> Let's think about that a bit Roger.
>
> The starter and alternator in every highway vehicle
> manufactured in the past 40 years is grounded to the engine
> block or other major engine component. The battery negative
> primarily connects to the block, and always has at least one
> smaller (number 8 or larger typically) lead to the chassis
> for accessories.
Certainly true, up to perhaps 5-10 years ago. I'd not be so sure these
days. Charging, ignition, and engine control systems are always changing.
More and more, they're using solid state point of load switching kinds of
schemes too. The copper cost is a significant part of a car cost (especially
with all the accessories).
As more cars go to 46(?) volt DC systems with auxiliary loads at 12VDC, it
will be even more strange.
I suspect that installing radios in cars will be more and more complex in
the coming years. It may well be that the optimum solution will be a
dedicated battery for the radios and a galvanically isolated charger that
runs off the car's accessory system (aka cigarette lighter).
>
> How many vehicles have you seen where major welded
> sheetmetal components just fall off, outside of train/auto
> collisions or Yugo's of course??
I would say that a significant number of modern cars have body panels that
are not electrically bonded to the rest of the panels. There's a definite
trend to providing explicit power return wires from big loads, rather than
using the chassis as return. Especially if you're using "low side
switching".
>
> Why would a bad weld or even a dozen bad welds would cause a
> problem and allow a major chassis component to electrically
> float?
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