XPost: uk.rec.driving, alt.home.repair, uk.d-i-y   
   From: CFKinsey@military.org.jp   
      
   On Fri, 21 Jun 2019 23:39:34 +0100, Rod Speed  wrote:   
      
   >   
   >   
   > "Commander Kinsey"  wrote in message   
   > news:op.z3q6mue3wdg98l@desktop-ga2mpl8.lan...   
   >> On Fri, 21 Jun 2019 21:54:38 +0100, 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.   
   >>>   
   >>>> 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?   
   >>>   
   >>> You just look at the current going to the battery. The variably   
   >>> loads like with lights isnt supplied by the battery when the   
   >>> engine is running, its supplied by the alternator.   
   >   
   >> But how can the regulator on the alternator possibly know the current it's   
   >> passing to the battery is going into the battery and not going straight   
   >> across to the lights?   
   >   
   > The computer knows whats going to the battery and you can see that with an   
   > ODB2 dongle.   
      
   My dongle only lists faults.   
      
   >> If you look at the battery in your car, there are two or three thick wires   
   >> coming off each terminal.  One will go to the alternator, another to the   
   >> fusebox for all the lights etc.   
   >   
   > And it's the voltage across the one going from the alternator to the battery   
   > that allows the computer to know how much current is going to the battery.   
      
   Bullshit.  How could it possibly know if the current flows into the battery or   
   goes to the other wire leading to the fusebox?   
      
   >> Unless there's some clever circuitry monitoring each battery wire   
   >> individually and subtracting the currents,   
   >   
   > Yes there is, its called the computer.   
      
   So what happened with older cars before they did that?   
      
   >> the alternator can't tell the difference between a battery taking 12 amps,   
   >> and a battery taking 2 amps plus lights taking 10 amps.   
   >   
   > But the computer can. And knows if the lights are on too.   
   >   
   >> The second one requires switching to trickle charge, the first doesn't.   
      
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