capacitor

I installed a kenwood head unit in a 95 Buick Park Avenue. When the vehicle key is turned to the Off position, the deck should stay on until the drivers door is opened. What happened, is that the head unit would go Off, and then immediately start back up. Since it has a 20 second start up, it was very annoying. So I installed a 4700 capacitor on the red line, along with a diode to prevent the store current back feeding the whole circuit. Now the radio continues to operate just fine when the key is turned to the "Off" position. The capacitor is larger than necessary, because now the radio stays on for approximately 5 seconds after the door is opened. This works well for me.

My question comes in that if I am listening to the stero in the "Accsy" position, and then turn the key to the "Start" position, the radio will go off immediately, and then after releasing the key to the "run" position, it will go through the 20 second start up procedure. I am kind of surprised, because when power is interupted by opening the door, the capacitor has enough power to operate the battery for 5 seconds. Why wont the capacitor operate the radio while the key is in the Start position for only 2 seconds?

Because your main power is switches via the ACC circuit which cuts off during cranking.

Your cap may not be holding up the "power" to your Kenwood, but merely the voltage on a sense input.
Else it may be just a short dip in the power circuit - enough to reset the Kenwood - that the cap is able to ride through.

Parallel another cap across the one you have.  Your radio may stay on for 10 seconds after the key is turned off, but it may keep it on through startup.

Does your head unit turn of when starting? I know alot of vehicles cut off non-essentials (ie. radio) when turning over to use full power to the starter.

It does, but my question is how do they accomplish this? The yellow memory wire is constant 12v. So I would expect the capacitor to keep it running during the few seconds that the engine is cranking in the start position.

Did you try adding a second capacitor? When switching from on back to acc does not have the voltage drop associated with starting the car. I really think a second cap will work. The only trade off will be that the deck will stay on for 10 seconds instead of the current 5 seconds.

i am an idiot wrote:

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Did you try adding a second capacitor? When switching from on back to acc does not have the voltage drop associated with starting the car. I really think a second cap will work. The only trade off will be that the deck will stay on for 10 seconds instead of the current 5 seconds.

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Thanks, I plan on trying that but haven't had a chance yet. My post was actually to the previous reply. It staying on for 10 or 15 seconds, even one full minute will be fine if I dont have to deal with the reboot.