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Current consumption of the Kobo Libra H2O
Measurement of the current consumption in different modes
I bought a Kobo Libra H2O, which works very well, but I found no clear information about the balance between power off and standby modes.
Kobo presets the device with 15 minutes auto-standby and 60 minutes auto power-off, but which is the actual consumption and when should I manually turn it off?
To solve the issue I used a VC9808+ multimeter to measure the current consumption in standby and power off mode and I used a DPS5005 adjustable power supply to provide power to the device.
First I completely charged the battery, see the charging icon:
Then I took photos of the current consumption in standby and in power off modes, which are respectively 38 mA and 2 mA:
The power consumption in poweroff was measured also with a multimeter and the result was around 1.5 mA.
To know at which point standby is more convenient than a power off followed by a reboot, I took a video of the power supply during boot and I copied the values read to a spreadsheet, then I calculated the average value. In the video the end of the boot takes place when the current consumption stabilises at around 90-100 mA, even if usually the current consumption in power on, but idle mode is around 40 mA.
The average current consumption is 203 mA and it takes about 45 seconds for the current consumption to drop, so it's about 9100 mAs.
After some thinking, these values cannot be reliable: if the standby really used 40 mA, it would drain the 1200 mAh battery in 1200/40=30 hours, which is not the case. The poweroff consumption of 1.5 mA may be more realistic, since it would translate into 33 days, which is in line with "weeks" of battery life as generically stated by Kobo.
It is likely that in standby mode, with power connected, the processor remains active, using more current than they would when battery powered.
Another test, in fact, showed that the device, when in use but without any page turning, stabilises around 40 mA (not shown in the video). It was difficult to reproduce with the setup I had because the processor tries to charge battery any time it gets connected, so the measurements would take long time.
A better test that I may triy is to leave the device in standby mode for few days and write down the battery usage, then I could repeat the test in power down and also write down the percent of battery consumption. Given the realistic results of the poweroff and of the boot process measurements, using the ratio an estimate could be obtained.
The only issue is not being allowed to use the device for a whole week, more or less.
Author: Olaf Marzocchi
First revision: 2020-08-08.
Last revision: 2023-07-23.