I have been powering my WeMos D1 R1 and D1 R2 Arduinos (with ESP8266) using a simple USB cable connected to a standard charger whose rating is 3.1 amps. Is this sufficient to charge two such Arduino boards (it has two USB slots) simultaneously?

Also, should I be using the other Power Input which I understand is 9V?

All the specs I have seen specify the voltage but not the current usage.

Either way, what is the maximum amperage that the board might need/is rated for? Is it different for the R1 vs. R2? Is it possible to measure how much it is using from any of the pins?

  • an USB 2 port gives max 500 mA. so 3.1 A should be more than enough.
    – Juraj
    Jun 11, 2023 at 13:05
  • 1
    You can use a USB meter like this.
    – Fahad
    Jun 12, 2023 at 10:52

1 Answer 1


It is possible to measure how much it is using from any of the pins?

Put an ammeter (multimeter in current mode) in series with the power supply and measure it, when configured in the way you intend to use it.

  • Good suggestion, but it will be hard to do without splicing the USB cable. Now this becomes a project! :-) If I were to do that, which would be the right wire to put the multimeter on?
    – Chiwda
    Jun 11, 2023 at 13:00
  • 1
    Just about every USB wire I've cut into contain a red (+5V) black (ground) and green & white (data). You can cut either the black or red wire in such a cable and insert an amp meter. Note, always try the high Amp meter first! When you are confident you can not read a current because it is too small, then switch to the mA meter configuration. That said, there are many Common Off The Shelf (COTS) USB devices that measure Amperage.
    – st2000
    Jun 11, 2023 at 13:55
  • I will do that. Meanwhile, is there any place a maximum rating is specified?
    – Chiwda
    Jun 11, 2023 at 15:18
  • 1
    I believe USB 2.0's maximum is 500mA. Other USB definitions exist. Later versions of USB exist. Some companies have done odd things to detect and support higher current capabilities. And then there is negotiations between the USB peripheral and USB host. You are going to have to do some digging for your specific situation.
    – st2000
    Jun 11, 2023 at 16:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.