| Dale DePriest 2007-05-29, 12:33 pm |
|
Mr Physics wrote:
> Ron Hunter wrote:
> It would be an error to assume that all 'USB' chargers or power sources
> are the same. The charger for my Motorola Razr will not charge either my
> wife's Blackberry or my GPSMap60cx. 5V power and a common connector do
> not a standard make, unfortunately. As far as I can tell, the best that
> can be said about this is that mixing and matching chargers will
> probably not harm charger or device. I seem to remember reading that
> this is a result of certain pins other than +5V and GND on the USB link
> being held, high, low, or left to float to tell the device that it
> should be in charge mode. Sometimes engineers are too smart for our own
> good.
> Greg
The reason that this is true is that the standard for USB is very
limited in the power it can supply. A USB connector is only guaranteed
to be able to supply 100 mA and generally cannot supply over 500 mA.
Many GPS devices need more than this and if unchecked they might break
the hardware in your computer. That is the downside of using USB style
connectors for charging or powering tasks. USB was never designed for a
charging task but people like to use if for this so the designers have
come up with all kinds of techniques to detect is a real computer is
hooked up so that they can reduce current requirements of the device to
avoid destroying your computer. This is why a connector and 5V don't a
standard make. The engineers are not out to get you, they are trying to
protect you or your computer.
Dale
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_ _ Dale DePriest
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o/_/ (_(_X_(` For GPS and GPS/PDAs
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