Need to sense when 12V accessories are switched on for a motorcycle related project. Testing a voltage divider which seems to be perfect. R1 = 10k ohms, R2 = 4.7k ohms.
The problem is when I add a 5.1 Zener diode. Testing at 18v, the divider outputs 5.7v. When I plug in the Zener, it drops the output voltage to 3.6v. I tested the Zener (7v, 10mA output from my power supply) and it dropped the voltage down to 5.1, so I know it isn't the problem. What am I doing wrong?
Diode is: Vishay BZX85C5V1-TR