XPost: uk.rec.driving, alt.home.repair, uk.d-i-y   
   From: CFKinsey@military.org.jp   
      
   On Sat, 22 Jun 2019 00:57:57 +0100, Rod Speed  wrote:   
      
   >   
   >   
   > "Commander Kinsey"  wrote in message   
   > news:op.z3rc17q7wdg98l@desktop-ga2mpl8.lan...   
   >> On Fri, 21 Jun 2019 23:57:52 +0100, Rod Speed    
   >> wrote:   
   >>   
   >>>   
   >>>   
   >>> "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.   
   >>   
   >> Yip.   
   >   
   > Nope.   
   >   
   >> I can put any voltage I like across a battery's terminals.   
   >   
   > Nope.   
      
   I can if the charger / power supply is powerful enough.   
      
   >> The battery then chooses how much current is drawn.   
   >   
   > And that current changes depending on the how charged the battery is.   
      
   Correct, it's the current it checks.   
      
   >>>> 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.   
   >   
   >> For example, I'm currently keeping my car's battery topped up with a bench   
   >> supply overnight.  It's set to 13.8V, with a current limiter only to   
   >> prevent overloading the supply.   
   >   
   > It actually specify the current being supplied.   
      
   No, it LIMITS the current.  I set 13.8V, 2.5A.  It will back off if either is   
   exceeded.   
      
   >> The voltage stays at 13.8V all the time, sometimes 100mA is drawn,   
   >> sometimes up to 4A.  The only way I or the supply can tell the battery is   
   >> full, is by the current dropping to 100mA.  But it's actually always full,   
   >> as when 4A is drawn, that's going to a load.   
   >   
   > What load ?  There no load with a battery being charged with a bench supply.   
      
   The faulty frog car with the dodgy alarm.   
      
   --- SoupGate-Win32 v1.05   
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