How to give a few seconds of juice to my IPOD?

[AlainB]

Hi,

I am feeding my IPOD from a switched wire that is on when the car key is on ACC or ON position. I made an adaptor using a 7805 chip.

The sequence of the key switch is OFF-ACC-ON-START.

When I start the car, the IPOD goes on automatically along with my Alpine amplifier. I can then choose the music I want to listen.

When I turn ignition off, the IPOD turn off.

When, for instance, I stop for refilling the gas tank, I stop the motor but I leave the key to the ACC position so the music continue to play.

Until there, everything is fine.

But for the one second or so it take to restart the engine after filling, the IPOD is not feed by the ACC wire so it "reset itself" so to speak loosing the song that was playing and the directory I was in.

Now, I need a way to keep the IPOD on ( 5 volts, 60mA ) for just the short delay that it take to start the car.

Any help is welcome.

Thanks!

Alain


**broken link removed**

 

[jimlovell777]

You could use a large cap or simply power the mp3 player through an always on connection that turns off after a few minutes when it detects the ACC line goes low.

 

[AlainB]

Yes, it is more like a MP3 player. I tried many capacitors before posting without luck. The biggest one was 8000 uF, with and without a resistor and it was not working. How huge would it need to be?

 

[jimlovell777]

How did you connect the capacitor? If you didn't add a diode the stored charge went to other systems, not just the mp3 player.

That being said my real suggestion was option two, it adds complexity but would be more reliable and useful in my opinion. If you really want quick and dirty use the cap but prevent it from back feeding other parts of the car.

 

[bychon]

It goes: switched power wire, diode (1n4003 or better), then a large cap (rated at least 25 volts), then to the mp3 fella. 100,000 uf might be enough.

 

[mneary]

If you're placing the cap before the 7805, it needs to be (seconds)*(current)/(max-min voltage).

Your max voltage in this case is the voltage after the diode, when the ACC position is on. I'll say 11V.
The min voltage is the lowest voltage you can give the 7805 and still work well. With a light load, a 7805 is good to a little less than 7V.
(max-min) is 4V
I'll calculate for 1.0 seconds.
The current is 0.06 A (60mA).
1.0*.06/4 = 0.015 farad, or 15,000 microfarads for each second you want to hold up the load.