"Xeno" wrote in message
...
On 24/6/19 7:42 pm, trader_4 wrote:
On Sunday, June 23, 2019 at 7:11:16 PM UTC-4, Clare Snyder wrote:
On Fri, 21 Jun 2019 13:48:56 -0700, % wrote:

On 2019-06-21 1:19 p.m., 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 catalytic converter tells it
I can tell you how an alternator does it, chargerscan do it
differently. AN alternator doesn't "switch to trickle charge". AN
alternator limits the output voltage. A battery will only accept a
certain amount of charge at any voltage. At 14.6 volts it basically
stops taking a charge. The regulator is set to limit the voltage to a
specified voltage - 13.8 or 14.2, or something similar. An alternator
is intrinsically current limitted so will not provide more than the
rated current, If the battery open circuit voltage is below 12 volts
it will tale pretty close to whatever the alternator can put out, as
the open circuit voltage increases, the amount of charge it will
accept decreases, untill at 14.6 volts or whatever is designed as full
charge, it will no longer accept ANY charge. As the load changes, the
alternator provides more or less current as required to maintain the
fully charged voltage.

Clear as mud???

Bingo! Thank you. Exactly what I and Xeno have been saying and now
we have a mechanic confirming it.

We had a mechanic confirming it when I was saying it since I am also a
mechanic. Served an apprenticeship and been in the trade since the 60s.
;-)

Problem is that you are so stupid that you can't even manage
to work out that there is no open circuit voltage in a car with
the alternator charging the battery, so something else has to
be used to work out when the battery is charged, and that can
only be the current its taking and that is easy to measure when
there is more than one wire at the battery positive terminal.