XPost: uk.rec.driving, alt.home.repair, uk.d-i-y   
   From: rod.speed.aaa@gmail.com   
      
   "Xeno"  wrote in message   
   news:gn6a5eFkg1fU1@mid.individual.net...   
   > On 22/6/19 9:57 am, 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.   
   >>   
   >>> The battery then chooses how much current is drawn.   
   >>   
   >> And that current changes depending on the how charged the battery is.   
   >>   
   >>>>> 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.   
   >>   
   >>> 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.   
      
   > Correction   
      
   Nope.   
      
   > the *battery* is the *load*.   
      
   Not when the battery is fully charges and is being charged   
   with a bench supply that is delivering 4A to the battery.   
      
   > In the process of being charged it is using electric current. That makes   
   > it the load.   
      
   See above.   
      
   > Even when it is fully charged it will still take a trickle charge   
      
   4A isnt a trickle charge.   
      
   > so it is still a load even when fully charged.   
      
   Not when its still taking 4A,   
      
   >>>>> 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.   
   >>   
   >>> I guess that may be true, if the car's computer has two ammeters   
   >>   
   >> It has more than one wire to the positive terminal of the battery.   
   >> So it can see what current is going to the rest of the car.   
   >>   
   >>> and subtracts one from the other.   But AFAIK, the alternator regulator   
   >>> only works by it's own current sensor.  And that current could be going   
   >>> into the battery, or past it to the loads.   
   >>   
   >> Not when there is more than one wire going to the   
   >> positive terminal of the battery, and there always is.   
      
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