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Discussion Starter · #1 ·
Hi, I'm new here... I'm also relatively new to car audio electronics, but not so new to electronics (have designed some custom circuits, made PCBs, etc).

At the moment I'm building a simple RC delay circuit (basically putting a capacitor inline with my deck's ignition wire, with a diode to keep the cap from backfeeding into everything else on the ignition wire). The idea is to keep my deck from immediately powering down if I'm trying to switch from ON to ACC (which is on the other side of OFF & LOCK in my truck). If it makes a difference, the truck is a 2007 Ford Ranger.

I know car electrical systems can be terribly noisy places... I have a cap rated at 50V and the diode is rated at 1000V/10A (yes, one thousand). Should these be able to survive any incoming transients from the alternator/etc, or would it behoove me to put, say, a 20V reverse-biased zener across the cap to make sure that any particularly huge spikes don't pop it?

Space isn't a big issue, as I have one of the newer discless "media players" that's only about half the depth of a standard CD player deck (and my truck was designed for a double DIN unit so I have spare room to play with vertically as well)... so if the zener will help maximize the longevity of this circuit, I'm all for it.
 

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post schematic
 

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I think OP is just talking about this circuit with a Zener in parallel with the cap:


Need to know what component values OP is considering using.
I think OP is being paranoid about voltage spikes - no need for the Zener IMO.
 

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What voltage spikes? 10 to 15V? it`s nothing to be concerned.
 

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Discussion Starter · #5 ·
From what I've read, transients can far exceed 30V; the SAE documented that inductive load switching transients can approach 80V, and a load dump transient (ideally wouldn't happen, but the real world isn't ideal!) can approach 125V.

Cost isn't an issue as I have many parts laying around, and those I don't have can be obtained cheaply.

I'm just trying to figure out whether the zener (or a TVS?) would be a good "extra line of defense", or if it would just be superfluous.
 

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It's time to go from theory to practice,do it,share results.
I think it's unneeded but I've been wrong before

Sent from my SAMSUNG-SM-G925A using Tapatalk
 

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If you are trying to protect against a true alternator load-dump scenario, then I'm afraid the Zener diode may become a sacrificial component without any current limiting during the clamping cycle.

Here is an *excellent* article on automotive power conditions and protection treatments:

LINK -> http://www.industrologic.com/autotransients.pdf
 

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