USB Portable Charger Problem

[c00kie]

Hi Everyone,

I am guessing this is where I would post this, but if I am on the wrong forum, I apologize. I am in the process of making a portable raspberry pi emulator station within a small 10x7 inch case. I did some research, and ended up purchasing the following for the screen, battery, and step up voltage regulator -
http://www.amazon.com/gp/product/B008FLE7PA/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1
http://www.amazon.com/gp/product/B00JM59JPG/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1
http://www.amazon.com/gp/product/B00C17FS52/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1

I have the emulator up and running, and the screen looks great. The screen needs ~8 volts to operate, so it won't work on a standard USB. The voltage regulator works on a standard USB port with the screen attached, however, when I connect it to the USB power brick, the supply immediately turns off. I have tried both the 2.1 and 1 AMP ports, and tried to tweek the voltage regulator, but I get the same result. The Pi works fine on the brick when it is by itself, but I can't get the USB with the regulator/screen attached to work with the brick.

Could there be some kind of safety feature on these USB power bricks that detects a change in voltage and cuts the power? I'll be really bummed if I have to run this off of power, since it will be portable.

Hopefully my explanation made sense. I can send pictures later if that helps.

 

[Pylon]

Can you post your wiring scheme? Might be something going on with ground loops.

 

[C101]

Please try plugging only the boost converter into the USB power brick with no load attached. You can use a multimeter to check the output voltage to see if the system is functional.

Doing this, we can check to see if the problem is caused by the inrush current from the USB supply to the boost converter. I can see that the boost converter has ~440uF of capacitance on the input, and the USB supply may hit it's over-current or under-voltage thresholds if a "hot-plug" is performed.

We also know that your wiring is good, because when you plug it into the PC power supply (Via the USB ports), the circuit works as designed. This is the other factor that makes me believe that it may be an inrush current issue, as the PC supply is going to be more robust in a hot-plug event.

Another alternative to try is to use an old-school transformer based USB power supply, instead of a more modern switching type which you likely have. These are much simpler, and as a result, possibly more robust to brief current surges on the output.

Unfortunately, there is not a whole lot we can do to help you beyond guiding you through simple troubleshooting steps, if it turns out to be more complicated, better test equipment may be needed, such as an oscilloscope.