how could i wire up a circuit to click a relay when a certain voltage is detected? ~8 volts for example. it wont click if its above 10 volts or below 6.
That would be a fairly complex circuit.
The first thing you would have to do is create a stable voltage reference, which can be done with a 7805 voltage regulator.
You would then have to scale the voltage you are trying to monitor - typically cutting it by 66% works well with a 5vdc reference. This can easily be done with a voltage divider circuit.
For the limits you could use an op amp for each limit. You would put your scaled voltage on one input, and the wiper of a pot on the other input. The pot will be set to the limit. For the upper limit you'll need to put the pot to the (+) input of the op amp and your scaled voltage ot the (-), for the lower limit you'll reverse it, put the wiper on the (-) and the scaled voltage on the (+).
You would then need to take the output of each op amp and run it to a 2 input AND logic gate. The output of the logic gate would need to go through a transistorized drive circuit and then can be connected to a relay.
A simpler approach would be to utilize a microcontroller. You'll still need the voltage divider to scale the input voltage but all the limits can be handled in the software. You would also still need the transistorized relay drive output.
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Kevin Pierson