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Old 11-26-2017, 07:12 PM   #2
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Join Date: Nov 2008
City & State: Madison, IN
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Line Voltage: 120VAC 60Hz
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Default Re: Looked at new thermostats, nah I'll DIY this

Nice. Have you studied control systems before?

You might want to look up Two-Position controls for tuning in your controls. That way you can get it properly "damped", underdamped will be too slow to react, overdamped will be unstable (and will overshoot, causing unnecessary switching on/off which will wear out your relays). Two position controls aren't too bad to engineer; "two position" refers to that there are two positions in use ("on" and "off"). If you wanted to get fancy with it (which would mean slightly more complex controls engineering), you could have a mode to control the AC and heat at the same time, which would be a three-position control system. Just be glad it isn't like some modern commerical boilers which are variable output, which require a PID control system to utilize. My college had one of these installed (after the 3 year old non-variable one fried a lot due to switching on/off too much) and this was one of the things showed to me in my control theory (controls engineering) class.

Have fun with it.

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