XPost: uk.rec.driving, alt.home.repair, uk.d-i-y   
   From: xenolith@optusnet.com.au   
      
   On 23/6/19 1:30 am, Rod Speed wrote:   
   >   
   >   
   > "Xeno"  wrote in message   
   > news:gn6eudFlh2sU1@mid.individual.net...   
   >> On 22/6/19 7:58 pm, Rod Speed wrote:   
   >>>   
   >>>   
   >>> "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 charged and is being charged   
   >>> with a bench supply that is delivering 4A to the battery.   
   >>   
   >> Take the case of an alternator charging a battery at ~4 amps.   
   >   
   > That isnt what was being discussed there. What was being discussed   
   > there was charging the battery out of the car with a bench supply.   
   >   
   >> The battery is the load and it also provides, as part of that   
   >> function, the  reference *voltage* that the alternator *must have* in   
   >> order to control  the output.   
   >   
   > None of that is relevant to what was being discussed there,   
   > charging the battery out of the car with a bench supply.   
   >   
   >>>> In the process of being charged it is using electric current. That   
   >>>> makes it the load.   
   >   
   >>> See above.   
   >   
   >> What happens to the charger when you disconnect the power with the   
   >> battery connected?   
   >   
   > With a BENCH SUPPLY, it continues to provide the   
   > same voltage as it did with the battery connected.   
   >   
   >> It should, if designed correctly, shut down since it no longer sees a   
   >> load. Otherwise it may destroy itself.   
   >   
   > That is just plain wrong with a BENCH SUPPLY.   
   > None of those destroy themselves with no load.   
   >   
   >>>> Even when it is fully charged it will still take a trickle charge   
   >   
   >>> 4A isnt a trickle charge.   
   >   
   >> That depends entirely on the amp hour rating of the battery.   
   >   
   > We're discussing a normal car battery in a steaming turd with   
   > wheels frog car.   
   >   
   >> Also, my bench charger   
   >   
   > We arent discussing a bench charger, we are discussing a bench SUPPLY.   
   >   
   >> will start off at 4 amps, its maximum capacity. As the battery becomes   
   >> charged, that current will drop down to *1 amp* and, from that point,   
   >> it will maintain a *trickle charge*.   
   >   
   > So that is nothing like the situation being discussed   
   > with a BENCH SUPPLY which is still delivering 4A to   
   > a battery that has been removed from the car.   
   >   
   >> From Wikipedia;   
   >>     For lead-acid batteries under no load float charging (such as   
   >>     in SLI batteries), trickle charging happens naturally at the   
   >>     end-of-charge, when the lead-acid battery internal resistance   
   >>     to the charging current increases enough to reduce additional   
   >>     charging current to a trickle, hence the name. In such cases,   
   >>     the trickle charging equals the energy expended by the   
   >>     lead-acid battery splitting the water in the electrolyte into   
   >>     hydrogen and oxygen gases   
   >   
   > Irrelevant to what is being discussed, 4A isnt a trickle charge.   
   >   
   >> The car alternator regulator is no different.   
   >   
   > We arent discussing that there.   
   >   
   >> It sees the battery as a load, determines the voltage reference and   
   >> pumps up its output. When the regulator sees the battery voltage at   
   >> the peak setpoint, it too will drop the current to a trickle. If you   
   >> add a load, say by turning headlights on, that is in *parallel* to the   
   >> battery and it will drop the system voltage down a tad. The regulator   
   >> will see that and pump up the output current appropriately. The   
   >> current will apportion itself to the *two* loads as appropriate to   
   >> their individual internal resistances.   
   >   
   > All irrelevant to charging a battery out of the car with a BENCH SUPPLY.   
   >   
   >> Here, educate yourself;   
   >> https://www.swtc.edu/ag_power/electrical/lecture/parallel_circuits.htm   
   >   
   > I knew all that before you were even born, thanks.   
   >   
   >>>> so it is still a load even when fully charged.   
   >   
   >>> Not when its still taking 4A,   
   >   
      
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