# How do i monitor battery voltage and adjust engine idle with a servo?

This is a question about an onboard generator for a robot. Obviously id like to achieve homeostasis at around 12.5-13v. When my car battery reaches full capacity (13.8v) the servo releases the throttle. When it falls below 12v it increases idle to full. Im new to the game go easy on me im waiting on my pic programmer to get here let me know if theres an easy way to do it. -Brian

5 years ago
"When my car battery reaches full capacity (13.8v) the servo releases the throttle. When it falls below 12v it increases idle to full."

Is that what it does? Or is that what you want it to do?

If you want it to do that, you'd use a comparator with setpoint of 13.8V*. Add some hysteresis, so that it actuallly switches on at at 13.5V and switches off at 13.8V. Have your PIC turn change the idle, accordingly. You'll probably have to filter it so you don't get false alarms from noise. Or you could program the PIC to do some oversampling.

• you'd need a power supply of over higher than 13.8V in order to do this directly. The way to get around it is to run the comparator off of 10V with a linear regulator. Then divide the battery voltage in half with a voltage divider, using 2 equal high value resistors between positive and negative terminals. Then feed that to the comparator which will be set to around 6.9V.
Clear as mud?
impellbm (author)  klee27x5 years ago
yEA THATS WHAT I WANT TO DO WITH IT. but im new to this stuff so i have little clue what most of that means. Im using a lawnmower engine and a car alternator, to charge a battery for electric gear motors. But i dont want it to scream all of the time so i figured when the battery is full it should kill the idle. Get me? Do you have any websites that show me a schematic to use for this? Thanks a lot for the input. -Brian
bitshifter5 years ago