[Epic 4G Accessories] IBNobody:
This message is a summary of my previous messages. I hope that it will be useful. I wrote this to document what I found out about the Epic. I'm cheap, and I didn't want to buy ANOTHER charger for my car. I had a 3A, 2-port USB charger, and I was mad that my Epic was charging slowly. I managed to modify my charger to get it to perform just like the wall charger that came with my phone.

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Q: How much current does the Epic draw from a normal (bus-powered) USB port when charging?

A: 380mA.

Q: How much current does the Epic draw from the OEM 700mA wall charger when charging?

A: 600mA

Q: How much current does the Epic draw from a car charger or an aftermarket wall charger?

A: It depends...

If the charger has the two data pins (D+ and D-) shorted, the Epic will attempt to draw 600mA. Otherwise, it will draw 380mA.

Q: How can I tell if my phone is charging at 380mA or 600mA?

A: Turn off USB debugging (Home Screen\Settings\Applications\Development\USB debugging).

If you plug into a 380mA source (D+ and D- not shorted), you get a "Charging/Mass Storage/Tethered Mode" popup when you unlock your phone.

If you plug into a 600mA source (D+ and D- shorted), you do not get a popup.

Q: I have a 1A micro USB charger from another phone. Can I use it to charge the Epic?

A: Yes, but you won't get it to charge any faster than the 700mA OEM wall charger. The phone will only draw 600mA at most, regardless of how many amps the charger can supply. (And that assumes that D+ and D- are shorted.)

Q: I have a Palm Pre wall charger. I've heard that it charges the phone faster than the Epic wall charger. Is this true?

A: No. The Palm Pre wall charger does not charge the phone any faster than normal. With my phone hooked up, I measured 590mA (600mA with cable loss). I also saw that the charger had D+ and D- shorted. It behaves exactly like the Epic's charger.

Q: Will these 1A chargers damage my phone?

A: As long as the charger is able to supply the necessary current without overheating, chargers from other phones will not damage the Epic. A charger may be rated for 3A, but the Epic controls how much current it draws.

If you buy a cheap charger, you run the risk of having the charger's chip burn up. Among other things, this could short the charger's input voltage (12V from a car) to the USB V+ line and fry your phone.

Q: I have a USB charger that seems to charge my phone slooooowly. What can I do?

A: Your charger is probably supplying 380mA (or worse). You have a few options:

NOTE: Before doing any of this, make sure that your charger is rated at 700mA or greater. If you have an unmarked charger, chances are that it will not be able to supply 700mA out of the box. Many car charger (such as those for the Nintendo DS) have built-in current limiters that prevent the device from drawing too much current.

1.

Modify Your Charger:

Open up the charger and look to see if D+ and D- are shorted. (They are the two middle pins on the standard size USB plug.) Modify your charger so that it shorts D+ and D-, and remove any pull-up or pull-down resistors that connect D+ and/or D- to power or ground.

2.

Modify A Cable:

Slice open a spare micro USB cable (or the cable from your charger), being careful not to damage the red or black wires. Cut the green and white wires (D+ and D-). Strip off a little bit of the insulation from the green and white wires that lead to the micro USB connector. Twist these wires together and wrap in electrical tape.

NOTE: This will prevent the cable from being used as a USB data transfer cable.

3.

Buy a USB Charging Cable:

Look for a special USB charging cable that already has D+ and D- shorted.

Q: If I buy or make a charging cable, can I get 600mA from a normal (bus-powered) USB port?

A: It depends. The USB spec says that a port can only supply 500mA max. There is usually an overcurrent monitor built into the port that will prevent an overcurrent condition. The OS will pop up a message telling you that you've exceeded the current sourcing capacity of the port.

There are some laptops, however that have ports that allow you to violate the USB spec and draw up to 1A from a port.

Use caution when experimenting.

Q: Can you tell how much current the device draws from the device?

A: No. You CAN, however, get a battery graphing app like Battery Graph.

http://www.appbrain.com/app/battery-...odroid.battery

If you set the monitoring interval to 1 minute and start charging your phone (which should be low on charge) with the wall charger, you'll see a battery curve. You can then repeat this process with your alternate charging method. If you compare the slopes of the charging curves, you'll be able to tell if your alternate charging method is performing the same as your wall charger.

It's not as quick as using a DMM, but it works. It's how I initially saw I was having a problem.

Q: How can you tell if your USB cable has D+/D- shorted?

A: 99% of all cables will not have the lines shorted. You have to buy a "charging cable". But if you are in doubt as to what cable is what, plug it into a PC's USB port. Either the PC will detect the device (not shorted), or you'll trip the USB port's overcurrent mode (shorted).

Or... You can buy a DMM and check the resistance between D+ and D-.

- N