> this morning I jump started our van [...] This brought to mind a
> question I have long had about jump starting. The battery in my
> car starts my car immediately. But when I connect that same battery
> to another car (the one I am jump starting), that car will not start
> immediately... I need to wait several minutes
>
> 1. The resistance of the cables is too high to deliver the needed
> current to start the dead vehicle.

It's the resistance of the cables, the resistance of the clamps,
the cleanliness of the battery posts, and the comparative size
of the batteries & supply vehicle charger & taret vehicle starter.

I carry cables made with size 0(?, same size as my welder's ground
wire) copper wire & top-notch clamps.  Clamps have strong springs.
When I put the clamps on -- both ends -- I wiggle them around to
ensure that the surface oxidation is broken and there is good
contact (to battery terminal or to heavy frame member).

With my old V8 Surburan supplying current, I can immediately crank
any new politically-correct car. If target vehicle won't crank, it
is a poor connection at the clamp ends.

> (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.)

They are.  Look at car parts stores that cater to professional
vehical repair stations.  That means not Autozone, not Pep Boys,
not O'Reilly/Kragen.  However, you may be able to special order
decent jumper cables from them.  Remember, if you want quality,
you have to pay for it.

You can also get raw cable & clamps for jumpe rsets from welding
stores, aviation supplies, industrial supplies, etc.

> 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)?

As others have mentioned, there's the issue of vented hydrogen.

There's also the issue of the cable resistance from the target
vehicle's battery negative terminal to the engine block (and
thence to the starter).  When trying to jump start, it helps
to minimize losses everywhere you can.

						Lee Jones
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.