On 25/6/19 1:01 am, Clare Snyder wrote:
On Mon, 24 Jun 2019 12:13:22 +1000, Xeno
wrote:

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.Â* Cars used voltage regulators for better part of a century and
they are simple electronics which is well understood.Â* And, AFAIK,
that is STILL how it's done, all the FUD here notwithstanding.Â* 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.



GM and Honda are examples of charging systems that use a device to
monitor the battery voltage and current flow.

GM uses a battery sense module on some applications, which is
typically mounted to one of the battery cables. The sensor module uses

My Toyota has one of those on the positive battery cable. It is an
inductive sensor.

a Hall Effect sensor, which provides a 128 HZ PWM signal to the BCM
(Body Control Module). The sensor stays powered up even when the key
is off, so the BCM can identify parasitic drain.

Honda applications use an electrical load detector (ELD), which is
typically located in the underhood fusebox. The function of the
electrical load detector is very similar to a battery sense module.

Yes, it is on the main current path to the electrical system. Due to its
location, it cannot sense starter current but that is no big deal since
that is not its purpose anyway.

The PCM supplies five volts to the electrical load detector. The
electrical load detector grounds the circuit, providing a voltage
signal between 0.3€“4.50 volts to the PCM. The higher the voltage, the
lower the charging system output, while a lower voltage indicates a
higher charging system output


GM and Ford use a different strategy, where the computer monitors
feild current (actually feild voltage, but the voltage across a fixed
feild resistance yeilds a current measuremnt and by computation
deduces what the output current is.

There are a lot of different computer controlled charging strategies out
there. I am not well up with them since I retired 18 years ago and lost
access to all the factory technical information I was once privy to.

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)