0
\$\begingroup\$

I've an ATX power supply and I'm trying to charge my Nexus 5 phone.
I connected USB female (from an old PC) to +5V and GND and shorted the DATA+ and DATA-.
My multimeter shows 0.400A when I connect my phone.
I tried to put 1k ohm resistor (that's what I found) and then it showed 0.600A but my phone shows around 0.200A on both. The original charger output is 1.2A and on the phone it shows 0.800A.
I can't find what's the problem, my ATX PSU can give up to 36A on the +5V (Red wire) rail and my phone won't draw more than 0.200-0.300A. What am I missing?

\$\endgroup\$

closed as off-topic by Leon Heller, Daniel Grillo, Dave Tweed Aug 11 '15 at 12:36

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Leon Heller, Daniel Grillo, Dave Tweed
If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ I hope you don't expect your phone to draw 36A. That's just silly. \$\endgroup\$ – KyranF Aug 5 '15 at 21:52
  • 1
    \$\begingroup\$ If your multimeter shows 600mA flowing, then 600mA is flowing. And just shorting D+ and D- does not conform to the USB charging spec, iirc. \$\endgroup\$ – Passerby Aug 5 '15 at 21:57
  • \$\begingroup\$ @KyranF, of course not. I'm not THAT stupid :) I'm just trying to understand why it's won't draw 800ma like it's drawing from the wall charger.@Passerby That's what I found online, to use the fast charging it should be shorted or used with resistor. \$\endgroup\$ – Adam Aug 5 '15 at 21:59
  • \$\begingroup\$ Try the samsung setup cdn-images.xda-developers.com/direct/1/9/5/4/3/0/8/… \$\endgroup\$ – Passerby Aug 5 '15 at 22:03
  • \$\begingroup\$ Phone charging is artform, like witchcraft. There is also the apple setup which most newer android phones will accept. And some phones require that the usb shield be tied to ground on both ends, so some usb cables charge slower than others. Its a pain \$\endgroup\$ – Passerby Aug 5 '15 at 22:04
2
\$\begingroup\$

shorting D+ and D- indicates to the PD (portable device) that it is connected to a DCP (downstream charging port) and is allowed to draw up to 1.5A. It's all in the USB Battery Charging spec (google BC1.2). What are you doing with the 1k resistor? Are you using your multimeter correctly (in series with the circuit). What do you mean by "my phone shows"? Forget your phone, the multimeter shows the truth. Also know that your phone will draw a different amount of current depending on where it is in the charging cycle.

\$\endgroup\$
  • \$\begingroup\$ I tried to put the 1K resistor instead of the 200ohm (many says that 200ohm should solve it but I don't have 200ohm within reach so I used the 1K). I'm using an app called "Ampere", the app subtracting the draw of the phone (4G, screen etc.) from the charging current, so if I see on the multimeter (yes, I know how to use it to measure current) 400mA and my phone draws 200mA for the screen and 4G the app will show 200mA. my goal is to see on the multimeter a draw of 1.2A or at least 1A like the wall charger. \$\endgroup\$ – Adam Aug 6 '15 at 6:28
  • \$\begingroup\$ When you say "put the 1k resistor" you need to be more specific. Where are you putting it? \$\endgroup\$ – mhz Aug 6 '15 at 18:12
  • \$\begingroup\$ Here's what I would advise you do if you suspect that the phone is changing it's current consumption on the ATX supply. Take your nexus 5 charger, cut the red wire (or build an interposer) so that you can take a current measurement with your multimeter. Then (with the phone in the exact same use case, same apps running, same brightness level, etc.) measure with your multimeter the current from the ATX power supply, with the D+ and D- shorted together. They should be roughly the same. \$\endgroup\$ – mhz Aug 6 '15 at 18:17

Not the answer you're looking for? Browse other questions tagged or ask your own question.