Hooking electronic device to car

[DragonMaster0121]

How hard would it be to connect an electronic device to the car's power, so that when the car turns on, the device turns on, and when the car turns off, the device turns off.

I don't know a lot about cars.

Thanks

 

[Nigel Goodwin]

How hard would it be to connect an electronic device to the car's power, so that when the car turns on, the device turns on, and when the car turns off, the device turns off.

I don't know a lot about cars.

Just connect it after the ignition switch, most cars have a suitable switched output called 'auxilary', used to feed the radio.

 

[evandude]

That is totally fine for small things, but the auxiliary line isn't intended for high current use, so if you are trying to power something that uses a lot of current then you should use the auxiliary line to switch a relay that will connect your circuit directly to the main unswitched 12v line from the battery.

that's why car audio amplifiers have a large wire that goes directly to the battery, and a tiny little wire that goes to the auxiliary line; it just uses it as an indicator, switching on and off the main power.

but you won't have to worry about it if you're only thinking of some small circuit, even something up to a couple amps might be okay depending on the car and how conservative they were with wiring and fuses. 8)

 

[DragonMaster0121]

thanks a lot!

 

[DigiTan]

Are there are any real good sites in general for explaining how to get to this wiring in general (tools to use, reattaching, etc). I'm afraid I wouldn't be able to put all of it back together.

 

[Russlk]

A repair manual for your car, from the local auto parts store will be a help. The store will also have splicing tools for making connection without breaking a wire.

 

[evandude]

you can buy crimp-on insulation-displacing connectors at auto parts stores so you don't have to cut any existing wires to tap in. the radio is usually the easiest place to find the aux line (unless your cigarette lighter is switched by the ignition as well, my car isn't but some cars are) but if you can get your radio out, you can just probe the wires with a multimeter and see which one switches on and off with the ignition, then just tap into it, simple as that. if you can get a wiring manual for your car, you should have no trouble finding a wire to tap into... surely you can find some in the fusebox, which may be even easier to access than the radio, depending on where it is in your car.

 

[instruite]

Just for your information
For a normal car, having a 12V battery the voltage is specified from 6V-16V in normal operation, 24V or 36V (depending on alternator) abnormal voltage (which can be due to alternator failure) and 100V/150V spikes (for timeduration of microseconds).
all the electronice units we design for car make sure that the unit power suplly work in above conditions. so you should check the volatge specification of the electronic device for the range of supply voltage and also protection from spikes

 

[stevez]

Make sure that anything you change results in all wiring being protected against overcurrent situations. While obvious to some it may not be to everyone.

Wires and other conductors that carry current have limits to their current carrying capacity. As the current thru a wire increases the wire (or PCB trace) gets warmer - if taken to the extreme it simply melts. Fuses, circuit breakers and other devices are made to interrupt the flow of current at select amounts- usually long before the wire can get hot enough to cause a fire.

An example of a dangerous situation - connecting a 24 ga wire to a circuit that is protected by a 15 amp fuse. In a fault situation (one you might not ever predict) the wire could get hot enough to cause a fire.

Other cautions - watch out for the SRS (airbag) circuits. Fire one of those and you could get killed - or at the very least it's an expensive repair. Use caution around any circuits that can affect the operation of the engine - engine failure while cruising on a highway can result in some terrifying and dangerous moments.