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I've recently got hold on an HTC One X having moved from an HTC Desire.

I noticed that my One X charges very slowly when connected to the USB socket on my PC, whereas the Desire was comparatively fast. When charging the One X from the supplied AC adapter the charge is very fast. So, I purchased a new Mains Adapter to keep in the office.

However, when connecting the phone to this mains adapter the device still says Charging : USB under the battery status tab and it isn’t as fast as I thought it should be

So, is there some difference between the supplied AC adapter and this third-party one I have purchased? Presumably the power supplied s not as high or is there something more?

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I would guess the one connected via USB isn't giving off power more than the direct AC. That's the case as well for my Xperia so I assumed it's a normal thing. –  Propeller Jun 18 '12 at 16:48

2 Answers 2

up vote 5 down vote accepted

To charge at the maximum rate, the charger must identify itself as a charging device by shorting two middle USB pins. This is in the USB specification. Proper chargers come like this. Other chargers can be modified to short the pins together.

I have personally modded a Griffin USB car charger in this manner. Before the change, it would charge in "USB" mode. After soldering together the two pins, the phone charges in "AC" mode.

One caveat: I have not done any tests to see if this changes the charging rate, but it certainly charges quickly after the mod. Everything I have read about this phone says that it will only pull 500 mA in "USB" mode.

References: Wikipedia entry regarding USB charging spec. Look for the words "Dedicated charging port."

Amazon user review with instructions for modding a certain car charger.

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Is there any reference that says they follow the USB.org charger spec? Apple, Sony, and HP do not. Do all HTC phones? –  endolith Feb 10 at 17:34

In fact the charging time depends on two points:

  1. the output current of the adapter or the USB. The output current of the PC is only 0.5a, it may charge slowly than most of the AC adapters (most of the AC Adapters are 1A or more).

  2. the input current and the charging convert rate of the phone. Different phones have different input current due to Limited current protection for them. For example, the limites current for Nokia is 0.5a, the input current is only 0.5a even you use an ac adapter with 1.0a output. Beside, the charging convert rate is also different according to the models.

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Thank you. This suggests that there is a difference in power output between the third-party AC charger I am using and the HTC branded AC charger that came with the device. The third party says it outputs 1000mA, so presumably this will still charge faster than plugging into the USB socket. –  Rob Jun 19 '12 at 10:19
    
@Rob: No, it will still charge at the slow speed. In "USB" charging mode the phone will only pull 500 mA. –  skypecakes Nov 9 '12 at 21:14

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