nigel the
Expert-on-Everything' claims!
Kevin Redden
MS-III Dream Weaver
Westfield, NJ
www.BoatMoves.com
_______________________________________________
http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering
To Unsubscribe send email to
Include the word Unsubscribe (and nothing else) in the subject or body of the message.
Trawlers and Trawlering, T and T, TrawlersandTrawlering, and TandT are trademarks of Water World International. Unauthorized use is prohibited.
|