XPost: alt.home.repair, uk.d-i-y, uk.rec.driving   
   From: CFKinsey@military.org.jp   
      
   On Fri, 21 Jun 2019 22:18:56 +0100, trader_4  wrote:   
      
   > On Friday, June 21, 2019 at 4:54:51 PM UTC-4, Rod Speed wrote:   
   >> Commander Kinsey  wrote   
   >>   
   >> > How does a lead acid battery charger (or car alternator) know when to   
   >> > switch to trickle charge?   
   >>   
   >> From the current the battery takes.   
   >   
   > Except that the alternator doesn't know how much current is going   
   > into the battery and how much is being used to power the car.   
   > At least not in any car I've had.  The alternator is tied directly   
   > to the battery and that common point supplies the car.  The alternator   
   > can't switch to trickle charge either.  Every one I've seen, with   
   > the car running normally, the voltage at the alternator/battery is   
   > about 13.5 - 14V   
      
   I used to think the same, until someone in one of these newsgroups (on another   
   topic about 6 months ago) said it drops the voltage or it would wear out the   
   battery on long journeys.  I tested my own car, by leaving the lights on for a   
   bit, then starting    
   it.  The voltage was about 14.4.  It dropped to 13.8 after the battery was   
   filled up.  The regulator must have detected the battery was full somehow and   
   lowered the charging voltage.   
      
   Mind you after some googling, apparently a lead acid is happy being charged   
   from 13.8 to 14.5 continuously.  Although when I used to leave my car on a   
   charger (an old Bradex car battery charger) at 14.5, it fucked the battery   
   after a few months.  Maybe    
   14.5 is only ok in a car alternator circuit, which isn't usually running 24   
   hours a day.  I think I'll always make sure it's 13.8 if it's on charge all   
   the time - my car tends to randomly lose battery power overnight (to the alarm   
   I believe).  I was just    
   wondering if I bought an intelligent car battery charger, whether it would   
   ever switch down to trickle if the alarm was sucking juice, as such a charger   
   may not expect any load.  I currently have it connected to a bench supply at   
   13.8.   
      
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