Lenovo SL510 does not charge the battery - Charge Circuit

[wilder1626]

Hi all,
I have a Lenovo SL510 motherboard that won't charge the battery. Windows, bios update, battery, power supply are 100% fine. So I decided to look at the motherboard and see if something was wrong with the power circuit. I saw that the connector solder was yellow. So I redid the soldering and it's now fine, but still does not charge the battery.

My power supply is Output: 20V 4.5A

I found the diagram about the charge circuit:

The fuse test i did on my motherboard was giving me 4.1 volts.

I also saw that PWR1, PWR2. are giving me 4.0 volts while I2C_CLK, I2C_DATA and TEMP give 3.36 Volts.

I'm a beginner at understanding a diagram, but if I'm not mistaken, I don't seem to have enough voltage to charge my battery. Is this possible?

Do you have any advice for me?

Thanks for your help.

 

[rjenkinsgb]

There should be some power MOSFETs connected to the battery circuit - one to control power in for charging, from the external power connector, and another one (or more) for the battery out to the rest of the machine.

That's likely the area you need to be looking at.

The device at the very left of the photo, next to the 10A fuse, could well be one of the power control MOSFETs?

 

[technofreak]

Laptop motherboards will have battery management IC, you need check data sheet of (IC, Transistor) components of battery charger circuit.

Came across this..

Lenovo Schematic image

 

[wilder1626]

Thanks rjenkinsgb and technofreak
I will have a look at the MOSFETs for sure and check the schematic. Will get back to you right after.

I also had that full diagram.

 

[rjenkinsgb]

I will have a look at the MOSFETs for sure and check the schematic.

First thing to check is the input fuse, PF5 - top left of the schematic?

Those can sometimes be blown by repeatedly connecting the charger to the laptop, with the charger already connected to AC power.

The external power on/off FET look to be PQ31, at the upper right.

Does the machine run from external power? If not, it's almost certainly something along the top line of the circuit, from the DC-IN connector at the left through to PQ31 and the V-IN point at the right.

If it does work from external power but does not charge the battery, then it's something deeper in the guts of the charge controller..

 

[wilder1626]

If it does work from external power but does not charge the battery, then it's something deeper in the guts of the charge controller..

Yes, it works with an external power. Only the battery does not charge.

Okay, I'll start validating PF5.

 

[rjenkinsgb]

If it works from external power, the top section of the circuit is OK, including that fuse.

If the battery voltage has got too low, it may mean a cell has failed so the battery charge is disabled by the controller. Lithium batteries often lock out if they get down to near 3V per cell or on any one cell.

Where were you getting the 4.1V, left or right of PF1? If that was from the battery, it's waaay to low. Is it the same both sides of the fuse?
And, have you tried a different battery?

 

[wilder1626]

Where were you getting the 4.1V, left or right of PF1? If that was from the battery, it's waaay to low. Is it the same both sides of the fuse?
And, have you tried a different battery?

There was 4.1V on both sides, and it wasn't coming from the battery. But I can tell you that the battery had not been used for over a year, whereas it was brand new and had only been used for about a week. Nor have I tested it with any other battery.

So I'm wondering if the battery charge is disabled by the controller.

 

[rjenkinsgb]

What voltage does the battery itself give?

 

[wilder1626]

Sorry for the delay. I will have to test it outside the laptop. Will validate, and will let you know.

 

[wilder1626]

Just testing the battery, not connected to the laptop, I have 1 mV on the multimeter.

But the last time I used it, in March 2022, it was fully charged and the battery was brand new. That's where I'm at for now.

 

[wilder1626]

I was just able to give it a tiny charge without the laptop. I'm now at 8.47 v. Will continue later.

 

[wilder1626]

New update.

I started the laptop with the battery on it. It now charges the battery correctly. So maybe it was a combination of 2 things so far:

No1: the connector solder was yellow. I've corrected that.

No2: Since the battery had 0v, even though it was new from last year, but not used since, by giving it a small charge outside the laptop with the power supply, it now seems to work, or at least, the computer recognizes it.

I'll let it charge for 6 hours and do some more tests tomorrow.

Thanks again for all the guidance.

 

[wilder1626]

New update. Laptop now says Battery 100%

 

[rjenkinsgb]

Great stuff.
To get the best out of it, leave it on charge after it's showing 100% for several hours over the next three charges, and run the machine to the point the battery is dead each time.

The extra charge is to give the cell balance circuit in the battery pack time to get the cells back "in sync" and all working at the same voltage, and the total discharge helps calibrate the battery capacity measuring system.


Don't then leave it on charge after full, disconnect power and run from the battery when full, or better still when it reaches around 80%, and put back on charge when it's down to 20%.

Just give it a full charge - full discharge every few months.

Keeping the charge level nearer 50% and avoiding full/empty can allow the battery to last a good few years, twice as long as fully charging and fully discharging every time, and 10 - 20 times longer than if it's permanently connected to power.

 

[wilder1626]

New update, it seems like my Lenovo 45N1001 battery is typically designed to have a nominal 10.8 V or 11.1 V.

Now that it's 100% charged using the laptop, using a multimeter, i see that I'm getting 11.98 - 12 volts on it.

So it seams like it's higher than the expected nominal voltage of the 45N1001 battery.
Could there be a small voltage discrepancy acceptable range without causing any problems? That seems a bit high to me.

 

[Nigel Goodwin]

New update, it seems like my Lenovo 45N1001 battery is typically designed to have a nominal 10.8 V or 11.1 V.

Now that it's 100% charged using the laptop, using a multimeter, i see that I'm getting 11.98 - 12 volts on it.

So it seams like it's higher than the expected nominal voltage of the 45N1001 battery.
Could there be a small voltage discrepancy acceptable range without causing any problems? That seems a bit high to me.

It depends entirely on what you consider the 'nominal' voltage of the battery - personally I consider the nominal voltage of a Li-Ion cell to be 4.2V (it's fully charged voltage) - so three in series would be 12.6V. So your charging system is probably restricting it from 'full' charge due to fast charging, for this reason I generally charge fairly slowly, so as to maximise the amount of charge, and extend the life time of the battery. Fast charging reduces long term battery life, and also doesn't provide full charge to the battery.

It's all swings and roundabouts, optimising charging time against battery life - plus the fear of potential fires has resulted in more conservative charging schemes.

 

[wilder1626]

Thanks for the information.
One thing is for sure, the battery is really not hot. It's normal temp to me. So I'm assuming it's all normal.

The "nominal" battery voltage value was given on a website I consulted. But I also understand your calculation of the 3 series of the 4.2V pack which equals 12.6V.

 

[Nigel Goodwin]

Thanks for the information.
One thing is for sure, the battery is really not hot. It's normal temp to me. So I'm assuming it's all normal.

The "nominal" battery voltage value was given on a website I consulted. But I also understand your calculation of the 3 series of the 4.2V pack which equals 12.6V.

Like I said, it all depends what you consider 'nominal' - the nominal voltage of a car battery is usually considered to be 13.8V, but some people have other opinions, and it's still known as a 12V battery Likewise AA batteries etc' are considered to be 1.5V, but they are more than that when new, and less than that when used.

Basically there are a considerable number of 'correct' values, don't just pick one and consider anything else is 'wrong'.

 

[wilder1626]

Thanks again for your clear explanations. It makes perfect sense.