I am trying to run an Arduino Uno R3 from an EnerPlex Jumpr Prime 4400mAh power bank. It is designed as a cell phone charger, does not have an "always on" feature, and consequently turns itself off with the low power draws of the Arduino.
There are well documented threads about this problem with usb chargers/batteries and the solution has been to pulse intermittent high current through an external resistive load to trick the charger into thinking it should stay on. Most postings indicate that one to five percent duty cycle of switching 5v over 22 ohms does the job.
I have implemented this solution with an npn transistor switched on/off from a digital output pin, low side switching 5v across a 22 ohm resistor. I have confirmed that constant current across the 22 ohm is enough to keep the charger turned on. My pulse circuit is working but I can not achieve lower than a 50% duty cycle to keep the charger turned on. I have tried longer and shorter pulses, higher currents, and other variations of the duty cycle with no success in getting to the 5% or less that others have achieved..
Does anyone have any recommendations, or is my charger too smart, or dumb, to be fooled.