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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

klee27x5 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
marksrone5 years ago
bitshifter5 years ago
you should also be aware that when you put a large load on a motor powered by a battery, the voltage can and will sag. A car battery under load from the starter motor sags from about 13-14 volts to about 10v, this is normal and does not mean that the battery needs to be charged. It's more work, but adding a current sense resistor and calculating how much energy has been expended from the battery and charging after you have taken out, say 10-20 amp-hours would probably be a better route so you aren't constantly throttling up the engine whenever one of your electric motors gets loaded down. The other thing to consider would be how much energy you can extract from the gas engine at idle compared to your average energy budget. You may be able to get away with just gearing (changing pulley sizes) so that your alternator produces enough juice to trickle charge your battery while your robot is running, then you won't need to muck about with throttling it up and down all the time.
Abhishek.D5 years ago
I cant tell u adjust engine idle but i can tell u the other. take a compass.put it on a piece of woob i mean wood. now wrap 150 turns of insulated coil around the wood. ... ... ... ZZZzzzzzz zzzZZZzzz ZZZzzzZZZ huh oh!!! slide the coil of the wood carefully and you will gaet a square of coil. put it on the wood vertically. take the ends and connect the left piece(negetive),right piece(positive) to cheak voltage.
impellbm (author)  Abhishek.D5 years ago
Im really lost on the purpose of this answer...
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