Can I Safely Charge a Car Battery at Home with 30A? Comparing to 40A Alternator

Hello. For some time I have been wondering how it is that a typical battery charger has 6A, while the alternator in a car is 40A +.
So, could I safely charge the battery at home with 30A?

The alternator does not charge the battery with 30A.
Typical charging current is 1/10 of the capacity.

The alternator is over 40A, so how can it charge a 1/10 capacity battery?

Stock is needed because you have a few other items in your car that need electricity. The battery charging current is limited by the charging voltage.

beatom wrote:

The alternator does not charge the battery with 30A.

It charges with time and with higher current, depending on the degree of discharge of the battery, which is of course harmful to it.

In the old design of alternator regulators, charging the battery was indeed detrimental to the battery. In today's solutions / the on-board computer regulates the charging current / it is more delicate.

There is a method of charging the battery that the producers sometimes mention, namely the so-called quick charging with 0.8 C current. It is allowed only in emergency situations, as it strongly damages the battery. Then, there is a strong heating and gassing of the electrolyte, the active mass falls out of the plates (the cell may short-circuit) and the plates themselves bend. So even if the battery does not die, it will definitely shorten his life significantly. Why am I mentioning this? Because a similar situation is when we torture a weak battery with a few minutes of starting, finally the car fires and the altek starts loading. The voltage is stiff 14.4V and the battery draws as much current as the altek gives it (and it can even give it 50A depending on the consumption from other receivers). So you can charge the battery with high currents, but still it shouldn't be done, because the benefits are smaller than the losses. But if there is no breakdown in the car, and we use it properly, such situations practically do not occur ...

First of all, you need to start with the fact that the current value given on the alternator determines its efficiency, it is not information how much current flows from the alternator.
This is only information that up to the maximum load of X amps, the alternator will maintain the rated voltage of 14.4V.
How many amps will flow from the alternator depends on how many amps are needed by the devices connected to it.
There is no such thing as a typical battery charging current in a normal automotive installation.
Most often it is a simple cable connection, because nothing else is needed there.
The alternator gives a voltage of 14.4V, the rated voltage of the battery is 12.6-12.8V. This potential difference causes that electricity flows to the battery, i.e. it is charged.
The charging current of the battery depends on the potential difference of the battery-generator, so the lower the voltage of the battery, the greater the potential difference and the greater the charging current.
The value of the charging current is also influenced by the battery capacity because its Rw depends on it, so the higher the battery, the greater the charging current with the same battery-alternator potential difference.

So there is no magic or finesse here (in a simple "classic" solution, of course).
It is a simple circuit that balances naturally and the charging current is typically a few amps, of course with the "normal" battery condition.

Zbigniew 400, I am asking out of curiosity ... how old are you writing about?
Because I remember that there were no miracles in the Polonaise, and the battery lasted the same as in modern computers on wheels

kolibercio wrote:

Hello. For some time I have been wondering how it is that a typical battery charger has 6A, while the alternator in a car is 40A +.
So, could I safely charge the battery at home with 30A?

The matter is simple and there is no contradiction here. An alternator with a rated current of 40 A can charge the battery with this current as long as the internal resistance of the battery allows it, and let me remind you that the resistance of the car battery is 5 mOhm. In fact, with a deeply discharged battery, the current can reach tens of amps, but only for a short while after starting the engine. As the voltage at the battery terminals increases, the current will decrease. In fact, the battery current is also limited by the resistance of the windings. As it is commonly known, alternators only have a voltage regulator, there is no separate current regulator (as in the old DC generators). It is not needed for the reasons mentioned above. So there is no harm to the battery in the car. The same can be designed a charger for a battery with a maximum capacity, e.g. 30 A, but with a voltage limitation, e.g. up to 14V. This will cause the connected, discharged battery to consume a large current for a short time, which quite quickly (as the voltage on the battery increases) will drop practically down to mA with a fully charged battery.

Greetings!

Old solutions are the Polonez / internal regulator that sets the voltage of the alternator /. In newer solutions, the computer controls the voltage depending on the condition of the battery, faster recharging / starts, winter / or lowering charging / temperature /. Alaska and Africa different voltages in the car's installation.

Zbigniew 400 wrote:

Old solutions are the Polonez / internal regulator that sets the voltage of the alternator /. In newer solutions, the computer controls the voltage depending on the state of the battery, faster recharging / starts, winter / or lower charging / temperature /

To my knowledge, this old solution is used to this day in 99% of cars on our roads. Controlling the alternator with a computer is maybe in some expensive Lexus or other hybrid inventions Although, to be honest, I do not know why anyone would produce something like this for an ordinary car. All you need is an alternator and a voltage regulator.

Zbigniew 400 wrote:

Alaska and Africa have different voltages in the car installation.

There is just another version of the regulator. For climatic reasons in Africa ~ 13.5V and in Alaska ~ 14.5V.

Quote:

There is just another version of the regulator. For climatic reasons in Africa ~ 13.5V and in Alaska ~ 14.5V.

This is the first time I hear about it ....

^ToM^ wrote:

Zbigniew 400 wrote:

Old solutions are the Polonez / internal regulator that sets the voltage of the alternator /. In newer solutions, the computer controls the voltage depending on the state of the battery, faster recharging / starts, winter / or lower charging / temperature /

To my knowledge, this old solution is used to this day in 99% of cars on our roads. Controlling the alternator with a computer is maybe in some expensive Lexus or other hybrid inventions Although, to be honest, I do not know why anyone would produce something like this for an ordinary car. All you need is an alternator and a voltage regulator.

You are indeed right, normally all you need is an ordinary voltage regulator. But not nowadays, when you have to complicate everything as much as possible (so that everything should break) and connect to the computer. Today, new cars (and not those of the top shelf) use intelligent charging regulators controlled by the ECU. It is supposed to bring many benefits, extending the life of the batteries or reducing fuel consumption. But somehow I doubt these benefits ...

http://truckfocus.pl/nowosci/6181/wazna-rzecz-regulatory-napiecia-w-alternatorach

The fact that the rectifier has 6A and the alternator 50A, it only means that you can safely draw so much electricity from these devices for some time. And you get a lot more out of it, Ohm's law bows. And as for charging, I have already written here.
https://www.elektroda.pl/rtvforum/topic100799.html#8930747
I will only add that with this method of charging, damaged or sulphated batteries are heated. Serviceable and worn, but not sulphated. In addition, they do not gas and the entire charging process is fast.
And so from myself I will add that after almost 3 years I finished 500 cycles of charging two 7.2Ah gel batteries. Charged quickly and slowly (one fast and the other slow with 1/10 current). Same result, both got used up at the same time. In fact, after 350-380 cycles, the loss of capacity was already visible. And after these 500, they only had 2Ah with a capacity of them, so I skipped the next cycles.

Falco76 wrote:

Quote:

There is just another version of the regulator. For climatic reasons in Africa ~ 13.5V and in Alaska ~ 14.5V.

This is the first time I hear about it ....

You see, it's worth reading an electrode - you can always learn something new. I have found out about it more than once. And by the way, I refer you to books on automotive electrical engineering where this problem is explained in more detail. The problem essentially concerns the charging voltage as a function of the ambient temperature. As it is known, in tropical countries the average temperature is different than in Europe or Alaska, hence the car for export to tropical countries receives different equipment (also a voltage regulator) than that for sale, for example, in Europe. There is nothing revealing here.

Best wishes!

In Kamazy there was a screw on the alternator marked winter / summer. In hot climates, the electrolyte in batteries has a lower concentration.

Of course it's worth reading the electrode. Man learns all his life.