On Sat, 22 Jun 2019 20:06:16 +0100, 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.

Maybe they do that now. But that doesn't help me charging my battery at night with a seperate power supply. I'll just leave it at 13.8V, I don't need a fast charge, I just need it to remain charged as it's full when I get home. No matter what the load, if the terminals of the battery are kept at 13.8V, it should remain full.