On Mon, 24 Jun 2019 10:42:29 +0100, trader_4 wrote:

On Sunday, June 23, 2019 at 8:06:32 PM UTC-4, Commander Kinsey wrote:
On Sun, 23 Jun 2019 15:22:13 +0100, trader_4 wrote:

On Saturday, June 22, 2019 at 7:30:59 PM UTC-4, Commander Kinsey wrote:
On Sat, 22 Jun 2019 16:16:30 +0100, trader_4 wrote:

On Friday, June 21, 2019 at 7:33:38 PM UTC-4, Commander Kinsey wrote:
On Fri, 21 Jun 2019 23:57:52 +0100, Rod Speed wrote:



"Commander Kinsey" wrote in message
news 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 the way batterys work, the battery voltage does change as its
charged.

That's determined by the alternator or charger.

Nope.

Yip. I can put any voltage I like across a battery's terminals. The battery then chooses how much current is drawn.

Correct, within reason and the physical limits of the battery. A battery
looks like an ideal voltage source connected in series with a low value
resistor.





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.

Its more complicated than that with the current going to the battery and the
battery is charged.

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.

No it doesn't even with a very crude battery charger.

For example, I'm currently keeping my car's battery topped up with a bench supply overnight. It's set to 13.8V, with a current limiter only to prevent overloading the supply. The voltage stays at 13.8V all the time, sometimes 100mA is drawn, sometimes up to 4A. The only way I or the supply can tell the battery is full, is by the current dropping to 100mA. But it's actually always full, as when 4A is drawn, that's going to a load.

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?

By checking the current actually being delivered to the battery.

I guess that may be true, if the car's computer has two ammeters and subtracts one from the other. But AFAIK, the alternator regulator only works by it's own current sensor. And that current could be going into the battery, or past it to the loads.

The voltage regulator actually senses VOLTAGE, which is why it;s called
a voltage regulator.

No it doesn't. It keeps the voltage at the correct level for charging, which is 14.4V for fast charge and 13.8V for trickle charge. It senses a drop in current to tell when the battery is full.

No it doesn't what? Of course the voltage regulator SENSES VOLTAGE because
otherwise it obviously can't regulate it.

It senses voltage so it can keep it steady.

No **** sherlock.

Voltage does not change when the battery gets full,

Yet you were the one telling us that it does.

No. All I ever said anything remotely like that was the alternator should change the charging voltage when it knows the battery is full. 14.4V is a fast charge, 13.8V is a trickle charge.

the current draw changes.

It doesn't target CURRENT.
And this is why you keep asking about how the VR knows how much current
is going to the battery vs how much is going to the car. It doesn't.
It doesn't care. It targets VOLTAGE and that's why it's called a VOLTAGE
REGULATOR, not a current regulator. Good grief, this is explained all over
the internet, not hard to find.

How can the battery change the voltage when it's kept steady by the regulator?

Who said the battery changes any voltage?

You did, I told you it watches the current so it can tell the battery is full, and you claimed it could do this by just sensing voltage

Find a graph of a battery being charged. Once it draws less than the maximum current the charger can provide, it stays at precisely the same voltage for the rest of the charge, and the current gradually drops. The charger senses this current drop and changes the voltage to different levels to enter the three charging phases.

Please learn to quote properly, I wrote the above line, not you. It should have two indents. This is basic computing ffs.

Maybe a smart charger does, the typical auto charging system, which is what
you were asking about, from everything I've seen does not. And Clare a
retired auto mechanic just told you the same thing.

Well my car does, and it's 2002.