For the purpose of a project I wish to power an arduino using a supercapacitor charged to 5V. The supercapacitor will be fed straight into the power Vin and GND terminals on the Arduino. No power plug or USB connected to a computer will be connected, so all power is to be drawn from the supercapacitor. Previously I have powered the board using a 0-12V variable voltage supply, and the arduino draws between 20 and 35 milliamps.
My question is this, if I connect the supercapacitor straight to the arduino board, will the arduino govern how much current to draw from the supercapacitor? Or will I need to place a resistor in series with the supercapacitor discharging in order to regulate current and stop the supercapacitor rapidly discharging and frying the board?
Lastly is this feasible at all? I am aware that as the 5V from the supercapacitor will drop off the period during which the arduino will run is limited.
Any advice is appreciated as I do not wish to fry my Arduino board attempting this.
Best Answer
The voltage on a capacitor is proportional to the charge stored in it.
That means that as the device draws current, the voltage will drop. You have to decide how low is acceptable. Do the math.
For example, let's say the device can still run from 4.5 V. That means the capacitor voltage can drop 500 mV before the system doesn't work anymore. Let's use a 1 F cap as example.
(500 mV)(1 F) / (35 mA) = 14.3 s
That's how long a 1 F cap charged to 5 V can run your device at the worst case current draw.