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I have a 3A fan hooked up to an ATX power supply in parallel with a transformer which powers my board through VIN/GND.

The ATX is gated by a relay on its DC side and seems to cause enough of a current drain that it causes the Arduino to reset.

I have place a 470μF capacitor accross the Arduinos VIN and GND pins and it seems to have stopped the problem, but I'm not too experienced using capacitors. Is this an apropriate value? I'm not sure what difference it would make. And is this a wise move as I so think?

Standard?

EDIT: Here's a very basic sketch..

12V Transformer powers arduino on VIN/GND pins, other pins a 5V, GND and control for relay

12V Transformer powers arduino on VIN/GND pins, other pins are 5V, GND and control for relay

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    If you directly drive the relay from an Arduino pin (as it seems on the provided drawing), then you should probably consider using a transistor (or a MOSFET) to drive it. Finally, don't forget to use a flyback diode to avoid ruining your Arduino because of high flyback voltage. – jfpoilpret May 6 '16 at 6:36
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I have a 3A fan hooked up to an ATX power supply in parallel with a transformer which powers my board through VIN/GND.

I don't entirely follow that wording. Please draw a picture.

I have place a 470μF capacitor accross the Arduinos VIN and GND pins and it seems to have stopped the problem, but I'm not too experienced using capacitors. Is this an apropriate value? I'm not sure what difference it would make. And is this a wise move as I so think?

470µF is fine. In this situation the bigger the better. If 470µF fixes it then 470µF is fine. Don't be afraid of going higher though. I have 3,300µF capacitors here that are commonly used for similar purposes.

What you have implemented is called a reservoir capacitor and is a common use for large value capacitors like that.

  • Perfect..That makes sense. Thanks. reservoir eh! Hope the drawing makes the first statement clearer. – xeuari May 5 '16 at 21:50

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