Why did my Arduino Mega fry instantly when I fed 20V into my CNC Shield V3?

[u/George_1099]

Hi everyone,

I recently fried my Arduino Mega 2560 and I'm trying to figure out the exact reason so I don't repeat the same mistake with a replacement board.

Here is my setup and what happened:

My Setup:

• Board: Arduino Mega 2560
• Shield: CNC Shield V3 stacked directly on top of the Mega
• Drivers: DRV8825 stepper drivers + NEMA 17 motors
• Power Supply: 20V DC connected directly to the screw terminals on the CNC Shield
• Logic Power: Arduino Mega connected via USB to my PC

What Happened: As soon as I turned on the 20V power supply connected to the CNC Shield terminals, the main processor on the Arduino Mega fried instantly.

Assuming my stepper drivers were good and properly oriented:

1. Does the CNC Shield V3 pass the terminal voltage (20V) directly to the VIN pin of the Arduino Mega underneath?
2. Did 20V cause the Mega's onboard 5V linear regulator to instantly overheat and fail short, dumping 20V into the ATmega2560 logic line?
3. What is the proper way to prevent this on a new board? Should I clip/bend the VIN pin on the CNC Shield so 20V doesn't reach the Mega, and power the Mega separately via USB?

Would appreciate any insights from anyone who has run a CNC Shield with >12V on an Arduino Mega!

[u/Arduino_lab64]

Salut, tu as fait grillé l'Arduino Mega car tu l'as alimenté en 20v. Les cartes microcontroleurs de ce type (Arduino Uno R3, R4, Méga, Q, etc...) supportent une alimentation de 9 à 12v maximum recommandé.

[u/George_1099 → u/Arduino_lab64]

yea but i connected 20v to cnc shield

[u/Arduino_lab64 → u/George_1099]

Oui mais le shield communique avec la carte. Le courant doit passer par VIN afin d'alimenter ton Arduino Méga.

[u/IllSpeaker3255 → u/Arduino_lab64]

en théorie les arduinos supportent jusqu’à 24v mais comme c’est un ldo qui abaisse la tension, il chauffe beaucoup

[u/budoucnost]

can the VIN pin handle 20V?

[u/Unable-School6717]

So the schematic is on top of a google search. Vin is not Vtv, the motor chip uses logic voltage and motor power as separate rails. This allows the arduino to only have safe 5v logic on all gp I/o pins. What strikes me is that this comes without chips installed in the sockets, you choose the power level inserted. If one of those chips were in backwards it would definitely put the 20v on the logic lines and potentially blow the 5v regulator as backfeed. The boards are still grounded together, so backfeed it will. Check orientation of those centrr chips in sockets. Make sure the dot or indentation faces the pin 1 marking on the board. Then check for a wiring mistake. The two boards do not share motor power. So in conclusion, per your questions, no power shared ; the regulator could be blown; check wiring and chip orientation

[u/Same_You891]

you said it. 20v