Current Pulsing Keeps Power Bank Active

Introduction: Current Pulsing Keeps Power Bank Active

About: I am a retired Electronic Systems Engineer now pursuing my hobbies full time. I share what I do especially with the world wide student community.

Using Mobile Power Banks to Power Electronic Circuits

Mobile Power Banks can be used as an excellent power source for simple electronic circuits and DIY projects. However, as they are designed primarily for charging mobile phones they possess certain inbuilt features which need to be suppressed.

Basically the power bank shuts down if the output current drops below a set threshold. To do this the internal circuitry continuously polls the output current over a period of 12-15 seconds and shuts down if the value is below a threshold.

A simple way to overcome this would be to have a bleeder resistor continuously connected across the power bank output. This is very inefficient and would cause unnecessary power drain.

Based on experiments carried out on two power banks and the references cited below I present a simple circuit which needs to be inserted between the power bank and our experimental circuits. This circuit generates a pulsed current load of 150 mA for approximately one second every 10 seconds. This satisfies the sensing requirements of the circuitry within the power bank while effectively reducing the power drain to one tenth as compared to that of an equivalent bleeder resistor.

References:

1 TI application note: Port Detection for Power Banks

http://www.ti.com/lit/an/slva770/slva770.pdf

"To extend battery life and minimize power when a power bank is powered off during system idle, shipping, or storage, the power bank can turn off the discharge path of the battery so that the output voltage is zero to minimize the battery leakage current. Once the power bank is signaled to be charged or discharged, it wakes up the system from idle mode and re-enables the discharge path; several methods are implemented to detect the input and output attachment events."

2. Forum discussions: USB Battery Bank Prevent Shut Down

https://forum.pjrc.com/threads/28624-USB-Battery-B...

Step 1: Circuit Description & Experimental Verification

Based on NE555 Timer IC

The circuit is based on the popular NE555 timer IC which has been setup as an 'Astable Multivibrator'. Capacitor C2 is charges through R1+R2 and discharged through R2. The waveform at the capacitor is shown in blue in the oscilloscope trace. The square wave output of the NE555 at Pin 3 is fed to a PNP transistor to drive the 22 Ohm load (R4). The PNP transistor collector waveform is shown in red. A LED in parallel blinks whenever the PNP transistor is on and a pulsed current flows through R4.

Experimental Verification

I rigged up the circuit and checked it out on a bread board and tried out this scheme with two power banks.

The EVEREADY power bank needs to be switched on for it to start and has a dwell time of approximately 15 seconds before it switches off in case the output current is below the threshold value.

The ivoler power bank comes on automatically when the circuit is connected based on even a small current being drawn. The dwell time is approximately 12 seconds.

I found that the power banks remain ON at an approximate threshold current of 100 mA and have selected a safe pulse current of >150 mA. With a 1:10 duty cycle this is equivalent to a 15 mA continuous load.

My test circuit

I have used this scheme to power a PIC microcontroller which with associated components draws approximately 50 mA and the power banks were shutting down with this load after 12-15 seconds.

Other power banks

Other power banks may need minor changes in the circuit in terms of the current pulse magnitude, duration and repetition rate. The Ne555 based circuit has been chosen as it can easily be modified to cater to a large spread in values.

Step 2: Boxed

I have put the circuit into a small plastic container and wired a USB-A to USB-A cable. This is now a handy device which I can use with any power bank powering my experimental projects.

2 People Made This Project!

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5 Comments

0
pgs070947
pgs070947

7 months ago on Step 1

Very interesting.
I am working with Belkin Pocket Power units and trying to power a remote gas meter sensor with XBee radio.
I thought it would be dead easy but no way.
The first thing I found was that it turned off after about 19.5 minutes. Once it had started putting out 5.1volts, the Belkin LEDs turned off, the power would continue until the 19.5 minutes were up.
The next thing I found was that it needed about 100-mA to keep it alive by dabbing a 50-R resistor across GRD and 5-volts for about 1-second kept the process going.
The problem is that you need to start the Belkin putting out power in the first place.
You can use the power button on the Belkin.
I also found that just plugging in the USB with all five (shield, ground, 5-V, white data, grey data) leads totally disconnected at the load end (I had removed the the second plug from the USB cable and separated the core leads and shield).
The physical act of plugging in was enough to start things.
I know that the data lines can have a resistor network to tell the load, say a phone, that the cable is power only, but simulating that at the load end did nothing.
When the Belkin goes dead, that's it. You need to start it with the button or plugging the USB in, even if nothing is connected.
The Belkin USB sockets look quite normal, no switcking contact like a stereo plug.
I went over it with a powerful magnet, nothing.
I'm mystified. There's more to these things than meets the eye.
The only thing that works is the periodic 100-mA load, so I will be giving the timer circuit a go.
The long time delay might be a problem so I might try one of Texas (Linear Technology) Timeblox timers.
I'll report back if it works.
Thanks for posting

0
Ajaxjones
Ajaxjones

9 months ago

Interesting read , i am having the same problems with trying to power a small Wemos. It doesnt have enough power to get the power to turn on, but what I have discovered with the power bank I have is that placing a small magnet on it in certain positions will power it up! I am not quite sure what is going on, possibly induction? but it powers up and all the lights and the bank springs to life and lets the Wemos run. If you keep the magnet there, then It doesnt seem to go off either and the power level lights of the power bank stays on.

battery on power bank.jpg
0
wozlaser
wozlaser

10 months ago

this circuit saved the day for me, first try. I used a 2n3906 for the transistor. also I went electrolytic with the .1uf capacitor, negative toward ground of course. any ol LED works too.

0
master_clinician
master_clinician

1 year ago

Thank you Ajoy. I tried several other approaches before reading your article. Yours was the first approach that worked consistently. Thanks for sharing your incredibly useful circuit and observations.

0
straif69
straif69

Question 1 year ago

hello, what can i modify to gain more amps in pulse ? maybe change some resistor with trimmer ? thank you