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Old 06-06-2013, 03:09 PM   #11 (permalink)
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I'm sure in my younger days I hooked up a radio by running a wire straight to the battery.


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Old 06-11-2013, 01:43 AM   #12 (permalink)
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Originally Posted by Diesel_Dave View Post
I always figured it was just because "non-critical" electrical draws are shut off during cranking to ensure the maximum allowable energy is left available to get the engine started. If you can't get the engine started, the radio doesn't matter.
My Subaru does this (radio shutoff when cranking the engine) and I always figured it was for the reason Diesel_Dave posted above. Interesting that your circuit worked. I'm annoyed by the 3-5 seconds it takes for my Subaru (Clarion) radio to re-boot after an engine re-start but not annoyed enough, yet, to try a fix. Maybe later. Good work.

Oh, meant to mention that maybe you'd want a current limiting resistor between D2 and C1 to limit in-rush current when you first charge C1 but, heck, if it works and doesn't blow Fuse F1 then ... far out!
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Old 06-11-2013, 03:23 AM   #13 (permalink)
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I just have a tape deck in my Forester.

I wonder if I actually own any tapes...

I did not have a car when I lived in Germany, I just listened to Internet radio, just like I am doing right now, but it always seemed like the German stations played American music with German commercials.

I always found it to be amusing. People always change channels for commercials, but I never had any idea what they were selling!
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Old 06-11-2013, 10:29 AM   #14 (permalink)
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First off, yes, it was a problem on my '97 Civic. Restarting the engine caused the radio to shut down and reboot. The problem was worse when listening to CDs or when listening to any spoken material - if you miss a couple words you can lose the whole thought.

Another project provided insight into what was happening. I installed TWO deep cycle batteries in the trunk and deleted the underhood battery. I installed a new stereo and had the option of powering it from whichever battery I chose.

One battery powers the starter motor and headlights. The other powers everything else, including (currently) the STEREO. This works well. Key-starting the engine does NOT reboot the stereo. However when I wired the stereo to run off the battery that powers the starter, key-starting the engine DID cause the stereo to reboot.

So I deduced -
Nothing in the car's logic circuitry cuts power to the stereo when keying the engine. However, the voltage drop of starting the engine does cause the stereo to cut out and reboot.

Note - this installation has both positive wires for the stereo powered by the same battery. There is some possibility that by running these two leads off different batteries one could also avoid engine-start stereo shutoff, but I didn't take the time to test the various possible combinations.

Modern car stereos have one positive "constant power" lead which keeps the clock and memory going, and also provides the necessary current for its other electronics. The other positive lead could be called an "enabler". It is switched on/off by the ignition switch. The stereo will run or can be turned on only if that lead has power, but it really only permits the stereo to run, doesn't provide a significant amount of power. I didn't take the time to wire the two leads to separate batteries to see what would happen.
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Old 09-29-2013, 04:26 AM   #15 (permalink)
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list parts?

@arekkocowicz: I have the exact same problem with my Mini cooper and a new head unit (Kenwood). I don't have a good oscilloscope to check the voltage drop from my battery, so just for testing purpose I connected the yellow +12v constant cable from my radio to a stabilized power supply, with the ground attached to the chassis of the car. and as you guessed when I start the engine the radio didn't turn off anymore.
so I need to create the same circuit as you did.

Did you made improvement to your circuit?

could you provide a list of the parts you used with their respective values?
I know you used Su'scon 5.5F 2.5V x6 for the capacitors, but what about the diodes and fuse?

and where did you bye the Su'scon capacitor?

thanks for your help!

Last edited by lmn; 09-29-2013 at 04:33 AM..
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Old 10-01-2013, 12:29 AM   #16 (permalink)
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The start position of every car I've seen, cuts power to accessories. Even if you disconnect the starter, and there is no power draw, the start ignition position will kill accessories. If it was really a current draw issue, then the headlights would shut off long before a stereo that draws only a few amps. And my headlights certainly don't shut off when I'm cranking the engine(I bet yours don't either).

The solution is to reroute the ACC feed to the stereo, so that it isn't going through the start position.
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Old 10-01-2013, 12:39 AM   #17 (permalink)
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headlamps are connected to a constant +12V in every application i've ever seen. this is why you can accidentically leave them on with the ignition off and kill a battery.

i'm sure there are exceptions to this now though.
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Old 10-01-2013, 12:41 AM   #18 (permalink)
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Originally Posted by RobertISaar View Post
headlamps are connected to a constant +12V in every application i've ever seen. this is why you can accidentically leave them on with the ignition off and kill a battery.

i'm sure there are exceptions to this now though.
Yes, and no. Subarus all have them wired through the ignition switch, ON position. VWs have the parking lights wired straight, but headlights wired through the ON position. A few other cars have similar things.
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Old 10-01-2013, 02:35 AM   #19 (permalink)
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When I have bothered to put a stereo in a car, I always got the 12v power from the reverse light circuit. That way you don't have to run a wire to the battery, just to the fuse block, it's protected by a fuse, there is rarely any other draw on the circuit, and whenever I have done it the reverse lights were one of the constant power circuits (as in they stay on when you start the car), but the circuit will shut down when you turn off the key so you don't have to worry about leaving the stereo on and killing the battery.
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Old 10-01-2013, 02:02 PM   #20 (permalink)
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The radio shutting off when cranking is not a problem.
The radio is supposed to shut off when cranking. It is switched to do so.

This is because the inductive current draw from the starter can put a massive voltage spike into the electrical system when cranking stops. By shutting off electrical accessories that are sensitive to power spikes, the manufacturer avoids the chance of damaging them.

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