Yesterday I bought cheap iWalk branded power bank to make my Ingress (read – working out) sessions last longer and to my dismay this power bank did not charge my phone while I played Ingress. Since not so long ago I developed this universal USB charger, I am well aware that at large charging currents (1A and more) there is quite a bit of a voltage drop in USB cable and at least modern Samsung phones sense this drop and reduce charging current. I cracked open iWalk and no surprise there, output at USB connector on bank side was 5.06V. Solution to this problem is to bring up output voltage to about 5.2V, which is still within USB specifications, but compensates for the voltage drop caused by thin USB cables.
Luckily iWalk used two easily identifiable adjustable switching step-up converters with resistor voltage divider feedback network, so all it takes to fix the issue, is to replace those resistors with new ones and see if that helps.
Stay tuned while Farnell delivers my resistors, once that happens, I promise to write a new blog post with some images.
Update – apparently that post I promised is not going to happen because there is something fishy going on with that power bank and I do not have time and/or will to figure what exactly.