I'm confused.
Is the LM317 configured to deliver a constant voltage or a constant current?
It can be configured either way.[/QUOTI
I think constant voltage. That's what i set the potentiometer for - a specific voltage

 

To clarify, the circuits work as they are supposed to. I have hooked up each one to a plug-in 12V, 3A DC battery charger and set the potentiometer so that the sensor is getting the right voltage. However, now I need to hook them up in parallel to a 12V, 800A deep cycle marine battery to deploy in field. Now that I understand what that looks like and how to hook together, I am trying to determine how many sensors I can connect to one battery and if 18 AWG wire is adequate to hook to an 800A battery. Specifically, does the ampage of the battery (source) matter for the wire gauge or is it the ampage of the sensors (load) that is important?

 

Specifically, does the ampage of the battery (source) matter for the wire gauge or is it the ampage of the sensors (load) that is important?

The battery amperage rating is not important as long as it can deliver the load current.
The load only takes the current it requires, so that's you only concern for the required wire size.

But you should put a fuse or circuit breaker in series with the battery, to protect in case of an accidental short, so it doesn't fry your wires or start a fire. Otherwise such a battery can deliver several hundred amps to a short.
The fuse/breaker rating should be about 50-100% higher than the maximum total current you will draw from the battery.

 

The battery amperage rating is not important as long as it can deliver the load current.
The load only takes the current it requires, so that's you only concern for the required wire size.

But you should put a fuse or circuit breaker in series with the battery, to protect in case of an accidental short, so it doesn't fry your wires or start a fire. Otherwise such a battery can deliver several hundred amps to a short.
The fuse/breaker rating should be about 50-100% higher than the maximum total current you will draw from the battery.

I have some 250V, 1A fuses - so would I put that between the battery and the first circuit?

 

I have some 250V, 1A fuses - so would I put that between the battery and the first circuit?

That'll do, but a self resetting PTC fuse might be more convenient.

 

I have some 250V, 1A fuses - so would I put that between the battery and the first circuit?

Yes, and as close to the battery as feasible.

 

I'd like to go back to the basics on this!

Consider the sensors. You talk about them having a 'different resistance', but from your description of what you are doing, it seems the 'sensors' are actually quite sophisticated, delivering a fixed current to some form of heating element on one of your probes, then being able to measure the temperature at both of the probes and store this information somewhere. Or have I misunderstood your explanation?

If this is correct, then I would surmise that the only requirement is to provide adequate stable power to the 'sensors'. I put that in quotes because these would seem to be a lot more than just sensors, as indicated above. If this second surmise is correct, then the problem is essentially simple to solve.

If your multiple sensors are in different trees some distance apart, then you may need one of your regulator boards at each tree, to ensure a stable supply. In this case, you just bring all the battery connections back to a single point and connect them (through a fuse, as Crutschow suggests!) to your big battery (first picture).

If your sensors are all within a couple of feet of each other, then you could simply use a single regulator board (or dual board, if that's the way you are making them) and connect the sensor power lines to the output(s) of the regulator (second picture). If you are using, say, 12 sensors, each requiring around 110mA then the single regulator should be quite capable of powering them, though a bigger heatsink would be sensible.