"Xeno" wrote in message
...
On 24/6/19 9:45 am, Clare Snyder wrote:
On Sun, 23 Jun 2019 12:05:52 +1000, Xeno
wrote:

On 23/6/19 1:57 am, Rod Speed wrote:


"trader_4" wrote in message
...
On Saturday, June 22, 2019 at 6:00:41 AM UTC-4, Brian Gaff wrote:
Yes indeed, the nominal output of an alternator can be as high as 15
volts,
but even a fully charged car battery is only 13.8v as far as I know
and
these days, I'm sure the direction of current flow and voltages are
monitored very well by the computers. In the old days it was a bit of
a
black art just relying on the ability of the alternator or dynamo in
the old
bangers.

Nonsense. Cars used voltage regulators for better part of a century
and
they are simple electronics which is well understood. And, AFAIK,
that is STILL how it's done, all the FUD here notwithstanding. Some
cars may have something more elaborate, but it's obviously not
required
to keep the battery correctly charged, which was the OPs question
about
charging.

No it wasnt, he asked about changing to a trickle charge when the
battery
is fully charged.

Battery chargers do it automatically - if they are decent.
Alternators too do it automatically.
SOME chargers - and some vehicles that use the computer to control
charge, use a "3 step" algorythm which uses constant current to "bulk
charge" the battery to a certain level, then switch to constant
voltage untill output current drops below a certain point where it
switches to "float charge". Not COMMON on cars, but getting pretty

A car charging system is unlikely to ever really *need* a float charge
mode since it has to deal with other electrical system loads as well as
the needs of the battery. That and the type of use the car battery gets
adds a layer of complexity to it all that I can't see is really warranted.
A battery charger, on the other hand, has to deal only with one load, the
battery.

common on higher end chargers to prevent overcharging and gassing of
the battery when left on charge. The old service station type chargers
had a simple timer to accomplish this - and some of the later ones had
a combination - when charging voltage exceded a certain point it would
charge for anothe X number of minutes before shutting down.



Automotive charging systems that actually sense current are
EXCEDEINGLY RARE.

I've never seen one.

You just have. His Renault clearly is reducing the voltage once
it has decided that the battery is fully charged and that can
only be by sensing the current that the battery is taking.