On Sun, 23 Jun 2019 07:26:22 +0100, Xeno wrote:

On 23/6/19 5:55 am, Commander Kinsey wrote:
On Sat, 22 Jun 2019 20:44:15 +0100, trader_4 wrote:

On Saturday, June 22, 2019 at 3:06:28 PM UTC-4, Rod Speed wrote:
"Commander Kinsey" wrote in message
news It would have to monitor the current going into the battery, by
having at
least two ammeters,

Just two cables from the battery positive terminal, one to the
alternator
and one
to the rest of the electrical system and measure the voltage drop over
those.

or have all the positive wires join somewhere

They do, the positive terminal of the battery.

and measure the branch off to the battery.

Just subtract the current to the rest of the electrical system
from the current going from the alternator to the battery
terminal. That gives you the current going into the battery.

When you have an actual credible cite that describes this alleged
system, post it. Until then, all you are doing is making crap up on
the fly.

I can believe him, I've observed my car's alternator change from 14.4V
to 13.8V after it's been running for a bit, so it must know the battery
is full.

Like claiming that all cars have more than one wire to the battery
positive terminal.

I've never seen one that doesn't. Usually I see one for the alternator,
one for the starter, and one for everything else. Why would you have
only one? These are high currents, best to connect things directly.

The starter cable is irrelevant in this equation since there will be *no
current flowing* unless the starter is operating. If the starter is
operating, then there will minimal output from the alternator so, in
that situation, the alternator is irrelevant. So, it the engine is
running and the battery is fully charged, the *battery* is, for all
intents and purposes irrelevant since alternator current will, for the
most part, be flowing from B+ on the alternator, bypassing the battery
and flowing to those loads that require it. The alternator is, in
effect, wired in parallel with the battery.

I guess it depends on the physical position of the main components. In every car I've had (about 10 of various makes), the alternator, starter, and main fusebox are nowhere near each other, so there would be no point in using the same cable for more than one of them. The best idea is to have the shortest run from the battery to each of them, that way you lose less voltage.

Or that cars use the resistance of the large gage cable to measure
current. You just pulled that one from your ass, it's rather unlikely
for some obvious reasons. But hey, you claim that's how it's done,
provide some references.......

I do hate it when people say "for obvious reasons" - they are never
obvious to anyone else.

That is precisely how you measure current, by a voltage drop across a
known resistance.

Correction, that is how you *calculate current*. The issue is that you
need to *know* the resistance.

I'm quite sure the designer of the car knows what wire was used.

An ammeter will measure current directly by being placed *in the
circuit*, with or without a shunt resistor.

And they certainly don't want to add more resistance
to something trying to carry 100s of amps.

Ammeters have extremely low resistances so have minimal effect on a
circuit, especially general automotive ones. If you need to measure a
higher current than the meter is capable of handling, you use a shunt.

Or a known resistance already in the circuit, like the feed wire.

I guess they could also use
an amp clamp, but that would cost more.

Amp clamps are cheap. Have a pro one here somewhere.

How much did it cost? Now think of that price being added to a car. And bear in mind it has to be able to report the readings to the ECU.