USB sync/charge cable warning - Page 2

*JakeRich* · 01-07-05, 06:26 PM

Originally Posted by Tuba

CLIP...

I assume the USB sync and charge cables will work the same as the USB cradle without the power cord. So I am now going to order the Gomadic cables.

CLIP

Fundamentally, your assumption may work IF the cable maker routes the 5v from the USB port to the same pins on the X50 socket that the cradle uses for the USB power. Unfortunately, I suspect that in their effort to be "sync and charge" at the same time, the cable makers have routed the USB power to the external power output pins. The symptom that they have done that is that the power light in the button will be ON when the Axim is ON. In the cradle, with only the USB connection, the charging light is OUT when the Axim is ON and ON when the Axim is OFF.

Dell probably knew that USB could not power the Axim and charge it at the same time safely, so they used separate input pins for USB and external power. On external power they appear to have assumed sufficient current was available, so you can have the Axim ON and the button will be ON at the same time. Unfortunately, if the USB power is routed to the external pin, the Axim has no way of knowing that the supply is insufficient, so it tries to charge and sync at the same time but the USB cannot keep up.

Tuba · 01-07-05, 08:39 PM

OK, I finally understand all this. Only had to read this thread about 20 times. Here’s my understanding, using layman’s terms and simple analogy:
The input slot on the Dell Axim has 2 pins to feed it power – 1 from your computer’s USB port (at +5 v) and 1 from the power cable (at +5.4v) that plugs into the wall outlet:

Cradle/Power Cable
Axim’s +5 v pin <== cradle’s +5 v pin <== USB cable (output +5 v)
Axim’s +5.4v pin <== cradle’s +5.4v pin<== Power cable (output +5.4v)

The cradle is setup this way and the Axim is smart. If you cradle the Axim without the power plug, it will only draw power from the USB port when the Axim is off. It knows that while the Axim is on, the +5 v from the USB doesn’t leave enough extra juice to charge the battery, except perhaps for a trickle charge. If the power cable is used, it knows it can operate and charge off the 5.4v of that line

The problem is third party USB sync/charge cables don’t use an external power cable. Instead, they channel any and all power from the USB port. The mistake is that they crossed the lead and feed the USB power (at +5 v max.) into a receptacle designed to eat +5.4v. Like so:

3rd Party USB sync/charge cable
Axim’s +5 v pin <== EMPTY (no cable pin, no power cable)
Axim’s +5.4v pin <== cable’s +5 v pin <== USB cable (output +5 v)

The Axim, when using a 3rd Party USB sync/charge cable, has a +5.4v appetite (pin) but only gets fed +5 v diet. If it sucks too hard, by needing juice to both charge the battery and run the Axim, it may zap the computer’s USB port or not eat enough to be full (i.e., charge the battery). The Axim doesn’t know to only draw power from this cable when it is off, as with the cradle and its two pins. It expects an ample (+5.4v) supply because it is coming in on the pin designated for the power cable.

Am I correct in my understanding?

Kenban · 01-09-05, 04:29 PM

I have finshed the first round of tests. Voltage was a little closer to 5v then I originally planned but I don't think it would really be effecting the current. I would be attaching a JPG with the curve on it but the board is limiting me to a 100kb 450x450 image and the one my software produced while I can get it in under 100k I can't resize it and have you still be able to read it so I need to plot the data in excel later.

The axim was off so all current mesurements are done over time and not the % charge of the battery. Tests were done on the 2200mAh battery and I will redo them for the 1100mAh battery soon.

Samples were taken every second for 10,000 samples (about 2 hours 45 minutes) by which time the battery was fully charged.

For the first 6,000 samples the current was pretty constant at 925mA then has a pretty steep drop until it reaches 100mA at around the 9,600 second. At that point the current dropped from 100mA to 6mA which showed the battery was fully charged.

The interesting thing is though the fact that for most of the charging cycle it was at 925mA which mind you is almost twice the current that a USB port should be able to provide and thats assuming the axim is off.

Hope to have some info on the 1100mAh battery in the next few days and need to get the curve posted so you guys can take a look at it.

*JakeRich* · 01-09-05, 07:24 PM

Tuba, your understanding is correct as far as we know. It's all based on Kenban's measurments and the way the thing operates, since Dell hasn't tols us how it works. One additional factor is that when the Axim thinks it has sufficient power, but doesn't, it can actually draw power FROM the battery to charge the battery. That's going to be a losing proposition, so the battery actually decays faster with that power than it would with no power at all.

Kenban · 01-10-05, 10:55 PM

I did a second test this time with a 1100mAh battery. I think this might help explain why some people seem to have more problems then others. The 1100mAh battery has a much lower charging current then the 2200mAh battery.

The charging started at 630mA and remained flat for most of the charging. I was watching the data from time to time and was able to notice when the current started to go down and turned on the axim to check the battery %. I found that it happened around 67% so I expect if you really want to use one of these cables and use a computer USB port you should have no problems at all if you leave the axim off, have a 1100mAh battery in it and the battery is at 70% or more

I still hope to post some pictures so you can see the power curve but this data should give you some idea of what kind of power you need. But if your having problems and are using a 2200mAh battery I recommend you try out the 1100mAh battery.

*JakeRich* · 01-11-05, 08:01 AM

Kenban, what's the power draw with the X50 on, battery about 50%? If it draws 630 mA to charge when OFF, and about 400 mA when ON, then logic says it should be near 1 A charging and On, which is the state these charge and sync cables claim to support. Of course, USB can't support that (unless you have a powered hub).

SolSie · 01-11-05, 08:35 AM

What do you think about this: http://semsons.com/unbaexwiusbp.html
5.6V @ 800mA output

Kenban · 01-12-05, 02:14 PM

Originally Posted by JakeRich

Kenban, what's the power draw with the X50 on, battery about 50%? If it draws 630 mA to charge when OFF, and about 400 mA when ON, then logic says it should be near 1 A charging and On, which is the state these charge and sync cables claim to support. Of course, USB can't support that (unless you have a powered hub).

It does draw around one amp. I tried it out with a 1100mAh battery mind you it all depends on what you have running and what the brightness of your screen is and your processer speed. I think I had the brightness up and the processer down at 208mhz.

(I took my own advice to someone else took a radio shack power bank used a high current diode to drop the voltage and can use it to charge the axim) If I draw more then an amp it cuts the current and I have to unplug it and wait a sec for it to reset. When charging the 2200mAh battery I can't turn on the axim if I am charging the 1100mAh battery I just need to keep the processer speed or the screen brightness down and it works just fine.

SolSie I think even though the voltage is a little high you should be fine on that end BUT the 800mA output might be a little low you could charge the 1100mAh battery BUT not the 2200mAh battery. Also you would have to leave the axim off during charging. Although if the battery is charged you should be able to use the axim off that supply with no problems.

*JakeRich* · 01-12-05, 06:28 PM

Kenban, I've seen the internal diagnostics hit over 600 mA at full brightness and full speed with WiFi on. With a dead-ish 2200 battery and another 625 mA to charge, I can see why Dell sends a 2 amp power converter!

SeanX · 01-14-05, 02:25 AM

I just got my sync and charge cable. Turn sout to be a sync and discharge cable. Sucked my battery down to 50% in 30 minutes. I am trying to get a reply from sendio now.

Kenban · 01-17-05, 05:06 PM

I have said a few times now I would post a picture of the charge curves and here is an attempt

the only problem is you still can't read it

But it should give you an idea of what I have been talking about.

The pink curve is the 2200 mAh battery
Dark blue is the 1100 mAh battery
Up the left side of the graph is current in amps each line is .2 amps. That big spike in the 1100 curve is when I turned the system on to check the % battery charge.
Time goes accross the bottom of the graph in seconds.

I do have a really nice excel document with all this data in it now

zim2dive · 01-18-05, 01:20 PM

great info, but LOL, I guess the burning question is when/where can we all buy a $2 cable that is safe to use??

Mike

gringuito · 01-18-05, 06:10 PM

Hmmm ok I bought a set on ebay with a wall charger unit, on the wall charger it says Output: 12Vdc, 400mA, 3.6W (MAX) Does that mean I'm not going to get enough juice to charge my battery because it only is letting out 400mA?

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