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#1 2020-05-31 14:13:31

grog
Member
Registered: 2020-05-31
Posts: 3

Thinkpad T540p lower wattage charger

Hi,

I installed ArchLinux on a Lenovo Thinkpad T540p. I fully encrypted the hard drive and I use GRUB as bootloader. I would like to use a 20V - 3.25A charger instead of the original 20V - 6.75A when traveling. Everything works flawlessly with the 6.75A charger. The 3.25A charger (original from Lenovo) charges the battery when the laptop is powered off, hibernated or suspended. It does not charge the battery when the laptop is running, and this is the problem I would like to solve.

I tried the 3.25A charger on the same laptop model running Windows 10, and it does charge the battery when the laptop is running.

Can anyone help?

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#2 2020-05-31 19:50:33

andym
Member
From: France
Registered: 2019-01-16
Posts: 45

Re: Thinkpad T540p lower wattage charger

This sound a bit weird. How do you know that the battery charges under Windows 10? How do you know that the battery does not charge under Arch when the laptop is running?

You can see all the battery data under /sys/class/power_supply/BAT0/ or may be BAT1

Check the values of current_now and charge_now. Current_now is the discharge rate and Charge_now is the level of the battery.

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#3 2020-06-01 10:10:01

grog
Member
Registered: 2020-05-31
Posts: 3

Re: Thinkpad T540p lower wattage charger

Hi

I know that the battery charges with the laptop running with Windows 10 because I plugged in the 3.25A charger into a ThinkPad T540p running that OS (a different machine from mine). As soon as I plug in the charger the icon in the bar shows that the machine is connected to the grid and the battery percentage starts to (slowly) increase until a full charge is reached.

When I plug in the same 3.25A charger into the ThinkPad T540p with Arch installed while the machine is running, the green light in the power button blinks three times and nothing else happens. The battery icon (GNOME desktop environment) does not show that the charger is plugged in (while it does if I plug in the 6.75A charger) and the battery percentage keeps going down.

This is the output of 

 cat /sys/class/power_supply/BAT0/uevent 

with the 3.25A charger plugged in:

POWER_SUPPLY_NAME=BAT0
POWER_SUPPLY_STATUS=Discharging
POWER_SUPPLY_PRESENT=1
POWER_SUPPLY_TECHNOLOGY=Li-ion
POWER_SUPPLY_CYCLE_COUNT=0
POWER_SUPPLY_VOLTAGE_MIN_DESIGN=10800000
POWER_SUPPLY_VOLTAGE_NOW=11657000
POWER_SUPPLY_POWER_NOW=12904000
POWER_SUPPLY_ENERGY_FULL_DESIGN=56160000
POWER_SUPPLY_ENERGY_FULL=43300000
POWER_SUPPLY_ENERGY_NOW=33140000
POWER_SUPPLY_CAPACITY=76
POWER_SUPPLY_CAPACITY_LEVEL=Normal
POWER_SUPPLY_MODEL_NAME=45N1147
POWER_SUPPLY_MANUFACTURER=LGC
POWER_SUPPLY_SERIAL_NUMBER=  247

The battery is discharging.

Same command with the 6.75A charger plugged in:

POWER_SUPPLY_NAME=BAT0
POWER_SUPPLY_STATUS=Charging
POWER_SUPPLY_PRESENT=1
POWER_SUPPLY_TECHNOLOGY=Li-ion
POWER_SUPPLY_CYCLE_COUNT=0
POWER_SUPPLY_VOLTAGE_MIN_DESIGN=10800000
POWER_SUPPLY_VOLTAGE_NOW=11610000
POWER_SUPPLY_POWER_NOW=0
POWER_SUPPLY_ENERGY_FULL_DESIGN=56160000
POWER_SUPPLY_ENERGY_FULL=43300000
POWER_SUPPLY_ENERGY_NOW=32110000
POWER_SUPPLY_CAPACITY=74
POWER_SUPPLY_CAPACITY_LEVEL=Normal
POWER_SUPPLY_MODEL_NAME=45N1147
POWER_SUPPLY_MANUFACTURER=LGC
POWER_SUPPLY_SERIAL_NUMBER=  247

The battery is charging.

In my opinion the firmware is ok with the 3.25A charger because the battery charges when the laptop is powered off, hibernated or suspended. But when Arch is running there must be a setting somewhere stating a minimum acceptable power input from the charger, and this overrides the firmware. But this is just my hypothesis.

Last edited by grog (2020-06-01 18:15:30)

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#4 2021-04-30 13:16:34

grog
Member
Registered: 2020-05-31
Posts: 3

Re: Thinkpad T540p lower wattage charger

I concluded that it is a firmware issue. The ThinkPad T540p that works flawlessly with the 3.25A charger does not have a dedicated graphic card. The machine that does not recognize the 3.25A charger does have a dedicated graphic card, so it probably has higher power requirements specified in the firmware.

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