What is the best way to power an Arduino with a 12v car battery?
Would this be a good solution? http://www.aaroncake.net/circuits/cdsupply.asp
The Arduino already has a regulator built-in so in theory you could just hook the car battery up to it directly.
Now if the car battery is actually in the car, I would worry about overvoltage transients and the like ... the car is a pretty hostile environment. Having a 12V-->9V regulator like the one you link to might be a nice insurance policy.
Would this be a good solution?
Absolutely not: that circuit is doomed. Sooner or later the car will generate a voltage spike that fries it.
But there's a simple protection circuit that will almost completely eliminate that risk.
Start with a diode (any old 1N4000-series will do) in serieds with the positive supply to protect against negative spikes. Follow that with a series resistor chosen to drop about 1-2V at the maximum expected current draw (i.e., if you're going to use about 200mA, use an 8-10 Ohm). Then add a Zener in the 20-30V range to ground. The resistor and Zener will absorb any big positive spikes.
If you replace the 7809 in your example circuit with a 7808, you'll have a nice clean 8V going into the Arduino while the car is stopped or the engine is running. However, while the engine is being cranked to start it, the car's voltage will sag quite a bit (8V is considered "acceptable" under those conditions), so the 7808 will drop out of regulation, and the Arduino will almost certainly reset itself.
If you're not hooking up much to the Arduino, and it's not using much power, you can eliminate the 7808. If you are, it's probably better to keep it, so you're dissipating more of the waste heat from linear regulation off the board.
Ran
Hi,
You can also use TVS diodes or Varistors.
http://www.maxim-ic.com/appnotes.cfm/an_pk/4240
Regards,
Igor R.
In this thread:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1236735887/15
there is a picture of a protection circuit for a car mounted project. You can try it.
Also Mike has some ideas in his pages:
http://www.thebox.myzen.co.uk/Tutorial/Protection.html
The Arduino already has a regulator built-in so in theory you could just hook the car battery up to it directly.
I've done this with a standard Duemillanove and it works well for moderate loads (200ma and even up to 500ma). Beyond that you may want to consider a switching regulator. My setup is a boat with an alternator pushing the voltage up to 14.4V when charging.
I believe some credit is deserved for the Arduino design as it includes reverse voltage protection, ripple suppression capacitors and the 7805 power regulator is in itself a very robust chip with several protection schemes included. Keep in mind also that a car battery acts as a gigantic capacitor with excellent noise/ripple suppression.
There are all sorts of things that can cause problems related to power supply (e.g. disconnecting a battery terminal with the alternator spinning) and accordingly there is hardly any limit to what you can add in terms of protection against potential threats. Unless the device you build is very expensive I would not worry too much until real issues surface.
What always makes sense however is to add an inline fuse between the Arduino and the wiring to your battery. This is not to protect your Arduino, but rather the "vehicle" (car, boat, RV, other) which house your device and possibly people as well. A car battery can easily supply several hundred Amps for many seconds and as such fried supply wiring and potential fire is a real threat.
I´ve tested in a car and bike without problems. I´ve only added a varistor between Vcc and Gnd.
How BenF said, the diode for reverse voltage protection and capacitor is already in the pcb.
Regards,
Igor R.
Absolutely not: that circuit is doomed. Sooner or later the car will generate a voltage spike that fries it.
Funny, I've got a GPS engine powered by the exact same power supply as that arduino (7805) that's been running fine for about 5 or 6 years.
If you've got a way to deal with the heat from the regulator, just plug it up to the arduino's DC jack and go.
-j
Igor,
What properties varistor did you use, i.e. what was its breakdown voltage. Would 12.7V be too low?
Thanks
Pete
It´s a 14 Vrms (S14K14)=> http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=204-1902&x=16&y=7
Regards,
Igor R.