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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 Thu, 11 Jul 2019 14:47:33 +0100, Xeno wrote:

On 11/7/19 5:11 am, Commander Kinsey wrote:
Well I see the full voltage charging a flat battery at idle. Obviously
they could be designed to be capable of this and it would be very useful
to charge the battery quickly when doing stop start town driving, or
driving at minimum revs in top gear in a town.

You may see a high voltage but you will not see a high current at idle.
The alternator is not *capable* of high current at idle.


A flat battery at a high voltage means there's a high current.

And will you please stop mixing up top and bottom posting. I top posted because I was replying to a blind user who had done the same.


On Sun, 23 Jun 2019 07:07:14 +0100, Xeno wrote:

On 23/6/19 5:47 am, Commander Kinsey wrote:
Modern car alternators seem to be able to give out a huge amount of
current at engine idle speed. I'm sure my friend got his to give out
pretty much the full 80 amps without revving the engine. He was
powering a small disco on a campsite :-)

No way to get a full 80 amps out of an alternator *at idle*.

On Sat, 22 Jun 2019 11:00:34 +0100, Brian Gaff
wrote:

Yes indeed, the nominal output of an alternator can be as high as 15
volts,
but even a fully charged car battery is only 13.8v as far as I know and
these days, I'm sure the direction of current flow and voltages are
monitored very well by the computers. In the old days it was a bit of a
black art just relying on the ability of the alternator or dynamo in
the old
bangers.
Normally the output will change due to engine speed, but in
alternators
there is a voltage regulator inbuilt to keep the thing pretty
nominal and
of course the thing that then suffers is the charging rate, ie its
going to
be be slower when its not running very fast. I think if a battery dips
below
about 11v outside of starter transients, you have to charge it or get
a new
one. This very accurate sensing these days can often mask a battery
on its
last legs though, as people tend to ignore warnings if the car still
works,
then they leave it a couple of days and it won't start!

Brian