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Topic: Powering NodeMCU V3 - what I do wrong? (Read 750 times) previous topic - next topic

XnIcRaM

Dec 06, 2017, 12:22 am Last Edit: Dec 06, 2017, 10:10 pm by XnIcRaM
I have trouble with powering NodeMCU V3. I found here and not only there than max voltage on Vin pin is 20V. I connect Li-Ion 14,4V accu as Power Supply for my NodeMCU board, but when I connect + from acc to Vin pin then one of diode exploded immediately. I post here photo of my NodeMCU board, diode which was exploded is SMD 1N5819. Voltage regulator on my board is AMS1117-3.3. Now board work but only when I power it up through USB or directly to 3.3V pin (ofcourse with 3.3V) because board work on USB power only then I think that AMS1117-3.3 isn't broken, only diode has beed burned, but the question is WHY?

BTW: my Li-Ion acc 14.4V when I connect it to nodeMcu board have 16.6V and theoretically it's beed 1V over max AMS1117 input voltage but why diode explode and not the voltage regulator?



justjohn

Maybe because the diode (1A) couldn't handle as much current as the AMS1117 (1.5A) so it blew up, keeping the AMS1117 from doing so. With a stronger diode, the AMS1117 may have blown up instead.

XnIcRaM

maybe... but nodeMCU doesn't need even 500mA

justjohn

It's my guess the excess voltage caused the AMS1117 to conduct and short to ground with as much current as the battery was able to provide which blew up the diode. It had nothing to do with current requirements of the nodeMCU. In other words, if the AMS1117 was connected to just a resistor and LED with the diode in the same place, the same thing would have likely happened. Maybe create such a circuit and test just to find out. Likely the same thing if "only" the diode and AMS1117. I'm more of a programmer than hardware guy though, so maybe someone with more of that knowledge will see this and give a comment.

MrMark

"diode which was exploded is SMD 1N1519"

Is this correct?  1N1519 is a 4.7 V Zener diode.  The part is there to prevent back feeding VddUSB with Vdd5V, but if you put 14.4V on Vdd5V and the USB is connected, you'll exceed the Zener voltage with no current limiting and it will fail.

The photo shows 1N5819 which is a Schottky diode and would make more sense in this application.

Perhaps your board was built with the incorrect part?  I have a Lolin NodeMCU V3 board at hand and it has "S4" Schottky diodes in that position.

justjohn

"diode which was exploded is SMD 1N1519"
I saw 1N5819 (schottky) on his drawing, but you're right that he mentions 1N1519 in his text.

XnIcRaM

There is mistake (which I already correct) this diode is ofcourse 1N5819 (schottky)

MrMark

Can you tell the orientation of the blown diode?  On my board it is mounted in the opposite direction as the one next to it, that is, the white bar is the side nearest the circuit board edge.  You photo appears to have a white bar on the other side, but it might just be the lighting.

XnIcRaM


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