I appreciate your concise comments Eric.
I also appreciate the maturity you have shown by not responding to everything.
All the best,
Ahmet
SV8827
> From: [email protected]
> To: [email protected]
> Date: Wed, 1 Jul 2009 17:38:27 -0700
> Subject: Re: [Liveaboard] Wire Size
>
> <snip>
> However, since that long-wire resistor would now be
> in series with the "second" battery
> <snip>
> I guess you forgot about the charge/use switch?
> The long wire is only in series when charging. When the switch is in the
> 'use' position there is no difference between the wiring of the first and
> second batteries.
>
> Eric Thompson
> S/V Procrastinator
> South San Francisco
> [email protected]
>
> ----- Original Message -----
> From: "Ben Okopnik" <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, July 01, 2009 12:45 PM
> Subject: Re: [Liveaboard] Wire Size
>
>
> > On Tue, Jun 30, 2009 at 09:18:34AM -0400, [email protected] wrote:
> >>
> >> Of course, "small" is relative, but Yandina uses wire size and length to
> >> limit current through her Combiners to protect the relay contacts quite
> >> successfully.
> >
> > This, of course, does not prove much. I knew a fellow in California,
> > back in my racing days, who had built a steam engine into his Corvette:
> > he got great bottom-end acceleration, excellent fuel economy, and a pile
> > of bragging rights - but for some reason, most other Corvette owners
> > refused to follow his lead. Hard to imagine why...
> >
> > Ahmet's suggested approach will work in some sense - but will fail (just
> > like the above scenario) in many other important ways. For example, in a
> > real-life situation, a watermaker might draw 20A; /ceteris paribus/,
> > both batteries would normally have that drawn from each of them (since
> > they are in series.) However, since that long-wire resistor would now be
> > in series with the "second" battery, that battery will not be able to
> > supply its share - some of the voltage would drop across that resistor,
> > and in a high-current situation, every fraction of a volt makes a huge
> > difference. In fact, the drop may be enough that, as a percentage of the
> > total circuit resistance, the load (i.e., the watermaker) would get
> > essentially nothing from that battery.
> >
> > Even if we assume that the resistor is only part of the charging
> > circuit, there's still a fatal flaw in it: trying to charge that second
> > battery in parallel with the first would produce minimal or no results.
> > That resistor will not only limit the charge current that could possibly
> > flow into that battery - it will also create a voltage drop that would
> > prevent that battery from charging. E.g., 25' of 18ga has just under .2
> > ohms of resistance; assuming that the battery has an internal resistance
> > of about .1 ohms (a reasonable assumption, given the max no-regulation
> > currents I've seen in boat charging systems with large alternators),
> > this would cut the total current down to 48A - and drops 4.8 of that
> > 14.4V across that resistor (and dissipating some 70W across that wire in
> > the process. Barbecue, anyone?) Even if it doesn't catch fire, that
> > battery will never charge.
> >
> > Lastly, to counter the possible argument of voltage sensing at the
> > battery terminals and regulating based on that: if that is done with the
> > second battery, with its built-in voltage drop, then the first battery
> > (and indeed every other battery in that circuit) will be _over_charged
> > by that amount - instantly cooking any gel cells and severely
> > overheating any lead-acid types.
> >
> > In short (as the comic routine goes, "why did I say 'SHORT'?"), I
> > believe that adding any significant series resistance to a charging
> > circuit is a truly bad idea for many, many reasons - some of which I've
> > enumerated here.
> >
> >> While arc welding the arc produces enough heat to melt the electrode
> >> wire,
> >> however, when the electrode sticks to the weld pool and the arc is
> >> quenched
> >> the current is not enough to melt the wire.
> >
> > Norm, I don't want to sound disagreeable, but I do disagree: I happen to
> > be a certified welder, and the above is most emphatically _not_ true. A
> > "drag"-type rod, such as the very commonly used 6010, or the 7024, is
> > specifically intended for burying in the weld pool - and they continue
> > to melt just fine when they do. Many rods that aren't intended for
> > dragging can also be used that way, at their rated working current.
> >
> >
> > --
> > * Ben Okopnik * Editor-in-Chief, Linux Gazette * http://LinuxGazette.NET *
> > _______________________________________________
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