XPost: uk.rec.driving, alt.home.repair, uk.d-i-y   
   From: CFKinsey@military.org.jp   
      
   On Sat, 22 Jun 2019 00:26:13 +0100, Rod Speed  wrote:   
      
   >   
   >   
   > "Commander Kinsey"  wrote in message   
   > news:op.z3rauixewdg98l@desktop-ga2mpl8.lan...   
   >> 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.   
   >   
   > Because it's a steaming turd with wheels frog car.   
      
   Which should adhere to the fucking OBD standards according to the frog's own   
   EU regs!!   
      
   And a very basic OBD reader I bought to determine why a warning light was on.   
      
   > Most show all sorts of things.   
   >   
   >>>> 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.   
   >   
   > We'll see...   
   >   
   >> How could it possibly know if the current flows into the battery or goes   
   >> to the other wire leading to the fusebox?   
   >   
   > By measuring the voltage drop across those cables, stupid.   
   >   
   >>>> 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 voltage across the battery changes as the battery is charged.   
      
   Wrong.  Say the alternator can produce 14V at up to 50 amps.  When the battery   
   has been used to start the car and perhaps run some lights when the engine was   
   off, it takes maybe 25A, and the voltage is 14V, regulated by the alternator's   
   circuitry.  When    
   the battery becomes full, it takes only a fraction of an amp, but the voltage   
   is still 14V.  What needs to be measured is the current going into the   
   battery, and that cannot be done by just measuring the current coming from the   
   alternator, as that could    
   also be going to lights, heaters, spark plugs, etc, etc.   
      
   >>>> 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.   
      
   --- SoupGate-Win32 v1.05   
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