So I am building a NFC unlock for my car using an arduino and an NFC reader. So this means the arduino should be on all the time, unless you can think of a better idea. Right now I plan on having a 6v 1W solar panel charging two 120F 2.7V super capacitors in parallel while the car is off. Then once the car comes the capacitors will be charged by the 12V car battery. So I need to figure out a way to switch between the two power supplies.
I need some recommendations on how I should go about wiring this circuit. Should I use a LiPo instead of super capacitors? How can I keep this arduino running all the time without sucking the power source dry. Any suggestions are much appreciated. See the image below for a rough schematic of what I'm doing.
I wonder whether it's necessary to go to all this trouble.
What current does your Arduino with NFC reader take?
I suggest you simply power directly from your car battery via a switching regulator. The regulator will roughly halve the current required. You can work out how many days it will take to discharge your car battery by say one-tenth of its ampere-hour capacity.
Beware of big transient spikes on your car battery!
Wouldn't it be much simpler to power the Arduino from the car battery?
If necessary, arrange for the solar panel to top-up the car battery?
Alternatively (if you are concerned about discharging the car battery so the car won't start) have a second 12v battery separated from the car battery by a diode so that, even if the second battery is flattened, the starter battery will be OK.
...R
arduino not recommended.
you can use a chip, run it in sleep mode and cut the power way down.
the arduino boards use too much power
there are lots of examples on this list
search for sleep
I don't think the sleep mode option will work being I always want the NFC reader to be active. I am going to do a test to see the current draw of the reader.