Introduction: USB Load to Stop Power Banks From Auto Shutting Off
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.
- Prototyping board
- USB type A connector and socket
- 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:
- 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 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
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 :)