Sometimes my Iphone will not charge when i connect

If your iPhone is not charging when you plug it into a wall charger or into you computer's usb port, this is a usb connectivity issue and the connection just needs to be reset. All that needs to be done is plug the iPhone's cable into the phone but don't plug into the computer yet. Hold the phone's select button (the round button with the square) down for about 30 seconds or until the apple appears on the screen. your phone will reload and reset the connection and the computer should recognize the device. Allow the phone to charge for at least 30 minutes before unplugging.

The easiest way to charge an iPhone is to plug it into the USB port of a computer or some wall chargers may not supply exactly +5v which the iphone requires. because the iPhone doesn't charge like other normal USB devices. Just by supplying 5 volts to the USB cable of the iPhone will not charge it. That's why most wall chargers will not work with the iPhone.