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 On Sat, 22 Jun 2019 15:28:21 +0100, trader_4
wrote:

On Friday, June 21, 2019 at 6:48:31 PM UTC-4, wrote:
On Fri, 21 Jun 2019 23:15:21 +0100, "Commander Kinsey"
wrote:

On Fri, 21 Jun 2019 22:57:44 +0100, Max Demian

wrote:

On 21/06/2019 21:19, Commander Kinsey wrote:
How does a lead acid battery charger (or car alternator) know
when
to
switch to trickle charge?* I can understand it noticing a
drop in
charging current if the battery is on its own, but what if a
random
changing load is connected, as there is in a running car?

The voltage perhaps.

Why would the voltage change?* That's determined by the
alternator or
charger.* Let's say the charger/alternator gives out 14.4V
initially,
to charge the battery quickly.* It'll just sit at 14.4V forever,
providing the charger can give out enough current to charge the
slightly flat battery and power any connected loads.* If the
battery
had no loads connected, it would take a lot less current when it
became
full, but the voltage would stay the same.* If the charger
monitored
the current it was providing, how does it know if the battery is
still
charging at 10 amps, or if the battery is full and there's a 10 amp
load?

Not really true with anything but the most primative regulator like
you might see on an old outboard. Voltage is regulated somewhere
between 13.x and 14.x, not just reflecting what the alternator
can do
against the load.
Rod is right, they look at current from the alternator

Every car I've seen, the the alternator, the battery and the
rest of the car are tied to one point and there is no monitor
for what current is going to the battery vs to the car load.
And Rod is talking computers,
so how did cars work prior to the 80s? They didn't have a computer
didn't monitor anything other than the voltage regulator maintained
a constant voltage of ~14v while the car was running.* It was that
way from the early days and auto batteries charged fine.

There may be some modern cars where they do monitor the current going
to the battery, maybe to save energy and increase fuel consumption,
but it's not necessary to keeping the battery charged.

I doubt it saves much energy.* Charging a lead acid at 13.8 to 14.4V
continuously, wastes **** all power.* More likely it can charge at a
higher voltage to begin with to make the battery full quickly, then
pull
back to trickle when needed.* Handy if you make a habit of using a
lot of
accessories like lights when the engine is off then need it charged
quickly when you drive for 10 minutes.** Or if like me you drive
for 100
yards at a time and are using the starter a lot (or have one of
those stop
start engines).* Older cars would run out of battery if you did
lots of
short journeys, as there was no fast charge.

There is nothing they can do about the load so they don't give a
****
about the
lights.* The regulator just watches alternator current and cranks up
the voltage to keep it up.

That's rather bizarre.* The alternator monitors current?* So, what's
the correct current that it's targeting?* 2 amps, 20 amps?* 70 amps?
The current depends on what loads are on and the alternator doesn't
know that.* Seems to me it keeps the system VOLTAGE at ~14V and that
has worked for 100 years.

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.

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.

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.

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

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

--

Xeno


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