[quote name="ducatiboy"]You are right, normally a car battery will get rid of all but a fraction of voltage spikes, but it only takes 1 to blow out a circuit.
You might want to make the zener a little higher. It's not uncommon for some alternators and regulators to run close to that normally.
Something else I learned, that some portable battery jump start packs run at 24V's. So just incase anyone will ever use one of those, you will want to make sure this circuit can run off 24V just incase. That was a surprise to me.
There are all sorts of voltage spikes.... from the fan motor
