Slow/Fast USB Charging iPAQ rx3715

[pnjm]

Hmm, I searched thru 2 pages and saw that no one seems to have asked this question yet: am I really that dumb? ;-)

This is the question:

The rx3715 has a facility for USB charging ie. no need for a separate power cable and connection to the power outlet, just charge the PDA via your USB port on your PC. I love it because I can charge my PDA off the USB on my office PC without having to invest in another power cable. I keep my power cable in my bedroom at home.

Thing is, the USB charging facility allows the user to pick "Slow" or "Fast" charge. This puzzles me. Why two charging speeds instead of one? To ask the same question in another way, what is the advantage or disadvantage of one charging speed over the other?

PN
(used to be NEC Mobile Pro P300 user. Still own it, but don't use it no more.)

[Menneisyys]

Personally, I haven't read the manual of the PPC in question (writing from a PL720 over GPRS so it'd be very slow for me to download and read it) . However, this seems pretty logical to me.

Most USB ports are only capable of supplying 0.5 Ampers. However, present-day Lithium-based PDA batteries may be charged with 1-1.5 A's as well. Maybe this is why there's an option for "fast" charging - there are USB ports that allow for currents far higher than the standard 0.5A.

If you give a try to the 'fast' mode, and find it that the desktop "drops" the USB port in a short time, only allowing to see it again after a reboot, then, your desktop isn't capable of supplying "high" currents. Otherwise, you may use it. (Hope the internal conductors on the motherboard will also stand the high current - do it at your risk etc.)

[TheOrange]

I own an rx3115 and stumbled across that same option. Infact, I do the same thing (power cable on the night stand, sync cable @ work). I set mine to fast charge and haven't had any problems. I haven't really played with it though, to see if one charges faster than the other. All seems fine so far though.

[pnjm]

Hi,

Sorry - clarify a little bit here - exactly how do I know if the desktop "drops" a USB connection?

If I understand you correctly, if I can activesync my PDA via its cradle plugged into the PC's USB port without any problems while the PDA is set to fast-charge, then that means no problem. Unless, of course, after a while the PC crashes on me altogether because although the USB port can handle the higher current without problems, the PC's power supply is not up to the task. Am I correct?

PN

....(snipped)....If you give a try to the 'fast' mode, and find it that the desktop "drops" the USB port in a short time, only allowing to see it again after a reboot, then, your desktop isn't capable of supplying "high" currents. Otherwise, you may use it. (Hope the internal conductors on the motherboard will also stand the high current - do it at your risk etc.)

[Menneisyys]

Hi,

Sorry - clarify a little bit here - exactly how do I know if the desktop "drops" a USB connection?


I meant the PC won't "see" the USB client at all if it draws more current than the USB port can supply, unless you reboot. It's built in into some PC's to avoid hardware damage, resulting from as high as 1.5-2A currents.

[pnjm]

Right! got that, thanks.