[Q] Reverse charging specification

ColorSageColorSage Level 3
edited September 2020 in ZenFone 6


As I have already mentioned it one or twice I use my phone from time to time to charge other devices. The maximum speed I get is 500mA/5V for other phones and up to 870mA/5V while charging JBL Flip 4. These are typical charging rates using OTG adapter (<5W). In some reviews it is said to support up to 10W Reverse charging which is 2x my maximum charging ever measured. Is it really 10W or it's some kind of error? If not, how can I achieve faster charging rates? I'd expect something around 1.5A/5V.



  • kikolykikoly Level 6
    edited September 2019


    ZenFone 6 does not plan reverse charging function, it is not encouraged to use it~

    If you still insist on using reverse charging, 5V/0.5A is normal.

  • It run with 10w.

  • This is interesting as person from Asus already stated above it doesn't. How did you achieve that output?

  • That said it was 10w during the launch back in May

  • Yeah, I've figured they scrapped that feature in the meantime :/

  • OK look carefully

    5.005V at 0.25A

    4.970V at 0.50A

    4.936V at 0.75A

    4.900V at 1.00A

    4.868V at 1.25A

    4.832V at 1.50A

    4.75V at 1.68A

    Anything below 4.75 is out of specs.

    Technically USB voltage output is out of specs at 1.68A, we got 7.98W, which is under expected value, but it depends on the cable for the voltage loss and when the device being charged deems it should not draw more current by observing the voltage at the device end. Main problem is that the output is always targeting 5V as output, whereas some faster chargers raise the output to 5.3V under high current scenarios. Asus doesn't do that, and some devices charge very slowly.

  • Thanks. That would explain JBL's faster charging as it was charging at about 4.9V. That's a weird power supply solution. 0.25V decrease and 1.5A more. A bit counter intuitive if you ask me.

  • More data are coming in

    Xiaomi power bank, (used to show proper QC3.0 curve in previous posts, known to obey USB specs tightly) among other phones: 4.9737V, 0.4716A

    Blue Power Bank (the faulty QC powebank I mentioned is some of my previous posts, known to not obey USB specs): 4.8660V, 1.2430A

    DIY power bank (probably does not obey USB specs) : 4.8124V, 1.5075A

    From this information and the ability of the phone to transmit data from the port, it seems like the USB D+ D- lines are not used to incidate to the device to be charged that this power source is able to deliver more than standard USB specs (5V 0.5A). Well, phones and specs-obeying devices won't charge more than the limit. The point is further proven with the use of a dongle that shorts the D+ D- lines to trick devices into BC1.2 spec. Phones and power banks in the first section charge up to 4.9116V, 0.9010A now.

    Asus, If you can, next time market your phone more conservatively as 7.5W power output, and not 10W charging.

  • It's sad I can't use it to charge my peripherals with reasonable speed on the go. None of my devices charge with voltage lower than 4.92V while all phones are 5V+

This discussion has been closed.