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Commander Kinsey Commander Kinsey is offline
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Default Lead acid battery charger (or alternator) switching to tricklewith load present?

On Sat, 22 Jun 2019 00:26:13 +0100, Rod Speed wrote:



"Commander Kinsey" wrote in message
news
On Fri, 21 Jun 2019 23:39:34 +0100, Rod Speed
wrote:



"Commander Kinsey" wrote in message
news On Fri, 21 Jun 2019 21:54:38 +0100, Rod Speed
wrote:

Commander Kinsey wrote

How does a lead acid battery charger (or car alternator) know when to
switch to trickle charge?

From the current the battery takes.

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?

You just look at the current going to the battery. The variably
loads like with lights isnt supplied by the battery when the
engine is running, its supplied by the alternator.

But how can the regulator on the alternator possibly know the current
it's
passing to the battery is going into the battery and not going straight
across to the lights?


The computer knows whats going to the battery and you can see that with
an ODB2 dongle.


My dongle only lists faults.


Because it's a steaming turd with wheels frog car.


Which should adhere to the ****ing OBD standards according to the frog's own EU regs!!

And a very basic OBD reader I bought to determine why a warning light was on.

Most show all sorts of things.

If you look at the battery in your car, there are two or three thick
wires
coming off each terminal. One will go to the alternator, another to the
fusebox for all the lights etc.

And it's the voltage across the one going from the alternator to the
battery that allows the computer to know how much current is going to the
battery.


Bull****.


We'll see...

How could it possibly know if the current flows into the battery or goes
to the other wire leading to the fusebox?


By measuring the voltage drop across those cables, stupid.

Unless there's some clever circuitry monitoring each
battery wire individually and subtracting the currents,


Yes there is, its called the computer.


So what happened with older cars before they did that?


The voltage across the battery changes as the battery is charged.


Wrong. Say the alternator can produce 14V at up to 50 amps. When the battery has been used to start the car and perhaps run some lights when the engine was off, it takes maybe 25A, and the voltage is 14V, regulated by the alternator's circuitry. When the battery becomes full, it takes only a fraction of an amp, but the voltage is still 14V. What needs to be measured is the current going into the battery, and that cannot be done by just measuring the current coming from the alternator, as that could also be going to lights, heaters, spark plugs, etc, etc.

the alternator can't tell the difference between a battery taking 12
amps,
and a battery taking 2 amps plus lights taking 10 amps.

But the computer can. And knows if the lights are on too.

The second one requires switching to trickle charge, the first doesn't.