On 24/6/19 9:38 am, Clare Snyder wrote:
On Sun, 23 Jun 2019 12:04:19 +1000, Xeno
wrote:

On 23/6/19 1:45 am, Rod Speed wrote:


"trader_4" wrote in message
...
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?Â* 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?Â* That's determined by the alternator
or charger.Â* Let's say the charger/alternator gives out 14.4V
initially, to charge the battery quickly.Â* 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.Â* 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.Â* 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

But there is normally more than the one wire
at the the positive terminal of the battery.

Parallel circuits, so what?

and there is no monitor for what current
is going to the battery vs to the car load.

Wrong when there is normally more than the one
wire at the the positive terminal of the battery.

And Rod is talking computers,

Because thats what his car has.

so how did cars work prior to the 80s?

The regulator uses the voltage it sees which varys
with the load and the charge of the battery.

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.

Its more complicated than that with the voltage.

No it isn't.

It was that way from the early days and auto batteries charged fine.

Generators do it differently to alternators and we arent discussing
whether they charged fine or not, we are discussing what the
regulator does when the battery is fully charged so that it doesnt
boil off the water in the battery. Thats particularly important
now that most car batterys arent refillable with water anymore.

There may be some modern cars where they do monitor the current going
to the battery, maybe to save energy and increase fuel consumption,

It actually to avoid ****ing the battery by delivering
the same current to the battery when its fully charged.

but it's not necessary to keeping the battery charged.

That isnt what is being discussed either.

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

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

No it doesnt. Doing that would overcharge a fully charged battery.

and that has worked for 100 years.

Wrong again, generators do it differently to alternators.

Yes, no argument there. You mean like this;
http://mgaguru.com/mgtech/books/pdf/..._Box_Tests.pdf

Voltage and current control. They were pretty much on the way out by the
time I finished my apprenticeship.

With alternators, voltage is key.

You need to get with the times. Generators went out with button up boots.
A generator generally used a "3 unit regulator" Onewas the cut-out -
which is replaced by the diodes in an alternator. The alternator
cannot drain the battery attempting to "motor" itself like a
generator. The second unit was the current regulator, because a
generator is NOT self limitting. If you full feild a generator into a
dead short it will melt itesrlf down.

Some generators used only two bobbins. One was for voltage regulation,
the other the cutout. I used to see both types in the time of my
apprenticeship but by the time I finished, they were well and truly on
the way out. One of my teaching colleagues, an *old school* mechanic,
was an absolute wizard on those 3 bobbin regulators and also early
alternator systems. I did specialised automotive electrical training
under his tutelage and, through that, I developed more efficient ways of
delivering training in auto electrical aspects. All that was a long time
ago and my recall is getting rusty.

An alternator is self limiting due to it's higher stator resistance.It
will ONLY put out a certain amount of current into a load, regardless
of the resistance of the load. This is due to both the stator
resistance and the maximum flux of the rotor - so the current
regulator (actually "limitter" as it only controls the maximum output)
is not required on an alternator either. This leaves the voltage
regulator, which controls the feild current either linearly or by
"chopping" - or pulse width modulation. The more current flowing in
the feild the higher power produced - in volt-amps. As the current
changes, the voltage changes in reverse, for the same feild strength.
Higher current = lower voltage. By sensing and controlling the voltage
the current pretty much looks after itself - as the regulator
controlls the feild strenth by varying the feild current. It controls
the feild current by controlling the voltage impressed across the
feild coil.. As the engine speeds up, it requires less feild strength
to produce the same voltage.

Indeed, quite a simple system really.

--

Xeno


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