XPost: uk.rec.driving, alt.home.repair, uk.d-i-y   
   From: xenolith@optusnet.com.au   
      
   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.   
      
      
   >   
   > 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   
   >>   
      
      
   --   
      
   Xeno   
      
      
   Nothing astonishes Noddy so much as common sense and plain dealing.   
          (with apologies to Ralph Waldo Emerson)   
      
   --- SoupGate-Win32 v1.05   
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