Low current battery protection / switch off

[Bk1]

My idea is the following ;
The car does not have a warning signal to tell me I have left on the lights when I turn off the ignition. In multiple occasions I have returned to a car with a dead battery.

Annoying as this problem is I want to build a circuit which will detect the current on my battery and kill the power to all "current-using" components. I would like the switch off the power when my battery goes below 12volts. In order to prevent the circuit from swichting on and off at the 12V border I would like to use a regulator for the current ( for example : L78L061Z ) so I can run everything on 6volt ( hysteresis window ).

I have a very limited knowledge of electronics and I was wondering if someone here could give me some tips or a drawing of a circuitboard ( maybe in microcap, etc.. )
Please excuse me for the mistakes in this post since I do not master the English language completely )

Kind regards
Tim

 

[MrAl]

Hi Tim,

Monitoring the car battery current is a little harder than most measurements because the dynamics in the current levels changes wildly over various operations in the car. Still, they do make meters you can buy and install that will tell you the current level. An auto parts store might help here.
To get good monitoring of the low level currents that run things like small lights in the car, you could try sensing current yourself with some kind of current monitor chip. You'd want to monitor only the current to the accessories though, not the starting current. One glance at the readout would tell you if the current is still there or not, and remind you to shut off the lights.
Did you ever build an electronics kit and solder components?

 

[Bk1]

Thank you for your reply MrAl

Thing is that this is actually a little project I'm going to make in class together with 2 friends. We are not actually building this in to a car and because of that it would suffice if our circuit would work with a battery which we can lower in current by hand.

The circuit should simply compare the current from the Battery with a reference current ( I don't know the correct terminology in English sorry ) and if it would spot the battery dropping below 12, it should switch off a light ( simple 12v bulb )

thanx again for the input!

 

[MikeMl]

Mr BK,

you seem to be confused about Current vs Voltage. I think you are trying to disconnect the loads (lamp) as the battery Voltage decreases as the battery discharges due to the Current being drawn from it.

I have posted a circuit which will work for this application in these forums. However, before I give it to you, I would like you to answer some questions:

If you are going to put such a circuit in a car, where in the car's wiring would you put it?
Would you break the circuit to the starter motor, for example?
Would you break the circuit to the electronic engine control unit?
Would you break the circuit to the ignition key switch?
Would you break the circuit to the in-dash radio?
Etc?

 

[Bk1]

I may have mistaken them both indeed. Thank you kindly for your answer.
My appologies that I was not able to reply to you a little bit sooner but it was not possible.

The circuit should stand loose from a car and work on a 12V battery which we can lower in voltage.
I would not break the circuit to the starter motor of elektronic engine control unit.
The circuit should just be able to cut the power to the lights when the battery voltage is to low.

I would help me a lot if you would be willing to post the circuit.
Thanks again for your help.

Kind regards