What is typical car battery current?

**powerslide** · 09-21-2004, 11:06 PM

I am wondering which capacitors etc to get for my circuit.
I have no idea where to start.
I have a 1992 BMW 318 with 2 batteries and a brand new alternator putting out about 14.2V when the car is running.
Basically I want to know which capacitors I should use if I want to hold the power line for 15-30 minutes, and which size relays i'll need for my circuit.
Any help is appreciated, Im sort of in the dark here.
If someone could explain I'd be greatfull, perhaps I need to use a tool to measure my 12v line's output?

**vcbb5** · 09-21-2004, 11:12 PM

What kind of power system are you trying to use (OPUS, Inverter, other), and are you making a shutdown/startup controller?

**powerslide** · 09-21-2004, 11:32 PM

Sorry should have been more clear.

I am running power straight from my battery to the inverter, and the inverter to the computer.
I have created a circuit (using a shutdown controller on this board through the serial port) with a series of relays that will control the start up and shut down of the carputer not on the ignition line, but on the stereo deck 12v input line, which is similar to the ignition line in functionality.

I hope to have a capacitor at the start of this circuit that will hold the charge for about 15 minutes, so that I can go away from the car for short breaks and the computer will still be running when I get back in the car and the stereo comes on. This will re-fill the cap.
However when the 15 minutes is up, the current will drop from that part of the circuit, closing relays and setting the computer to hibernate. The current flows to another cap, which will hold the charge for a much shorter time so that the computer can safely hibernate, then that will run out and the inverter will have power cut.
phew hope that makes my intentions more clear

**powerslide** · 09-21-2004, 11:34 PM

also, when the line is dead and I turn the car on, the current flows through the set up and my one shot circuit will fire and bring the comp back from hibernate.

**vcbb5** · 09-21-2004, 11:38 PM

I've soldered in my relay 4 different ways and it still won't work. Help please.

here is my post doing about what you want to (but without time delay shutdown). I looked into the time delay, and it just wasn't easy and was beyond me. The way i did it, the inverter shut down after a soft shutdown of the computer, but if the comp hangs, your inverter stays on.

**powerslide** · 09-22-2004, 12:07 AM

thanks vcbb5, that is very similar to what I was thinking.

Should I use the same value caps etc as you?

Also, I really need to have the time delay. Hopefully I can work it out.