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You could go directly from the battery.
But it is a much better practice to use a inline fuse or tap the power from the fuse box on the Accessory line.
use a regulator if you want <12V or if you want clean power, as I imagine 12V maybe somewhat noisy. I have used 12V directly without problems before... and use your own fuse rated at what your circuit is drawing.
the voltage at a car battery can reach 18 volts (maybe higher) while charging and there is a lot of inductive stuff (starter solenoid, airconditioner clutch) hanging off of it even under the best of circumstances. So it depends on what you are powering.
For sensitive electronic device, you had better put some protection device and voltage regulator.
But, most car accessories/equipment (e.g. car CD/DVD player is usually manufactured with all constraints in mind .... they have already incorporate voltage regulation, current/voltage protection, mechanical vibration protection, etc). Problem will arise when you try to connect home AV devices to car electrical system. They have different mechanical and electrical environment criteria.
And for Cherrytart, I think the appearance of 18 volt in a 12 volt environment means problem in car battery charging system. The voltage regulator should regulate the voltage to a maximum of 14.5 volt. I experienced this incident, my VR got broken and the voltage reach 18 volt in high engine RPM.
I am pretty sure, you know Murphy's laws.. ("If anything can go wrong, it will")
So, before something wrong happens to you, build yourself a black box with a low-droput regulator(s) such as: **broken link removed** or similar, and you be always fine ..
There is a very bad danger of fire if you tap directly from the car battery as it can supply huge current. it is better to use a protection fuse and a diode (in your ckt) and there is a possibility of getting voltage more than 12 v due ti charging ckt with some noises from the source so it is good practice to use a zener protection diode at the input with a series low resistance.
There is a very bad danger of fire if you tap directly from the car battery as it can supply huge current. it is better to use a protection fuse and a diode (in your ckt) and there is a possibility of getting voltage more than 12 v due ti charging ckt with some noises from the source so it is good practice to use a zener protection diode at the input with a series low resistance.
shmoib, you didn't mention the kind of cct you are going to use and its voltage rating.
Assuming a car amplifier with an IC designed for car use, then you dont need a lot of thinks.
In general, a series fuse would be enough. To eliminate noise from the ignition and charging system, use a series inductor and some large electrolitics for good filtering.
In the case your cct needs only 12V or less, then use a stabilised supply as suggested by other people above.
You can use all suggestions given, in your cct in order to increase protection.
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