USB Load to Stop Power Banks From Auto Shutting Off
by f5AFfMhv in Circuits > Electronics
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USB Load to Stop Power Banks From Auto Shutting Off
![IMG_20200620_215637.jpg](/proxy/?url=https://content.instructables.com/FR8/T169/KBNNM47H/FR8T169KBNNM47H.jpg&filename=IMG_20200620_215637.jpg)
![IMG_20200620_215626.jpg](/proxy/?url=https://content.instructables.com/FCZ/9DV5/KBNNM47I/FCZ9DV5KBNNM47I.jpg&filename=IMG_20200620_215626.jpg)
I have several power banks, which works great, but I encountered issue when charging wirelesses earphones power bank will automatically shutdown, because of too small charging current.
So I decided to make USB adapter with small load to keep power bank from shutting down when I'm charging my earphones.
Supplies
- Prototyping board
- USB type A connector and socket
- Resistors
- Hot glue gun
- Soldering equipment
Determine Power Bank Shutdown Current
First we will need to figure out what minimal current is needed to prevent power bank from shutting down:
- You can use USB meter (like these) and variable load (like this).
- You can solder potentiometer to USB type A connector power pins and use multi meter in series to determine the shutdown current.
- Easiest way is just guess, 50 mA load probably will do the job.
I used first method and determined, that my power bank shuts down if load is less than 40 mA.
Calculating Resistor Values
![Screenshot_2020-06-20_23-49-35.png](/proxy/?url=https://content.instructables.com/FJX/3BFB/KBNNMA0P/FJX3BFBKBNNMA0P.png&filename=Screenshot_2020-06-20_23-49-35.png)
Purely for aesthetics I decided to add LED. 40 mA for LED is to much, so I will drive it with 10 mA and 30 mA will dissipate in parallel resistor.
So we know that
- U = 5 V
- U_led = 2 V for blue LED (LED drop voltage you can determine with multi meter in diode testing mode)
- I_led = 10 mA
- I_r = 30 mA
Than
R_led = (U - U_led) / I_led = 300 Ohm (use common 330 Ohm resistor value)
R = U / I_r = 167 Ohm (use common 150 Ohm resistor value)
Assembly
![IMG_20200616_231224.jpg](/proxy/?url=https://content.instructables.com/FU3/82EF/KBNNM47P/FU382EFKBNNM47P.jpg&filename=IMG_20200616_231224.jpg)
![IMG_20200616_231241.jpg](/proxy/?url=https://content.instructables.com/F1K/KKLH/KBNNM47M/F1KKKLHKBNNM47M.jpg&filename=IMG_20200616_231241.jpg)
![IMG_20200616_231255.jpg](/proxy/?url=https://content.instructables.com/F5F/IVCH/KBNNM47L/F5FIVCHKBNNM47L.jpg&filename=IMG_20200616_231255.jpg)
I cut approximate size of prototype board and than sanded edges with fine sandpaper.
Soldering is straight forward, just be careful not to mix up USB connectors power pins.
I made case from hot glue, just forming it into square shape with flat object and finishing it by sanding.
Testing
![IMG_20200620_173840.jpg](/proxy/?url=https://content.instructables.com/FX0/XWHA/KBNNM47J/FX0XWHAKBNNM47J.jpg&filename=IMG_20200620_173840.jpg)
![IMG_20200620_173721.jpg](/proxy/?url=https://content.instructables.com/F21/T9P3/KBNNM47K/F21T9P3KBNNM47K.jpg&filename=IMG_20200620_173721.jpg)
Load works as designed and now I can fully charge my earphones :)