XPost: uk.rec.driving, alt.home.repair, uk.d-i-y   
   From: dr6092@gmail.com   
      
   On 22/06/2019 22:58, Commander Kinsey wrote:   
   > 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:   
      
   To determine current, measure the voltage across a series resistor, duh.   
      
   > 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.   
      
   Two resistors?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)