Short term battery backup circuit

[AnalogKid]

A lot became clear when I was drawing the circuit based one your first sketch, this really is the first time I'm working on something like this.

A common interaction with people who are new to this is to convince them that a schematic, no matter how bad it looks or how incomplete it is, is a critical part of just about every *question*, not just the solution. In fact, I have a packaged response for it.

Paraphrasing Rear Admiral Joshua Painter,

"Engineers don't take a dump, son, without a schematic."

ak

 

[Swinkels]

Here is #17 reworked for using the car battery as the holdup power source. I adjusted the values of some components, but without real information about the device being powered they all are guesswork.

Did you know back in post #1 that the car battery would be the backup energy source?

ak

View attachment 60904

A bit late; but thanks everybody who helped me here! I've ben using this setup for about half a year now and it works great. Only thing I changed is R2, I'mb using a 1K resistor as with 10K it stayed on for over 20 seconds. With 1K the timing is around 10 seconds

 

[Bluejets]

So I'm looking for a circuit that provides 12v backup power for something like 10 seconds, and after that turns off. How would I do that?

Take a look here.....simple as.....

https://www.rcgroups.com/forums/showthread.php?1854050-Simple-Bus-Tie-Circuit-using-Schottky-Diodes