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$25 Temperature Controller and Display!

A brilliant new temperature controller that's so cheap it's unbelievable.

By Julian Edgar

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You want to control an intercooler fan or water spray, display coolant temp and also control radiator fans, or operate a cooling fan on a car sound amp? Well, we’ve got the device for you!

And unbelievably, the module will cost you only AUD$25 delivered to your letterbox!

So how good is this? A digital temperature display that works straight off 12V and shows temps from minus 50 degrees to plus 110 degrees Celsius. It even comes with its own remote-mount temp sensor.

But that’s not all.

The display also has a relay output enabling you to switch on fans, pumps, warning lights or buzzers.

But it gets even better.

You can configure the system to switch the relay when the temp exceeds the set-point – or alternatively, when it drops below the set-point. And you can also configure a delay period so that the relay doesn’t keep tripping with short-term temp spikes.

Finally, for great accuracy, you can also calibrate the reading.

This is a great piece of gear which only a few years ago would have cost many hundreds of dollars.

So that’s the good news. And what’s the bad? Well the provided instructions are pretty crap – but that’s OK, in this article we’ll show you exactly how to operate the module.  

Where to get it

The module is available on eBay for AUD$24.99, including postage to Australia.

The seller is Super Electronics Parts and the device is listed as “DC 12V Digital Temperature Controller Thermostat C”.

Other versions are available that use mains power and/or display the temp in degrees F.

Description

The module is 78 x 71 x 29 mm (L x W x H) and uses a display window that requires a cut-out 70 x 28mm. It has a mass of 110 grams. 

It uses a LED display that shows temps up to 100 degrees C to one decimal place (eg 35.6), and above 100 degrees C in single units (eg 105). The update rate is fast (about 3 times a second) and the sensor is very responsive to changes in temperature.

In addition to the numerical display, there are two LEDs.

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One shows when the set-point has been exceeded. (The set-point is the temp at which you’ve set the device to activate its output.)  This LED has two modes – steadily on when the relay is activated, and flashing when the set-point has been passed but the module is running an inbuilt delay before turning on the output. (You can vary this delay time – more on this in a moment.)

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The other LED shows that the display is indicating the set-point temperature.

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On the face of the instrument are four push buttons – up/down arrows, Set and Reset.

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Wiring connections are by means of screw terminals on the rear of the module.

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The module doesn’t look at all cheap and nasty – in appearance it could easily be a AUD$150 instrument…. and that sentiment also applies to the internal build quality.

Making Connections

Displaying Temperature

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The simplest use of the instrument is to display just temperature. This requires only four wiring connections and no menu configuration.

Power (12V nominal) connects to Pins 3 and 4 – ground to pin 3 and positive to pin 4.

The NTC (Negative Temperature Coefficient) sensor that is provided connects to pins 7 and 8 – it doesn’t matter which wire goes to which terminal. With these connections made, the display should come alive and show the temperature at the sensor.

(Note: the thermistor wiring can be extended as required.)

The default values programmed into the instrument mean that straight out of the box, it will work fine as a digital thermometer.

Controlling an output

The module is fitted with a 5 amp relay. This means it can be connected directly to buzzers and warning lights. Through an additional heavy duty automotive relay, it can also control pumps or fans. (We’ll cover this application in a moment.)

To get a feel for how the control system works, it’s a good idea to play with it before installation. Let’s take a look at how it can be set up.

Pressing the Set button briefly changes the display to show the set-point temperature. This setting can be altered by pressing the up and down keys. When done, press the Set key again or simply wait a few seconds and the display reverts to the current temperature.

Pressing the Set button for 3 seconds brings up a second menu. Different parameters can be selected by pressing the up/down keys. To change the selected parameter, press the Set key a second time, then make the adjustments with the up/down keys. Whatever setting is selected is retained in memory, even if power is lost.

The available parameters are:

HC – this menu configures the module to either turn on its relay when the temperature exceeds the set-point (‘C’ mode), or turns on the relay when the temp falls below the set-point (‘H’) mode.

d – this sets the difference in temp between switch-on and switch off. (This is sometimes called the hysteresis.) By using the up/down keys, you can set this anywhere from 1 degree C to 15 degrees C. This is a very powerful control that can make a huge difference to how the system functions.

L5 – this is the minimum temperature the set-point can be configured. Normally, this would not need to be altered from its minus 50 degrees default.

H5 – this is the maximum temperature the set-point can be configured. Normally, this would not need to be altered from its 110 degrees default.

CA – this function allows you to correct the temperature display by adding or subtracting 1 degree units from the displayed reading.

P7 – this function is used when in C mode you don’t want the output cycling on and off at short intervals. The setting can be anything from 0 – 10 minutes. It example, if it is set to 1 minute, after the relay has activated once, it will not activate again until a minute has passed – even if the temp set-point has been tripped. In most uses you would set this to zero.

Over Temp Alarm

So let’s take a look at how you’d set the module up to turn on a warning buzzer if your turbo’d intake air temp exceeds 60 degrees C.

Press Set for 3 seconds then select the following:

HC – set to C

d – set to a small value like 2 degrees

L5, H5 and CA left at factory defaults

P7 set to zero

Press Set briefly then use the up/down keys to select 58 degrees as the set-point.

Huh? 58 degrees? We want the alarm to trip at 60 degrees, don’t we? This is the only trick in setting up the unit. In ‘C’ mode the relay will trip when the temp actually reaches the set-point plus the hysteresis – ie 58 degrees plus the 2 degrees we set in ‘d’ mode.

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Here is the wiring for the over-temp alarm buzzer.

Turning on Fans or Pumps

To operate radiator fans or a water/intercooler pump (or intercooler water spray), the menu set-up is the same as described above.

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This diagram shows you how to activate a heavy duty automotive relay than can control a fan or a pump.

Conclusion

For the money, this is just a phenomenal instrument. Having an accurate and fast-response digital thermometer is just great – but being able to smartly control a relay output is just amazing. The icing on the cake is the adjustable hysteresis and delay to prevent cycling. Oh yes, and the fact you can calibrate it…

Gosh, what a buy!

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