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 * _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard To subscribe send an email to [email protected] To unsubscribe send an email to [email protected] The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
