Modding temps sensors to get delta?

[Alexandr0s]

Okay, to give everyone a short explanation: I recently got a T-Balancer BigNG, because I wanted a new fancontroller. I was hoping it could work with delta T, but after searching their forum for a couple of minutes, I discovered that they haven't implemented it into their software. So I was wondering, is it possible to do by modding 2 analogue sensors?

The reason I started wondering is because of the way fans use the molex 4-pin power. Those 4-pins have a +5V, a +12V, and 2 GND. If you connect the +5 and the +12 to the fan, you get the difference in voltage, namely +7V. I know those sensors work completely different, but it got me wondering anyway, is it possible to rewire 2 sensors to show the difference, instead of both outputs?

The BigNG uses standard analogue sensors, with a 2-pins header. I assume the sensors are some kind of thermistor, a resistor which resistance varies depending on the temperature.

I hope someone is able to help me out, thanks in advance :).

[Alexandr0s]

I'll bump this hoping that anyone can help me :rolleyes:...

[Akula]

I think it is possible to do this, but it would require finding just the right two thermistors so that their summed value gave you a value that corresponded to a scale that the hardware could accurately use. Here is an example with totally made-up numbers.

Lets say that the delta T you are looking for is 20 degrees Celsius with 50 degrees Celsius at point A and 30 degrees Celsius at point B, temperature A minus temperature B give you the 20 degrees delta T. Your current single temperature sensor gives a value of 1000 ohms at 20 degrees Celsius. You would need to find a thermistor for point A gives a value of 750 ohms for 50 degrees Celsius and 250 ohms for 30 degrees Celsius. Wiring these is series would give the hardware the impression that the value was 20 degrees Celsius.

Now, unless these thermistors were perfectly chosen they might only be accurate at that one value, five degrees either way could be way out of the ballpark.

If you are interested, I have a simple circuit design that I can share for making a delta T, PWM controller that is pretty cheap to build so long as you don’t mind a little soldering.