Help with voltage monitor alarm please.

[Lascannon]

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".

 

[Things]

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.

 

[Lascannon]

Will this work?

Low Battery Alarm Car 12VDC Project Kit DIY | eBay

 

[Things]

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.

 

[lasersbee]

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

Circuit

It is a basic Voltage comparator circuit...


Jerry

 

[Hiemal]

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...