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From: ahmet erkan (no email)
Date: Mon Sep 01 2003 - 10:57:24 EDT
I agree with Lew, "This ain't rocket science" however I disagree with every
other conclusion. (Hoping we could disagree and still remain friendly.)
IMHO, if we are trying to establish a certain circuit breaker's reliability
to trip and not damage itself, this has been accomplished. (Occasional
tripping under overload for a test period of over a decade tells me this CB
can deal with the stresses it is subjected to in this application.)
If we are trying to figure out why Norm's CB's trip, the current carying
capability of the feeder may play a different role for the Windlass vs the
Inverter. The Inverter typically has a feedback loop that tries to maintain
constant output voltage when the input voltage sags, therefore the output
power remains constant. As an example, if the feeder wires to the inverter
drop 10% of the DC bus voltage, the inverter will require about 10% more
input current to maintain the output voltage, thus the CB current will
increase by 10% getting it closer to tripping. (Bottom line : Use heavier
wires and the same CB may stop tripping.)
On the other hand the Windlass may not have a feedback loop, thus it's input
current may decrease when the input voltage decreases, thus causing the
circuit breaker current to also decrease. (Bottom line : Use heavier wires
and the same CB may trip even faster)
The manufacturer of the Inverter needs to specify the maximum current the
device will cause in the input wires, during all possible operating
conditions including overload. We the user should use a circuit breaker that
is rated a little higher than the specified maximum. As an alternative, we
can install an interlock system that will disable other loads when a certain
load is turned on, thus prevent the overload from ever taking place.
The manufacturer of the windlass needs to specify it's locked rotor current
vs. input voltage and a CB should be used that is rated higher than the
specified maximum current. If more effort is needed from the Windlass,
heavier wiring and CB needs to be used.
IMHO it is an undesirable and potentially unsafe situation to rely on
mechanical contacts interrupting large currents on a regular basis. The
manufacturer of the windlass should provide some form of electronic sensing
and maybe timing of the overload condition and either sounding an alarm or
overriding the operator controls. (For mission critical equipment such as a
windlass there should also be an override for the protection circuit that
can be activated in the heat of a battle.)
Due to manufacturer's providing us with a lot of BS and inferior products,
if the frequent CB tripping is to be employed as an economical means of
protection, IMHO there should be heavy bare wires connected to the CB
terminals, the other ends should be bolted to large busbars with sufficient
surface area, serving as heatsinks. The insulated wiring can route the
current safely from the bussbar to the loads. If the CB contacts have
carbonized over the years of hard use and one day they decide to begin
arcing and dissipating large amounts of heat, the fire will be contained in
a non flammable CB enclosure and the heat will not conduct out of it through
the wiring. If there is nothing to burn such as wiring insulation the CB
will eventually melt up enough metal at it's contacts and the circuit will
open. Hot wires with burning insulation and no means to shut-off the power
is indeed a nightmare and I would not want any sailor to be subjected to it.
Have a good Labor day weekend,
Ahmet
>From: Lew Hodgett <>
>To:
>Subject: lv-ab: Re: Worthless Circuitbreakers
>Date: Sun, 31 Aug 2003 15:24:28 -0700
>
> writes:
>
> >Lew,
> >
> >I said very clearly in my message:
> >
> >Quote
> >The fact is that both of these breakers have tripped when they should
> >have,
> >with no apparent ill effects. The house buss breaker has tripped
> >several times
> >when I have called upon my anchor windlass to maximum effort, and the
> >breaker
> >feeding the Trace inverter regularly trips when someone tries to
> >operate two
> >high load galley appliances at the same time. These two breakers have
> >been in
> >operation for almost a decade and seem to work just fine.
> >Unquote
>
>The above indicates the following:
>
>1) If the feeder supplying the windlass has been properly sized, then the
>c'bkr tripping represents a nuisance trip which is not within the scope
>of proper operation.
>
>2) If the c'bkr is the proper size to protect the feeder supplying the
>windlass, then the feeder is undersized for the application.
>
>In any event, there is a problem.
>
>Similar logic applies to the Trace inverter; however, if the output of
>the inverter itself is placed in an overload condition, then there is a
>basic circuit design problem.
>
>As the popular saying puts it, "This ain't rocket science".
>
>
>Lew
>
>S/A: Challenge (Under Construction in the Southland)
>
>There are no problems, only varying degrees of Challenging Opportunity.
>
>
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