DIY Temperature Controlled Auto Fan V1.0

Sunday, August 16, 2009

This is the first DIY project undertake to control my saltwater aquarium’s temperature, maintaining it at around 27 degree C.

Since the room temperature is about 30 degree C, by using two DC fans, blowing on the surface of the water, is able to bring down the temperature of about 2-3 degree. Therefore there’s no need to use the much more expensive approach such as using an aquarium chiller.

However to avoid the water temperature from getting too cold during the night, a simple temperature controller is used so that the fans can be turn off when the tank temperature fall less then 27 degree C

The control circuit works on a simple 741 Opamp and a 50K Ohm thermistor and a temperature sensor. The fans are controlled by a relay that will latch on from the opamp output via a transistor,

Here’s how the project looks like,

Here are the components used

The temperature probe, made of a 50K thermistor

The DC fans, two 3 inches 12VDC fans. Commonly used in PC casing

The PCB. Stripboard type

The enclosure

The final Assembly


The Fans with holder

The complete set, inclusive of 12VDC adapter

The Calibration.

The calibration is fairly simple, I placed the probe into a warm water together with a calibrated digital thermometer. When the warm water temperature drop to 27 degree C, I turn the trimmer pot until the circuit turns on the fans. Repeat this process until and find tune the trimmer pot if the fans does not run when temperature drops below 27 degree C.

The important of temperature of a saltwater tank

Sunday, August 9, 2009

For saltwater organism to have a comfortable living environment, especially in a confine area such as a home aquarium, it is very important that the temperature of a saltwater tank be maintain as consistence as possible.

I’m living in a tropical country, with room temperature sometime goes to as high as 33 degree C during a hot sunny day and may go down to as low as 25 degree C during the night. If the saltwater aquarium temperature is not maintain at a constant degree, most of the living organism, the fishes, the corals will not able to survive such dramatic changes. Therefore some king of cooling mechanism is required.

There are basically 3 ways to cool down a saltwater tank.

  1. Use a cooling fan to cool the water surface of the tank.
  2. Use a aquarium chiller to chill down the water.
  3. Bring down the room temperature with a air conditioning unit.

Option 1 is the cheapest to setup but lack of consistency and efficiency. The amount of temperature that the cooling fans can bring down is about 2-3 degree C.

Option 2 and 3 will be more effective but expensive to setup and maintain. It is independence of any factor. Just set your desire temperature and the system will cool it to perfection. All you need to do is to pay for the high electricity bill.

After observing my setup and its environment, I use option 1 instate. Reason was room temperature is at about 30 degree C, so with the fan on, it brings down the water temperature to about 27-28 degree C. This is the desire temperature for my tank.

2nd reason is cheap to setup and low in maintenance cost. I choose to use two PC 12VDC fans for this purpose.

The downside of this system is that the saltwater aquarium water evaporates at a very high rate. I’m loosing about 5-8mm of water per day. If left unattended, I lost about 20-30mm in a week. When this happen, the salinity of the saltwater will increase and if it goes too high, it will create some unfavorable condition in the aquarium. Fishes and corals may get stress and sometime even death.

In order to overcome this problem, I decided to work in 2 areas.
  1. Use a temperature controlled fans – The cooling fans will only runs when the temperature is above 28 degree C but will stop when water temperature drops to less then 27 degree C. This helps reduce water evaporation.
  2. Introduce an automatic water top up system. This system will constantly top up the lost water due to evaporation, water salinity will be maintained.
I will now work into this 2 area with some DIY gadgets.