Explain to me how to use a temperature controller

[Yoda466]

Sorry if this is a stupid question. I have read around online and am a bit confused. About a year ago I had an Aqueon heater go on run away. Not sure how long, but by the time I realized it my tank was at about 92 F. I know there are temperature/heater controllers that can be used along with a heater. I have never used one. When using one, do you still use the thermostat on the heater and use the controller as a backup? That seems the most sensible to me as you then have two thermostats in play with one backing up the other. However I read on one site that they recommend to set the heater to its highest setting and let the controller cycle the heater on/off. Sure that would work, but unless the electronics in the controller are significantly more reliable than in the heater have I really gained much? And even if I feel confident in the reliability of the controller, is not a "belts and suspenders" approach better? So, can I use one like this:

Let's say that I want a tank temp of 84. So I use the heater alone for a few days until I am confident that it is adjusted and holding at about 84. I then plug it into the controller and set the high temp on the controller to 86. Now if the heater goes on run away the controller will shut it off at 86. Is there also a low temp alarm on the controller that I could set for say 82 to alarm me if the heater dies?

[rickztahone]

Sorry if this is a stupid question. I have read around online and am a bit confused. About a year ago I had an Aqueon heater go on run away. Not sure how long, but by the time I realized it my tank was at about 92 F. I know there are temperature/heater controllers that can be used along with a heater. I have never used one. When using one, do you still use the thermostat on the heater and use the controller as a backup? That seems the most sensible to me as you then have two thermostats in play with one backing up the other. However I read on one site that they recommend to set the heater to its highest setting and let the controller cycle the heater on/off. Sure that would work, but unless the electronics in the controller are significantly more reliable than in the heater have I really gained much? And even if I feel confident in the reliability of the controller, is not a "belts and suspenders" approach better? So, can I use one like this:

Let's say that I want a tank temp of 84. So I use the heater alone for a few days until I am confident that it is adjusted and holding at about 84. I then plug it into the controller and set the high temp on the controller to 86. Now if the heater goes on run away the controller will shut it off at 86. Is there also a low temp alarm on the controller that I could set for say 82 to alarm me if the heater dies?

You don't want to set the heater to its max. You want to set it to a few degrees hotter than your desired temp. The controller will shut it off and on regardless and if for whatever reason the controller fails, the heater will work like normal but the tank will be running a little hotter which should be an indicator to you.

Edit: have you seen this thread?
http://forum.simplydiscus.com/showthread.php?117110-20-00-Controller-how-to-wiring-(easy)

[Yoda466]

Thanks for that. So in that case the thermostat in the heater is the backup. That would be good as well. I did see the other thread but was not thinking of a DIY approach. Looks pretty simple though. I will give that another look. Thanks for the help.