At 12:54 PM 5/15/2012, Eric Kort wrote: >1. The resistance of the cables is too high to deliver the needed >current to start the dead vehicle. (It seems if that were true, >someone would be out there selling uber-cables that don't have this >problem, but I don't recall seeing such cables.) Yep. The starter needs significant current to operate. >2. The dead battery is a low impedance current sink while it is >charging, sucking away the available current from the higher impedance >starter until it is charged enough to start the car on its own. Also Yep. A discharged Lead-Acid battery that is otherwise in good=20 shape (not sulfated) has an extremely low impedance and will consume=20 just about as much current as you can give it. That causes=20 significant voltage drop in the jumper cables, which contributes to (1) abo= ve. >And while we are on it, why does the owner's manual suggest connecting >the negative end of the cable to the engine block of the dead vehicle >(doesn't the engine have continuity with the negative terminal on the >battery--making it simpler from a procedure point of view to just >connect the battery terminals on both vehicles)? A battery that is being charged at a high rate gives off Hydrogen=20 gas. You want to keep sparks as far away as possible from that gas. I had an unfortunate incident during High School where I was in close=20 proximity to a rather large car battery that was being charged. The=20 charging lead became dislodged somehow and the battery promptly=20 exploded. Luckily, the lab was in fairly close proximity to the Gym=20 showers and I was quickly dragged to where I could be rinsed off. No=20 damage done, other than to clothing. Large holes did appear . dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .