Hey guys! I'm back.

I need this to be short so here we go:

My friend has set up a wind-turbine to power his house off-the-grid style, and he wants to set up an alarm to tell him when the voltage goes to 12.6/12.7 . He would like to to be variable (a simple potentiometer would suffice) and he does NOT have a large budget for this project. Thats why he asked me. I never buy anything new, what college student can? And have allways salvaged and built anything I need.

But this one has me stumped. I know they make them, but the ones I saw were 200 USD and that is insane.

So I ask you:

What simple electrical circuit can alert the household when the voltage from a 12V battery bank has dropped to 12.6?

Thanks guys! I know I can allways count on you to be polite, to the point, and kind even in the face of my obviously basic electronic "knowledge".

Google for an opamp comparator circuit. Would be your best bet. You can also get voltage alarms for cars and stuff, though I don't know if they are adjustable.

Will this work?

Low Battery Alarm Car 12VDC Project Kit DIY | eBay

Not directly, but you could probably modify it to work. I couldn't say how though, as I don't have one. I think I've seen over voltage alarms too.

Here's a little circuit to get you started...

Circuit

It is a basic Voltage comparator circuit...


Jerry

Op amps =/= comparator...

Comparators are useful for making noisy signals very square; or, quite simply, to compare two voltages.

It goes something like this;

There are 3 pins on a comparator; + , - , and out

When the voltage on the + pin is greater than the - pin, it will output a positive voltage.

If the voltage on the - pin is greater than the pin, it will output either a negative voltage, or nothing.

By using a voltage divider, a la potentiometer, you can simply take the output of the wind generator, hook it up to the comparator's + input, and the - input to the voltage divider...

For example, if the voltage divider puts out 12 volts to the - pin...
While the wind turbine is putting out 10. The comparator will NOT be outputting anything, and thus the alarm/light will be out.

If the wind turbine is putting out 13 volts, the comparator would output a positive voltage;

This can be used to turn a relay on or off too, actually, if you want it to automatically stop charging...