Why does a battery need 3 contacts and what happens to it when it is recharged?

Question

Electronics

Good evening, tell me please
Why does a battery on digital technology need 3 contacts, if it can be charged from two?
And what happens to the battery when it is charged to the maximum and left to charge further, plugged into the network? Does the charger have any safety mode after the battery is fully charged?
And the charging speed of the battery depends on the diameter of the wires in the charging transformer?
Their ratio is 230 on the primary and 6 on the secondary?

Answer 1

Why does a battery on digital technology need 3 contacts, if it can be charged from two?

The third pin is used to transfer data using the 1-Wire protocol (on batteries with 4 or more pins, for example, in laptops, the i2c protocol is used).
The battery has a built-in temperature sensor and a charge control controller that reports the percentage of charge and is able to turn off the battery in case of overdischarge or overcharge. There are also dumber batteries, where the third pin is wired to the thermistor and serves only to measure temperature.
Cooler functionality can also be assigned to the battery. In Sony cameras, the battery drove the backlight of the display, in the PSP, the battery controlled the service launch mode of the set-top box, in the latest revision they even put AES encryption and key exchange there. Yes, all this is on the third contact.
the lithium battery is charged according to the CC-CV (Constant Current - Constant Voltage) scheme. At the initial stage of charging, the charger ensures that the charging current does not go beyond the permissible limits (usually about 1C, that is, approximately equal to the battery capacity in mAh). As soon as the battery voltage approaches the maximum allowable (4.2 V for normal, sometimes 4.35 V for high-capacity batteries, 3.6 V for high-current LiFePO4), charging limits the current so that the voltage does not exceed this bar. That is, the charging itself ensures that overcharging never happens. It can be compared to filling a bucket first with a fast flow of water, as far as the hose allows, then decreasing the flow of water so that the splashing water does not overflow, at the end, gently add a drop to fill completely and not spill ....

And the charging speed of the battery depends on the diameter of the wires in the charging transformer?
Their ratio is 230 on the primary and 6 on the secondary?

In modern chargers there are pulse converters, no transformers. The charging speed is limited by 1) the maximum current that the charging can give out, 2) the maximum current that the phone can accept, 3) the wires through which the charging takes place. A regular USB can pass no more than 2 amps, then it will overheat and be unsafe. Instead of increasing the charging current, manufacturers have chosen to increase the voltage. Charging produces 12 volts, the phone inside converts to a lower voltage, with a large current. As a result, the wire does not heat up, and there are fewer losses. And the larger the battery capacity of the phone, the more current it can be charged, the more energy will accumulate at the initial stage of charging ....
Damn, I wrote a lot. Ask clarifying questions so as not to describe everything in a row.

Answer 2

... the speed of charging the battery depends on the diameter of the wires in the charging transformer?
Yes, full of cunts ... delight, of course, and not a question!
From the most literate nation in the Soviet Union - we have turned into this !!!
Although the question itself is of course very worthwhile and far from ambiguous.
A bunch of all sorts of destinations for the third leg of the battery are written here,
but all this is very vague and ambiguous.
For example, I liked the expression of the system programmer
... the device ensures that the charging current does not go beyond the permissible limits (usually on the order of 1C, that is, approximately equal to the battery capacity in mAh) ....
"It's like, I'm sorry to understand your mother .." Current is generally measured in amps.
and 1C is an accounting program!
Let's try on his advice to set the charge current for a battery with a capacity of 1200 mAh
So we connect plus to plus minus to minus and then WHAT ??
What current in amperes must be set in the circuit so that it is of the order of 1C ???
Oh well, it says "... that is, approximately equal to the battery capacity,
that is, 1200 of which he did NOT write, so let's take mA and get 1200mAh = 1.2 A
I hope even a cat understands that this is nonsense!
So let's do our own thing.
How everyone probably remembers - Pies - a pieman and boots - a shoemaker.But
the most interesting thing in this matter looks somewhat unexpected!
But nothing that you, having in front of you on the table
multimeter, load plug and two identical batteries,
you will not be able to clearly distinguish
the battery that was charged a couple of days ago
from the one you just took out of the phone, which itself turned off
due to battery discharge !!
Because they will both be charged! and the difference in current through the plug will be negligible!
And now let's remember how many such situations in life,
when very much can depend on the level of charge of the battery of a mobile phone?
And why should a battery that is still full of energy be sent for recharging?
I don’t know why it happens this way, but I saw it with my own eyes
and everyone can repeat my little experiment if they wish.