8

The big problem: Like a lot of people, we are finding that our tablet does not maintain charge when connected to USB (PC or other device, not AC jack, we need data and charging simultaneously).

What has worked so far: On two tablets, we have been able to successfully force the tablet to draw a higher current by writing a higher value to the files

  • on Acer Iconia Tab 8: /sys/devices/pci0000:00/0000:00:18.1/i2c-1/1-0035/power_supply/smb34x-usb_charger/
  • on Samsung Galaxy Tab A: /sys/devices/soc.0/i2c.65/i2c-13/13-0066/max77849-charger/power_supply/max77849-charger/

on those tablets in the above directories, after setting the appropriate permissions (Acer: chmod 777 input_cur_limit, Tab A: chmod 777 current_now) we can change the USB charge current by writing to the files with the commands:

  • Acer: echo "1000" > input_cur_limit
  • Tab A: echo "1000" > current_now

This works great on these two tablets. An inline meter on the USB shows the current going higher (close to 1000mA, or whatever we specify) and we are not frying anything (PC, OTG device, tablet) and when the battery fills up itself regulates to a lower value. All good.

The Problem now: We have a new tablet. The Samsung Galaxy Tab 4 - 7" (also tried on an 8" with the same results).

We found the file we thought we should modify:

  • current_now in sys/devices/platform/3.i2c/i2c-8/8-0049/power_supply/sec-charger

We changed the permissions and used echo "1000" > current_now to try and modify the file and nothing happens. It keeps returning instantly back to 450 and the meter reading does not go up.

Any ideas? It worked on the first two devices we tried, but not on these last two (Tab 4 - 7" and 8"). Maybe someone has a completely different method? Maybe there is another file to change (we have tried several other similarly named files). We understand that this breaks the USB 2 spec, but we need to charge the tablets and send data at the same time.

  • 1
    I gotta refresh my memory (look for it), but I think there's a kernel/acpi option that prevents certain power-related changes by default (on laptops). The idea being that if it's really needed, the potential dangers associated with these hacks will be made known to the user; and if it's worth pursuing it's really needed. – ILMostro_7 Nov 24 '15 at 22:50
  • What's the directory listing of /sys/devices/? # ls -alh /sys/devices/ will list the contents. There might be a platform-/vendor-specific way to enable/disable this. – ILMostro_7 Nov 26 '15 at 8:29
3

This is to point out a possibility of replacing echo option, with a copy paste option

( Before that, here is a similar search Prevent complete charging?. .)

Related efforts and success for AC charging by replacing the file itself, when echo was not possible, (for reasons I still don't know) is my answer for Honor 6 phone here How do I override charging current on Huawei Honor 6?.

On a side note, similar effort for Samsung Note 2 https://android.stackexchange.com/questions/127288/over-ride-charging-current-on-note-2-n-7100 has not yielded a solution. Unconfirmed views are :

  1. Kernel alone can do that for this phone (from two kernel chefs who made kernels for this phone)

  2. Chipset limitations. This from a developer

Since their views are based on email, cannot quote names

All the best and will be looking to find if there is yet another way

  • Some one else in the office has tried the copy and paste method (just found this out now, didn't know they had already tried it to no avail). Thanks for the suggestion though. I hadn't found too many references to other people trying similar methods, so thank you for those links. – JimAtRaven Nov 24 '15 at 21:21
  • Have you found a way out yet? If yes, please update for benefit of others. If not, have a look at this to do the opposite-May give you some clues android.stackexchange.com/a/133984/131553 – beeshyams Jan 11 '16 at 15:29
  • 1
    The suggested solutions did not work for the tablets in question. The methods worked on some tablets, so we selected a tablet for which the method I described in the original question worked. As far as I am concerned there has not been a general answer provided (and there may not be one). Having moved on, I hope my question and the posted suggestions help some people, but non are yet deserving of being considered THE answer. – JimAtRaven Jan 16 '16 at 22:45
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Don't modify anything in the device to change its power settings.

You need to connect it to a port that can provide the desired level current. You don't make the device draw more current.

On a PC, some motherboard USB ports can provide more current. Check your PC motherboard's manual. If you don't have that, then you can try this. From the OS, shut down the PC. Do not cut the mains power supply to the SMPS (motherboard). Now, connect your tablet or any mobile phone to each one of the ports on the PC. The ports that are designated for device charging will charge device. Others will be switched off by software. Sometimes, the device charging USB headers on the motherboard may not be connected to the ports. You may have re-map the cables or add additional ports that connect to them.

http://www.gigabyte.in/MicroSite/185/on-off-charge.htm

The simplest way to charge tablets is to use a wall charger.

  • Unfortunately that's not necessarily how it works. We have devices capable of supplying a higher current but if the tablet is obeying the USB spec it will not request more than 500mA while a data connection is open. Sure a wall charger will send more current because to tell the device that it is a wall charger it shorts the data lines. This defeats our requirement for data and higher current simultaneously. We have had success on breaking the spec on some devices, but not the one we want. Hence my question. I appreciate your input, but unfortunately this will not work for us. – JimAtRaven Nov 30 '15 at 14:04

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