Understanding Dimming Thermostats

Understanding Dimming Thermostats

Choosing the correct thermostat is essential to creating the perfect environment for reptiles in captivity, In this article i will explain how the dimming thermostat works and how to use it correctly. 

first of all lets look at the dimming thermostat, its a box, you plug it into the wall socket, you plug your heater into the thermostat and there is a probe on the end of a wire that measures the temperature, and a dial on the box that allows you to set your desired temperature. 

A dimming thermostat controls the temperature by measuring the temperature at the probe and comparing it to what has been set on the dial, it then increases or decreases the power flowing to the heater accordingly.  For example if the temp at the probe is below the set temp on the dial, it will increase the power, and if you have a spot lamp plugged in as your heater it will make the spot lamp brighter and output more heat. And the opposite is true that if the temp at the probe is higher than set at the dial it will reduce the power to the heater which would make the bulb dimmer and less heat would be output. The Dimming thermostat continuously monitors the temperature at the probe and make makes tiny adjustments up and down in power output to ensure the heat lamp is always at the correct temperature. 

How to correctly use a dimming thermostat:  Always make sure your heater is set up at one end of the enclosure if in a terrestrial enclosure or at the top of an arboreal enclosure, this ensures you have a hot end and a cool end, its vital your pet reptile can escape from the heat once it has reached its optimum temperature.  Next the thermostat probe needs to be positioned close to the heater usually between the heater and the cold end.  Set your species desired basking temperature on the dial, plug the heater into the thermostat, plug the thermostat into the mains and switch on.  You now want to leave the enclosure to heat up, once the temperature is near you should notice the bulb start to dim slightly once the desired temperature has been reached, use a thermometer ideally an infra red hand held thermometer to verify that the basking area temperature is indeed at the correct temperature. 


Your species needs a bright basking area, but the thermostat dims it down so much when its at temp it doesn't light up? 

Ok, this means you are using a basking bulb that is too high wattage, its simply giving out too much power for your size of enclosure, you should always use the lowest wattage bulb possible to achieve your desired temperature. For example you have a 2ft vivarium, if you use a 150W basking lamp, it will heat the enclosure rapidly and the thermostat will only have to allow a small amount of power through to maintain your basking temperature, your lamp will never be bright. 

On the other side of things, if you only use a 10W basking lamp in your 2ft vivarium,  the enclosure may never reach your desired basking temperature and the spot lamp will be always fully on and never hot enough. You may need to experiment with wattages until you reach the sweet spot, ideally the thermostat should only need to deliver 80% of full power to your heat lamp to maintain the desired temperature, this allows the bulb to be visibly bright and have capacity to increase the temperature if required, but in the extremely unlikely event of a thermostat failure the enclosure should not overheat dangerously  

The thermostat is not controlling the heat lamp!

Whenever i have heard this complaint , with a brand new thermostat, it has always, always been a case that the heatlamp has simply not been plugged into the thermostat! the heat lamp must be plugged into the thermostat for it to be controlled by it!

The thermostat is dead!

There are two fuses on a thermostat, one in the mains plug, which should be fitted with the lowest fuse possible for safety, never use a 13 amp fuse in your vivarium electronics, I always prefer to use a 3 amp fuse or lower, it does mean that sometimes when a bulb "blows" it takes the fuse out with it but i would rather that then have an electrical issue and not have a fuse blow. The second fuse is a quick blow fuse, located in the case of the thermostat, these are designed to protect the circuitry inside the thermostat in the event of a bulb failure. its always handy to have some spare as they do tend to go when a bulb fails.