XPost: uk.rec.driving, alt.home.repair, uk.d-i-y   
   From: rod.speed.aaa@gmail.com   
      
   "Commander Kinsey"  wrote in message   
   news:op.z3q9fvpjwdg98l@desktop-ga2mpl8.lan...   
   > On Fri, 21 Jun 2019 22:57:44 +0100, Max Demian    
   > wrote:   
   >   
   >> On 21/06/2019 21:19, Commander Kinsey wrote:   
   >>> How does a lead acid battery charger (or car alternator) know when to   
   >>> switch to trickle charge?  I can understand it noticing a drop in   
   >>> charging current if the battery is on its own, but what if a random   
   >>> changing load is connected, as there is in a running car?   
   >>   
   >> The voltage perhaps.   
      
   > Why would the voltage change?   
      
   That's the way batterys work, the battery voltage does change as its   
   charged.   
      
   > That's determined by the alternator or charger.   
      
   Nope.   
      
   > Let's say the charger/alternator gives out 14.4V initially, to charge the   
   > battery quickly.  It'll just sit at 14.4V forever, providing the charger   
   > can give out enough current to charge the slightly flat battery and power   
   > any connected loads.   
      
   Its more complicated than that with the current going to the battery and the   
   battery is charged.   
      
   > If the battery had no loads connected, it would take a lot less current   
   > when it became full, but the voltage would stay the same.   
      
   No it doesn't even with a very crude battery charger.   
      
   > If the charger monitored the current it was providing, how does it know if   
   > the battery is still charging at 10 amps, or if the battery is full and   
   > there's a 10 amp load?   
      
   By checking the current actually being delivered to the battery.   
      
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