Introduction: USB Load to Stop Power Banks From Auto Shutting Off

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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

Step 1: Determine Power Bank Shutdown Current

First we will need to figure out what minimal current is needed to prevent power bank from shutting down:

  1. You can use USB meter (like these) and variable load (like this).
  2. You can solder potentiometer to USB type A connector power pins and use multi meter in series to determine the shutdown current.
  3. Easiest way is just guess, 50 mA loadprobably will do the job.

I used first method and determined, that my power bank shuts down if load is less than 40 mA.

Step 2: Calculating Resistor Values

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)

Step 3: Assembly

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.

Step 4: Testing

Load works as designed and now I can fully charge my earphones :)