Ace: Charge via USB without Drivers

[LiquidKernel]

This seems to be an interesting problem that's very common amongst smart phones.

The USB cable and regular wall charger use different pins for the 5 volts necessary to charge. It is assumed that the wall charger can provide enough current to do a rapid charge, so it can charge right away. The USB charger, since powered from the USB host (computer), may not provide enough. So the phone talks to the computer to confirm the USB host can provide the juice, and then tells the charging circuit to enable rapid charging.

Now, the reason I ask.

I got one of those cigarette lighter to USB adapters so I can use my USB cable to charge the phone (I find the wire cleaner than the coil wire of my broken OEM charger). When I plug my phone into it, it doesn't show it as charging when on (and doesn't beep), but if the phone is off, it'll show the usual charging screen. Now what I think it's doing is a trickle charge by default.

I tried plugging my phone into the USB of my laptop without my computer bootup (just on and before Windows starts) and the phone won't charge either. Only once the USB host is enabled (drivers loaded) does it go into rapid charge mode.

What I am wondering, if this is something Windows Mobile handles, can it be disabled? Or is this the charging hardware?

PS: Pulling the two data pins of the USB up to 5V doesn't help, I tried it with a separate USB plug with a few resistors and took apart the charger I bought.. both pins are pulled up to 5V with a pair of 200K ohm resistors.

[deathgrind]

Not completely sure on the car charger but I know when you have your phone plugged in to USB port on your computer it won't usually start charging until after your computer starts up. Usually when my phone is plugged into my computer if I go to reboot or something my phone will light back up as if the charger had been unplugged for the power source. And then when I log back into my computer it will beep and start charging again. So I think this is normal for most phones because I had another phone through a different carrier that did the same thing.

[LiquidKernel]

Yep, that's what happens. The phone is talking to the USB host to confirm it can provide enough current. No matter what car USB charger you use this will happen, unless you use a different cable or disable it on the phone. I'm trying to figure out how to have the phone stop checking.

[recithree]

interesting to find this thread.i went through this the other day with my motorola q9c.i needed my phone near me so couldnt leave it on car charger.
since i working in a data center there was plenty of pc's around.when i plugged into pc i got what you have seen,a charging screen only if phone is off.i left it that way for at least a hour and i dont think it was even trickle charging.
so then i found a couple of wall chargers that had a usb end to match phone.each one of those gave a non motorola charger warning.
and then,my parter had a plug in device he usedwith his ipod touch that accepted a usb cord.i tried that and it would not charger either but his tmobile dash would.personally the only one that had even cooperated with me was a belkin charger.(besides a motorola one of course)
so the end of the story is i left the phone in the car and missed my call.

[monkeyboy]

I really doubt there is any true "talking" involved, perhaps more like grunts and groans :) AFAIK there is no charging/handshaking protocol. Instead there is probably a multistate charging sequence within the phone, which basically tests how much current is available. The source just delivers what it can and has no "intelligence".

In the case of the car charger, if it only can deliver 300-500ma, then if your phone is ON, that sucks up a fair bit of the available current such that there is not enough left over for the charging protocol. Presumably you are talking about non-OEM chargers. Some of them are REALLY crappy and are nearly worthless. In any case you really want to buy chargers that can supply at least 1000ma at 5V.

Whether your phones uses a different circuit for the AC charger vs a USB charger -- I doubt it, although it is possible and of course would depend on the particular phone you are talking about. But for example, many HTC phones simply use a mini-USB (and other phones use micro-USB) connectors for charging -- there ARE no other circuit paths available. And there is nothing special about an AC charger vs a USB charger. AC charger can be just as crappy and unable to deliver a full 1000ma as USB chargers.

Typical USB ports on laptops only deliver 500ma, so yes, they are going to charge more slowly. Yes, that power is only available if the laptop is turned on. But it has nothing to do with "talking" to the laptop. You can easily demonstrate this by buying a USB charge-only cable (only 2 conductors, $1 at the dollar store). It will behave in the same way even though there are no data connections to use. Or don't install the USB driver for that phone on your laptop (or run DOS or whatever). The charging behavior will still be the same. No software is involved.

In summary, most of the funky behavior you're seeing has to do with how crappy the cheapo chargers are that are commonly sold. A good solid AC or car or USB charger that can deliver a stable 1000ma at 5V and all these weirdnesses will go away (I bet)...