ESP32 power supply

The Heltec folks certainly didn’t go overboard in documenting their WiFi Kit32, and even the pinouts, and pin names seem to change over time. I have one of these hooked up to a 5 v. supply, attached through the 5 v. pin on the board, and it works. But when I hook up the USB cable to program it, the 5v. supply drops instantly to about 4.6 v., which I’m sure means sudden high current draw. Since that is what makes it happen, it’s not something like sudden large current draw due to WiFi actions. I would guess it’s some sort of battle between the external 5 v., and the 5v. coming in via USB. Has anyone else had this problem?

Thanks in advance for any information shedding light on this. I don’t think I’d try using the Heltec board in any actual product.


Maybe there is a diode in the circuit, so the 5V from the USB is not directly connected to the 5V pin .................

If your sure the drop in voltage is caused by a high current draw, what current did you actually measure as 'high' ?

The only way I can make sense of what you describe is if the USB connection is actually at 4V6 and is drawing current from the 5V supply, brining it down to 4V6. Maybe that is or isn't the answer, but it's the only thing I can think of. I take it the 5V supply can't supply much current, is that correct? Where are you measuring?

I have 4 WiFi kit 8s, which are the ESP8266 ones with a display. I think they are brilliant, but you are right about the documentation being crap.

If one was to look at a ESP32 DevKit WROVER or WROOM schematic one would see that the 5V from the USB line is directly connected to the 5V of an external power supply.

If something were to happen to the 5V external p/s, that something happening is directly passed onto the connected USB line. I use a powered USB hub between the computer and the ESP32.


When, I did a FUBAR and caused the external p/s to do a bad thing, the bad thing was fed directly into my laptop, and bye-bye laptop. Thus, I found out that a powered USB hub costs way less than a new laptop.

Also, since using a powered USB hub, I’ve not had to press the button to make an ESP32 take a upload.

To respond to two questions in two different replies, I do use a powered USB hub for all peripherals, and my 5v. supply is a heat sinked 7805 and a 470 uF cap. If the esp32 draws 250 ma. (the apparent max for internet activity), the 7805 would be dissipating 2.5 W


If the esp32 draws 250 ma.

If ?

What is the actual measured current draw ?

A lot of time has passed since I started this thread, but just to wrap it up, I found a simple solution. If you have an independent power supply for the Heltec board, then make a data only USB cable. Just slice the cable insulation, isolate the red wire (Vcc), and cut it. tape up the slice, being careful that the ends of the red wire don’t contact the shielding (if any), and Voila!, no more dueling power supplies.