XPost: uk.rec.driving, alt.home.repair, uk.d-i-y
From: xenolith@optusnet.com.au
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 - the *battery* is the *load*. In the process of being
charged it is using electric current. That makes it the load. Even when
it is fully charged it will still take a trickle charge so it is still a
load even when fully charged.
>
>>>> 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.
--
Xeno
Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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