How to charge laptop battery directly?

Question

Iron

The charge controller on the laptop failed. As a result, the laptop works while there is a charge on the battery, but it does not see the charge. the battery is not charging.

backstory

Подобная проблема у меня уже была, контроллер заряда очень трудно найти, да и ремонт в сервисном центре составил 40% от стоимости ноутбука. Сам по себе ноутбук в остационаренном состоянии: экран, тачпад. клавиатура вышли из строя. подключил внешний монитор, мыш и клаву.

In connection with the background, the idea arose not to repair the laptop, but to charge the battery directly. If it lasts a couple of months, then good.
Battery c21-x402ca. 7.4v 5136mAh, 38Wh.
I did not find the pinout / Datasheet.
The colors are:
3 black. yellow, white, 3 red.
I have a universal laptop charger. It can be switched to 12V. If you take a voltage converter from 12 to 7.5 and directly connect it to the battery, then:
1) Will the battery be charged?
2) If so, is it possible to turn on the laptop at this time?
3) If the battery does not charge, will the laptop start up with this scheme?

Answer 1

For starters, your battery is not a typical 18650, but full-fledged flat Li-ion batteries, which completely changes the rules of the game (repair).
Your controller is blocked by hardware when overdischarging (this is normal), you can only look for the controller chip and resolder.
1. No, fuck. Or just won't charge.
2. It is possible, because it has already banged.
3. Usually, a laptop can work without a connected battery from the mains supply.
Lithium should be charged by the controller, manual charging with a fixed voltage and current is harmful and dangerous.
If you consider yourself a person capable of repairing (which can be extremely dangerous):
1. Open the battery case without damaging the batteries themselves.
Presumably there are 2 or 4 of them.
I do not even want to write further for security reasons. PS A new battery costs about 2k.

Answer 2

The laptop itself is in a stationary state: screen, touchpad. the keyboard is out of order. Connected an external monitor, mouse and keyboard.

In such a situation, I would think very well whether it is worth investing money and effort in its repair. And most likely would have come to a decision - it's not worth it.

I did not find the pinout / Datasheet. The colors are: 3 black. yellow, white, 3 red.

Yellow and white - the data transmission line between the battery controller and the computer (the controller signals the degree of charge, temperature, etc.), it affects charging. Black and red are, of course, minus and plus, and I believe that not only the load current is removed through them, but also the charging current is supplied. If there was confidence that the controller is operational, charging through these conclusions could be checked experimentally. But you, as I understand it, do not have such confidence. The battery controller performs a bunch of functions (protection against overcharging, overdischarging, overcurrent during charging and discharging, overheating, and balancing), and in this case the last one is the most critical for you - balancing, i.e. making sure that both cells of the battery are in the same condition.

I have a universal laptop charger. It can be switched to 12V. If you take a voltage converter from 12 to 7.5 and directly connect it to the battery, then: 1) Will the battery be charged?

You can’t do this, even if it seems that everything is OK. In fact, you propose to operate a lithium battery without a controller - and then who will deal with the above protections? Lithium is not an acid battery, which in case of trouble will only boil away, lithium explodes or burns. Therefore, a workable controller is simply inevitable.
Now about how to solve the problem. It is best to make a tap from the middle of the battery (i.e., the points of serial connection of its elements) and connect an external controller to these three outputs. It is easy to find it by the keywords "BMS 2S", there are many of them on Ali. It must have a charge input - there and connect a charging current source with a voltage of 2 ... 3 volts more than the maximum battery voltage - in this case it is 9 ... 10 volts. Next, carry out a test charge-discharge under your own supervision, controlling the voltage of the cells with a multimeter (the BMS should not allow the voltage of the cells to rise more than 4.15 volts, and decrease below 3.0 volts, and the voltages of both cells should remain the same), and after that, if everything is OK, you can and without supervision.

Answer 3

the lithium battery will be charged according to the CC / CV - Constant Current + Constant Voltage system.
those. the charge current is limited so as not to overheat the battery. and limit the voltage on the battery, because exceeding this voltage kills the chemistry inside the battery, plus the battery may ignite.
the maximum charging current is usually taken 0.1 ... 0.5 C (and up to 1.0 C for fast charging, where C is the battery capacity)
0.5 * 5136 \u003d ~ 2500 mA. those. you can safely charge with a current of up to 2.5 A. but choose a smaller one - it will be calmer.
charging end voltage - 4.2 V per cell. you have two of them, so you need to charge up to 8.4 volts. exceeding even 0.2 V can seriously ruin the battery. therefore, if you are not sure about the quality of the charger, take a voltage of 8.2 V.
1) I described the charging conditions above.
2) yes you can, the lithium battery does not have a "memory effect", so it can be discharged / charged as you like.
in this case, if the current output by charging is higher than the current consumption of the note, then the battery will be charged. if on the contrary, then discharge.
3) power the laptop through a standard power connector. charge the battery separately.
in principle, you can take a power supply with an adjustable output voltage of 5-10 watts and charge the battery from it. the main thing is that the voltage is kept exactly and there is a current limit.