Droid Charging Requirements

[RTAdams89]

I have several USB-MicroUSB cables (some OEM Motorola, some other brands), several 12 volt-USB converters, several cars, and several devices that accept MicroUSB connection for power. With everything other than my Droid (including a Blackberry and a GPS unit) every combination of cable and 12volt converter works. With the Droid, all of the combinations will turn on the screen (indicating the Droid knows a cable has been connected), but only a few combinations will actually charge the Droid. The only possible explanation I have come up with for this is that the Droid has some sort of minimum current requirement, and that some converter/car/cable combinations are unable to meet this requirement. So, what is the minimum voltage and current that will allow the Droid to charge? And, does anyone have any other ideas about this?

 

[RTAdams89]

PS: I know that the charger that comes with Droid is 850mA. I also know that the Droid charges form my computer (about 500mA). The car charger I have that works with the Droid is 1000mA, and the one that doesn't is unlabeled. Anyhow, I am just wondering what the very minimum current is that will still allow the Droid to charge (even if it is slow).

 

[Szadzik]

PS: I know that the charger that comes with Droid is 850mA. I also know that the Droid charges form my computer (about 500mA). The car charger I have that works with the Droid is 1000mA, and the one that doesn't is unlabeled. Anyhow, I am just wondering what the very minimum current is that will still allow the Droid to charge (even if it is slow).

The minimum will have to be a tad bit higher than the maximum power consumption of the phone. So that when you connect it to the charger it gives more power than is consumed by the phone.

 

[darrenxes]

I have been using nokia cable for e71 to link up my dext as well.. No issue

 

[RTAdams89]

The minimum will have to be a tad bit higher than the maximum power consumption of the phone. So that when you connect it to the charger it gives more power than is consumed by the phone.

Not sure about that, but care to hazard a guess and quantify the value?

 

[Szadzik]

Not sure about that, but care to hazard a guess and quantify the value?

If a computer that is capable of outputting a max of 500mA can charge it I think the max usage would be at around 350mA with everything on etc.

I do not think however you will find a charger with less than 500mA output so I would not worry about it. Just use whatever you have or tell us what you are trying to do.

 

[RTAdams89]

It's interesting: with the default Motorola USB cable the droid charges fine from my computer's USB port, but using another cable (which does "work" as it charges something else) won't charge the Droid.

 

[Szadzik]

It's interesting: with the default Motorola USB cable the droid charges fine from my computer's USB port, but using another cable (which does "work" as it charges something else) won't charge the Droid.

Different pin connections. There may be manufacturer specific cables that are a bit different from the standard ones and thus not work.

 

[RTAdams89]

Different pin connections. There may be manufacturer specific cables that are a bit different from the standard ones and thus not work.

The Droid uses a standard MicroUSB conenctor, no?

 

[Szadzik]

The Droid uses a standard MicroUSB conenctor, no?

Yes, but the cable you have my be non-standard.

 

[c670809]

I just built a charger so I could use aa's to charge the phone in-case I was in an area without power.

At first I hooked it up like the 'standard' usb connection should be with + and - pins on the outside. I tried it and it would turn the phone on but would not charge. So, I looked at the AC charger that came with the phone. . . the two center pins are connected. So then I connected mine and it works great.

I know apple does something tricky like that too.

Matt

 

[RTAdams89]

the two center pins are connected. So then I connected mine and it works great.

As in the two center pins are connected to each other, thereby creating a short between what are normally the data pins? WTF, that seems like a dumb design idea...

 

[dmodert66]

A better place for this may have been in the Droid forum. IIRC there where a few threads about this very issue there in the past. Hope you get it sorted though!

 

[c670809]

As in the two center pins are connected to each other, thereby creating a short between what are normally the data pins? WTF, that seems like a dumb design idea...

I know it sounds crazy, but yes, that is exactly what I mean. It's pretty easy to test. Plug in your AC power supply, unplug the USB cable, now with a volt/ohm meter measure it the power supply. The outside pins will be + and - . . . now set your meter to ohms and the two center pins are just connected together.

Now as a disclaimer . . . this is how mine is but you need to check yours.

Matt

 

[RTAdams89]

I'll certainly look into this. Is this the "EMU" (aka "enhanced micro usb") connector that Motorola uses? I've heard about it before (and just now researched it more), but I didn't realize it was so sophisticated.

As a follow up, if this is an EMU setup, then as I Understand it, shorting the two data pins tells the Droid "you are connected to a wall charger, not a computer" and the Droid then attempts to draw more current than the 500ma a USB port can provide. Does anyone know what the maximum current the Droid will draw when it knows it is connected to a computer (500ma, or something less)? How about the maximum when connected to a wall charger?

 

[c670809]

I wish I could help more . . . I did all my testing with the original cable and the OEM wall charger.

I only know that when I plugged the original cable into the 'usb battery' that I made it didn't work. When I measured the OEM charger and then shorted the middle leads on my usb, then everything worked fine. Without the cables shorted it would turn the phone on but it would not charge it.

I have not tried to see how much the phone will pull but my supply will put out 1.5 amps.

Hope this helps.
Matt

 

[RTAdams89]

That is bizarre. So you have a power source that is capable of outputting 1500ma, and when you connect it to the Droid via a USB - MicroUSB cable, it will only charge if the two data pins are shorted? Since the data pins are obviously not shorted on a computer's USB port, how then does the Droid charge when connected to a computer?

Any ideas where I might find more info about this whole deal?

 

[RTAdams89]

Wikipedia had this to say about the EMU connector:

Some mobile phone companies have used the extra pin "X" to enforce the use of their own battery chargers. Verizon Wireless is the first company to require first-party battery chargers, having colluded with Motorola[citation needed] to put an arbitrary 1.4 volts on pin X. This voltage violates the USB-IF standards, as pin X should either be tied to ground or not connected at all. Without this connection, the phone will refuse to charge, displaying "unauthorized charger" despite receiving the proper current. The phone will charge while connected to a personal computer only if the PC is running a special device driver.

Since my Droid seems to charge with some card chargers and from my computer's USB port even before Windows is loaded, I'm not sure how accurate those statements are.

 

[KlaymenDK]

Hi all,
I can see you've been doing a fair bit of research -- but you've just missed the true reason!

The USB protocol specifies that any ole device should be allowed to draw 100mA; this works fine for charging flashlights and powering other USB-format novelty items. Also, this is juust about what an average smart phone consumes at idle (that is to say I don't know the exact values of the Droid explicitly) -- so this would explain why a charger would be able to sustain, but not charge, a phone plugged into a dumb USB port.

I say 'dumb' for a reason --this is the point of my post-- because the connected device must communicate with the host in order to obtain more than the minimum allowance (up to between 900 and 1500mA depending on port type).
The kingpin here is that 'smart' devices err on the side of caution: they refuse to draw more than the minimum allowance unless they can obtain confirmation to draw more. So you need a charger that is 'smart' enough to not only spew 5V, but also to respond to requests from more cautious devices.

Sadly, this distinction is rarely made on ebay auctions, so you'd need to buy typically more expensive retail chargers and/or experiment with different models...