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Topic: Hysteresis and Safety in a Heater Controller (Read 5 times) previous topic - next topic

draythomp

When I first installed my arduino thermostats I hooked them up parallel to the old ones.  I ONLY ran the arduino ones when I was home and able to keep an eye on it.  I found things like having to smooth the temperature measurements much more than I expected, having to have a different hysteresis value for cooling vs heating, relay spikes on the power lines coming from the air pumps, etc.  There were things going on that I had no clue even existed.  Some things were caused by me, for example: I used the 24VAC supplied by the heat pump to power the arduino.  I had to take the rectified, filtered 24VAC that became 37VDC and reduce it to 9 volts for the arduino.  I used a nice little buck supply, but his created heat, not much, but enough to cause the temperature reading to mess up.

So, my recommendation is to parallel what ever you have now to run the system for long enough that you feel comfortable with it before you commit to the new device.
Trying to keep my house under control http://www.desert-home.com/

retrolefty

Quote
So, my recommendation is to parallel what ever you have now to run the system for long enough that you feel comfortable with it before you commit to the new device.


From a safety perspective it would be better if the arduino controlling output contacts were wired in series with the existing thermostat contacts. That would act like a redundant safety override in the event that the arduino output was stuck on or invalid. Set the existing thermostat heating setpoint higher then the desired arduino setpoint for the heating mode and set it lower then the arduino for the cooling mode. The Arduino would then be free to control the heat/cooling commands within the two existing thermostat's setpoint settings.

Lefty


draythomp

Lefty, that is actually a good idea.  I didn't think of it, so I just had them parallel and turned off the one I wanted to use.  It was a couple of weeks before I trusted the new one enough to leave the old one off overnight.  But then, I don't use flame to heat my house and the heat pumps are outside.  So, one should act accordingly.
Trying to keep my house under control http://www.desert-home.com/

bIG_dEAL

Hi Guys. Just wanted to say big thanks for all the ideas and links. Just getting into the whole Arduino platform and found this forum a real gem of information and a great source of help. Cheers!

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