Further to my two, other questions about Zener diodes to detect when an automotive battery is being charged by the alternator, I've developed the following:
Note: The Fritzing tool I used doesn't have a breadboard symbol for a 10-14v supply, so I've used a battery symbol to make clear which my positive and ground rails are.
The schematic looks like this:
My main question is, is this circuit correct?
If I understand things correctly, (unfortunately not the results I am seeing in the real world):
- The Zener diode should break down at 12v, it doesn't - it's always letting through < 0.1v regardless of the input voltage in the range of 1-12v. Past 12v there's a marked increase in the throughput of the zener diode, consistent with what one would expect.
- It's not immediately obvious from the data sheet whether I should wire my reference, or the variable source to the
+of the LM311. I've done it the way below.
- I'm told, as this is an open collector IC, I need a pull-up resistor to
I also have some questions:
- How can I calculate how much power this circuit will use "at rest", i.e in order to do almost nothing until the alternator is running, without placing a demand on the battery?
- Is this the only/best way to detect a running alternator?
- Given that my reference is 1.26v from the rechargeable button cell, I will eventually need to connect something to recharge that when the system is running.
Where does one find a freelance electrical engineer who could design such a circuit to a list of constraints and produce a simple schematic/PDB that meet the requirements?