XPost: uk.rec.driving, alt.home.repair, uk.d-i-y
From: rod.speed.aaa@gmail.com
"Xeno" wrote in message
news:gn84kjF24gkU1@mid.individual.net...
> 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.
>>
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