I have a car adapter with 2 USB ports, 1 of the devices is a continuos recording camera (with an SD card in it) and the other device is my Android phone (Sony Xperia, Android 4.3). However, when I connect both devices to the adapter the continuos recording camera stops recording and shows 'external storage' on the screen, and there is no way to stop this behavior on this device. In my Android device I can see no messages, but can indeed see the other device's SD card. There are no popups in Android when I connect to it. Is there any way to stop Android from detecting this other device?
Use a needle or a pair of needle-nose pliers to break the data pins on your adapter, so they won't connect to the device. Breaking the data pins doesn't inhibit the adapter's ability to supply voltage across the power pins. Alternatively, it might be easier to cover them with a small piece of insulating tape; the easiest way to do it will depend on the shape of the adapter and what tools you have to hand.
Of the four pins inside a USB plug/socket, the middle two are the ones you want to cut off or cover. Be careful not to damage or cover the two outer pins. It should go without saying that you should do this while the adapter is not connected to anything.