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