USB Charging/Sync Cable draining battery?

11-24-03, 11:48 AM

I have the Belkin travel/sync package that you can get from Dell.

I use the USB sync/charge cable at work. My battery was about 50% when I got to work so I hooked up the cable which is connected to my computer. I was watching the battery monitor and it actual started decreasing all the way to 0!

It counted down backwards in about 5 seconds until it reached zero. Now I know it didn't actually discharge the battery, becasue as soon as I disconnect the cable the battery meter quickly goes back up to 50%.

I know that it isn't a problem with the cable because I then connected the cable to the wall adapter and it's charging just fine now.

Now I know that when using USB cables to charge the Axim through the computer, you don't receive much of a charge, and if the battery is too low it just won't do the job.

But I was really surprised to see the battery monitor slide all the way to zero?

Why does this happen?

JakeRich · 11-24-03, 01:58 PM

The Axim requires quite a bit of power to charge the battery. The wall plug is rated at 2410 mA, for example. Even the car chargers are rated at 850 mA or more.

USB ports are only rated to 100 ma, possibly 500 mA if the manufacturer decides to push the upper limit. So, the USB charge cables WILL discharge the battery in certain circumstances. The way the battery charges depends on the remaining power. As the remaining power declines, the charging demand increases. At about 70% the demand for power exceeds the standard USB port's ability to provide. Apparently the charging circuit continues to make demands, so the battery steps in to provide the demand. Of course, now you have the battery charging the battery so the draw is much higher and the battery discharges faster and faster.

The moral of the story is to use the USB cable only when the battery is 70% or more. Below that, on a standard USB port, you are going to be in a losing battle.

11-24-03, 02:07 PM

Makes sense...Thanks for the answer.

11-24-03, 02:28 PM

There have been several threads on this, you should be able to do a search and find them.
Jake is right, not enough "juice" in the sync cable, Dell says it needs 5.4 V and 2410 mAmps.

PsionMan · 12-20-03, 11:59 AM

MY experience would appear to confirm this. I've noticed that sometimes when I try to charge the Axim from my laptop over the USB cable the battery charge 'appears' to drain to about 7%. I've tried charging the Axim in my car (still using the USB cable with the cigarette lighter adaptor, and the charge IMMEDIATELY jumps to 67%

Thanks for the help, this'll make it easier to control battery levels

RobertCF · 12-23-03, 11:54 AM

I could go into a whole diatribe about Dell's somewhat hidden issues with USB and their PocketPCs (something I've battled with of late) but I might suggest that a powered hub might fix that problem even when the battery is low. I've seen that most onboard USB ports just don't have the power for more than one solid item. Some third party cards are able to help a bit, but I think a powered hub does better because it has dedicated power.

rtalain · 12-23-03, 02:05 PM

This may seem obvious, but from what I've read, in order to charge through USB, the unit needs to be off.

Ron

Raynne413 · 12-23-03, 02:20 PM

The USB sync cable will only charge if the battery percentage is about 80%.