Thread: External Battery Packs
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j.s is offline j.s
2009-12-13 , 04:46
Posts: 486 | Thanked: 251 times | Joined on Oct 2009
#9
Originally Posted by Rushmore View Post
It appears there is some form of handshake going on to open a gate to charge. May be a standard that computers and some chargers adhere to and some other chargers do not comply with. The N900 is picky, but probably by design- for safety reasons.
A device is allowed to draw 100ma from a USB port by default. There is some USB signal protocol to allow a device to draw up to 500ma if the host gives permission. Many devices ignore this and try to draw whatever they want.

There is no standard for USB dumb chargers. Different manufacturers make up their own ad hoc method, often a certain resitance between certain pins. As you might imagine, different resistances and pins are used.

Openmoko published their method, it will be interesting to see whether Nokia does the same.
 

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