XPost: uk.rec.driving, alt.home.repair, uk.d-i-y
From: CFKinsey@military.org.jp
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.
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
>
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