Voltage monitor for car battery

[b1arrk5]

I did not know that about zeners. I like many others have been taught that a zener doesn't conduct until you reach or exceed the avalance voltage. After reading your post I pulled out one of my textbooks, which states that this is the case. I then put together a little test circuit, and just as you predicted, my 5.6 volt zener diode was conducting at right around three volts! I had always assumed they would be within twenty percent or so.

Thanks again for sharing your hard won knowledge and experience.

Jerry.