XPost: uk.rec.driving, alt.home.repair, uk.d-i-y
From: rod.speed.aaa@gmail.com
"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,
> If the battery is *taking* 4 amps, then it *is definitely the load*.
But it wont be taking 4A WHEN THE BATTERY IS OUT OF THE
CAR WITH A BENCH SUPPLY. Because the battery voltage will
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