I am looking at a project where the arduino will be installed in a car. I am wondering what the best way would be to power the board. I am afraid of hooking the board directly off the power because of the power spike when the car is turned over.
For the power are you taking about directly from the battery
To be honest I am talking about what ever works. I was thinking of tapping into the battery and the ignition switch so I can know when the vehicle is off and I can safely shutdown.
I have mine running in a car, but have the power runnign through a 7812 voltage regulator first, and then to the arduino. no problems yet.
I run my decimila straight off a boat's marine system at ~12.5V. I run it for about 10 min at a time. Spec's 'recommend' <= 12v, but I haven't had any overheating problems at 12.5V. Someday I'll regulated it down probably.
This has been discussed before and from memory the conclusion was that you can power a decimila direct from a car's supply.
(Note, the car's supply is nominally 12V, but when running the voltage is elevated to 13.5 - 14V by the alternator).
My feeling on this is that I would be more comfortable with a regulator of some sort before the decimila. Orac's suggestion of a 7812 is probably the way I would go, but might consider regulating to a lower voltage so the onboard regulator has less to do.
I would probably also over-heatsink the regulator. Am I paranoid? lol
Mike
This topic probably needs some experimentation, and definitely needs a playground article. 
The Duemilanove and Diecimila use an MC33269 regulator that has a maximum input of 20V. The ARduino NG and other variants I am familiar with use a 7805, which typically has an even higher Vin.
The potential issue is heat; in a linear regulator excess power is dumped as heat, and in the Duemilanove/Diecimila/NG designs the PCB is the heat sink. This limits how much heat you can tolerate. How much is too much? I'm personally not sure, but I would guess a bit more than everyone else seems to think.
If you plan a high duty cycle (e.g. 24x7x365 operation), a high current load, or a poorly ventilated location, I'd use some external regulation. f you want to plug it in to the cig lighter and leave the bare board in the cupholder while you drive to work, go for it.
-j
PS - Here's an anecdote (since it's not an Arduino): I got an old GPS engine and powered it with a 7805 regulator directly off the vehicle battery. This thing is a power hog; it uses more power than an Arduino, therefore generates more waste heat at the regulator. It was powered on 24x7x365 (too slow to lock, so I left it on). I built it, stuck it in a plastic project box, and stuffed it in my truck.
The inside of a vehicle in the Alabama summertime gets pretty toasty - way over 100F easily. My GPS flaked out, due to the combined heat of the 7805 in the plastic enclosure plus the heat of the blast furnace vehicle it was in.
I took the circuit, pulled it out of the plastic box and mounted it into an aluminum one. The 7805 heat sink got removed and the 7805 was riveted directly to the Al enclosure. That particular configuration worked problem-free, heat-wise.
Hi
I would go with 78L05, provides you with 500mAh.
Your arduino should use somewhere about 100mAh at a maximum.
Use a diod 1N4001 to prevent paeks on Vbat and two capictors 0.1uF 20V on input and output of 78L05.
Or just buy a simple usb charger for the car and use tha hardware in it.
It will depend a lot on how careful you want to be. TERRIBLE THINGS happen on the automotive supply rails, and they can fry electonics pretty quickly. (see http://www.automotivedesignline.com/howto/205101011, for example.) There are special regulators designed to deal with this (the lm2931 is often mentioned), but the arduino doesn't have one.
I would feel pretty good if there were an additional regulator between the auto power and the arduino. Something designed to power a 9V electronic device, like this Ebay Offering (found via search; no experience with vendor or product.) These show up in thrift stores and as surplus frequently; a new one seems to be a substantial fraction of the cost of the whole arudino, and may not be worth the money.
Also anecdotal, but I've been running a Freeduino (Decimilla-style) in my car and it's been continuously on for the last three weeks. The Freeduino has a beefier 7805, but I haven't found it even hot to the touch. On the other hand, I'm tapping into the behind-the-dash supply for the radio, which is coming off the car's own voltage regulator. So I suspect it is already fairly well buffered.
On the gripping hand, when I re-design the circuit I'm thinking strongly of throwing in some 12v zeners to crowbar any transients that do come down the pipe. For what I'm doing with it, the possibility of a brown-out now and then doesn't worry me.
watch out HULK, theres a difference between milliamps and milliamp-hours. mA is a measure of current while milliamp hours (mAH) is a measure of current x time.
1 Like
weirdo,
Thanks for correcting me, it is typing error, i was thinking of mA but wrote mAH.