XPost: uk.rec.driving, alt.home.repair, uk.d-i-y   
   From: CFKinsey@military.org.jp   
      
   On Sat, 22 Jun 2019 17:03:08 +0100, TMS320  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?   
   >   
   > It doesn't.   
      
   Mine does, if I start my car when the battery is say 80% full, the voltage   
   will be 14.4V.  After a while, something causes that voltage to drop to 13.8,   
   because something knows the battery is full and should no longer be charged at   
   a high rate.   
      
   >> 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?   
   >   
   > Ohm's law.   
      
   Explain how an alternator or charger can use ohm's law to distinguish between:   
   1) A car battery which is full, with a load of 10 amps connected to it, like   
   two headlights.   
   2) A car battery with no load, which is not full yet and draws 10 amps for the   
   charge.   
      
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