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A lot of these charger/powerpacks have charge negotiation logic, to determine the maximum current it should deliver to the device. It is possible that your unit is falling back to a 'safe' level and limiting the current to your device. Usually this can be fixed by placing the proper load/divider on the USB D+/D- lines or via the 'ID' pin of micro USB connectors. This device appear as if the default current delivery is set at 500mA (micro USB).
Thanks Gene. Good observation on the micro USB where I failed to do the simple math.
I am putting together a Raspberry Pi Model B that will be dedicated to running OpenCPN software to track AIS messages from ships and display it on an official 7" Raspberry Pi LCD screen. It will have a low power AIS receiver and eventually GPS receiver which I envision being powered from a rechargeable battery over USB. I have AIS working but haven't hooked up GPS yet - see the photo below:
The battery shown must be drooping and the "lightning" symbol is showing. When completed the project is expected to run with the screen off (screen saver mode) much of the time and I see about 0.4 A from a wall power supply in that state. When the screen is on I measure about 0.8 A from a wall supply. I am looking for a reasonably compact solution that is easy to implement. The desirable battery life would be 4 hours on (or 8 hours with the screen off). Theoretically the battery in the photo will give about half that so that is the floor. I want to put it in a portable enclosure for protection but it won't be rained or splashed on and ideally the battery will be inside the enclosure but that is not a show stopper. The antenna will be connected to the side of the case via the connector in the photo.
Here are my questions:
- Any ideas for an off the shelf battery or easily hacked supply for 5V over USB and the requirements outlined above?
- Any ideas for an enclosure?
- Ideas for reduction power also appreciated
Oh, and I should add low cost. An industrial look or plastic for the case is fine. This is for demonstration and is not safety critical. I have reasonable skills for modifying a case or hacking a power supply. If all else fails I will build a wooden case and use the battery shown but would like something a little more polished. Any ideas appreciated.