How much current can I draw through the USB port and out the 5v pin?



  • Is there any power regulation I should be aware of or can I safely pull as much current as my USB charger can deliver, through the USB port and out of the 5V pin?

    Many thanks!



  • Hi,
    looking at the schematics of the D1 mini pro on wemos.cc website,
    here
    there is only a B5819 barrier diode between the connector and the pin.
    Googling the datasheet of this diode, the typical forward current is 1A (below 55°C).
    My understanding is that below this value you're safe.
    I didn't check the other boards but you can easily do the same on your own.



  • Hello @excession ,

    interesting to see that always the same questions come up again. Unfortunately the old forum is lost.

    Basically yes, however ! You haven't mentioned which board you are using.

    On the Wemos D1 R2 is a 0.5A fuse between the USB connector and the USBVCC.
    On the Wemos D1 mini and the D1 mini pro is a diode B5819 between VBUS and +5V. This could the limiting factor.

    You also need to check the layout of the PCB. If the traces are to small, means to narrow, they might not be able to withstand the current and will probably burn.

    The current answer should be: it depends, but you shouldn't. If you need high current, try another approach, e.g. by-pass the board. But be careful not to generate a back-current or short cut.

    What is your intended use?
    7th Dwarf



  • Hi Folks, thank you both for the speedy replies and apologies for not mentioning the board I'm using (annoying I know).
    I read on the forum sticky how you've recently lost your back catalog of content, that must be incredibly frustrating.

    I'm using a D1 Mini, V2 to drive a pair of these LED matrix boards.

    I'd like to minimize the the number of holes in my enclosure (I'm aiming to make it look like a simple block of wood as much as possible, the LED matrix and the rest of the pine enclosure are going to be covered in veneer.) I'd like to retain access to the USB port even though I'm using OTA for firmware uploads. So ideally I want to run this from a 1A USB charger.

    When running, the peak draw I've seen (with all LED's lit on full brightness) has been around 600ma. From @karlo_65's description it sounds like I should be within the tolerance of the barrier diode?

    For interest; I've included a couple of pics of the project thus far. The green PCB on the breadboard is an RCWL-0516 microwave presence detector. This turned out to be a great little module capable of detecting motion right through the LED matrix!

    (Apparently I can't upload images, only PDFs... so, img hosted on tinypic.com)
    (And apparently I need to wait 10 hours to respond to you! Wish I'd known that before getting into a reply. Sigh.)

    alt text

    http://tinypic.com/view.php?pic=16m6lit&s=9



  • In the worst case you can always remove the diode and short the pads with a blob of solder. As long as you don't plan to power the board from the 5V pin while at the same time programming it through USB, you should be fine.



  • @deshipu said in How much current can I draw through the USB port and out the 5v pin?:

    In the worst case you can always remove the diode and short the pads with a blob of solder. As long as you don't plan to power the board from the 5V pin while at the same time programming it through USB, you should be fine.

    Good idea, thanks :)



  • I've had the same question! I'm going to be using an array of 4 of these 8x8 led matrix displays. From what I read each of them theoretically has as max current draw of 320ma. I was wondering if I can power the displays straight from the 5v pin (assuming that I use a 2A usb power adapter)? I'm using a Wemos D1 mini. Cool project by the way @excession!



  • @marcvon

    The built-in regulator on the WeMos module can't handle that much current.

    When powering a bunch of displays, you'll likely use a power source with the display's preferred voltage, that can provide sufficient current, e.g. 5V, 1A or 5V 2A etc., to drive the whole project.

    Then, connect both the displays and the D1 Mini's Vin pin to the 5V power supply (perhaps with a filter capacitor). The D1 Mini has a voltage regulator which will step it down to 3.3V. You might need level shifters to communicate with the LED drivers, but they may also work fine with 3.3 signals. (There should be no 5V signals going back to the WeMos module.)



  • @Roo-ster The built-in regulator is not involved when you draw current from the 5V pin, and that's what we have been talking about here.



  • Cheers @marcvon, looks like the barrier diode is happy enough to pass at least 800ma; my signs been working happily for a couple of days that way.


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