On Mon, 24 Jun 2019 16:33:08 +0100, TMS320 wrote:

On 23/06/2019 23:55, Commander Kinsey wrote:
On Sun, 23 Jun 2019 17:27:09 +0100, TMS320 wrote:

On 22/06/2019 22:58, Commander Kinsey wrote:
On Sat, 22 Jun 2019 17:03:08 +0100, TMS320 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?

It doesn't.

Mine does, if I start my car when the battery is say 80% full, the
voltage will be 14.4V. After a while, something causes that voltage to
drop to 13.8, because something knows the battery is full and should no
longer be charged at a high rate.

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?

Ohm's law.

Explain how an alternator or charger can use ohm's law to distinguish
between:

To determine current, measure the voltage across a series resistor, duh.

Why didn't you wait until I'd finished?

You asked.

No, I said "explain.... distinguish between:" and before I'd listed the two things, you interrupted.

1) A car battery which is full, with a load of 10 amps connected to it,
like two headlights.
2) A car battery with no load, which is not full yet and draws 10 amps
for the charge.

Two resistors?

Yes that would work, but not if it has no external sensors (as in
external to the alternator).

An alternator is not simply two wire power output. The electronics on
the alternator would be to keep everything within acceptable parameters
but fine control comes from the ECU.

So there are external sensors.