Remote thermostat, AC unit is running all the time - Electronic Circuits Projects Diagrams Free

mramos1 · 31st May 2008, 08:39 PM

We have a couple AC units that run all the time (in a commercial building).

The thermostats are near the heat pumps (where the AC people say they should be) but that same area has an electrical room. The transformers in the electrical room seem to heat the area so the AC never cuts off. And the hallways are always too cold and costing money.

My thought was to make a board with a thermistor/pot/voltage divider via op-amp to power a transistor and relay to put in the hallway. The relay would open and close the thermal metal switch in the thermostat. Basically it will open and close the always closed switch as it seem to never open up. A remote thermostat to control the real one. I priced doing it the right way and it was a bit high.

Anyone have any thoughts. A better way, will there be a debounce type issue with the thermistor and pot that will bias the voltage divider on the op-amp. Do not want the relay to oscillate.

Using a uC would be my way out, but then I have to drop the 24vac to 5vdc and cost goes up. Also coding time. But not opposed to it.

blueroomelectronics · 2nd June 2008, 12:26 PM

Take a look at the DS1620, the hi & low setpoints are stored in NVRAM. You don't need any MPU once it's programmed.

mramos1 · 2nd June 2008, 02:08 PM

Quote:

Originally Posted by blueroomelectronics

Take a look at the DS1620, the hi & low setpoints are stored in NVRAM. You don't need any MPU once it's programmed.

I will take a look. I was going to use an 8 pin PIC and thermistor and delays, but that looks like a better solution if the price is right and not a pain to program the set points. Will pull the PDF and see.

I have the PICs thought.. haha..

Thanks Bill..

blueroomelectronics · 2nd June 2008, 03:40 PM

The DS1620 is I2C, I think there is also an SPI version.

rjvh · 3rd June 2008, 07:55 AM

why not puting the thermostath in the room/area that you want to control
if the aircon people say this is the best place but don't take in considration of the site situation (happens way to often) you will get these kind of problems
i've seen it more than once
Robert-Jan

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31st May 2008, 08:39 PM	(permalink)
mramos1	Remote thermostat, AC unit is running all the time We have a couple AC units that run all the time (in a commercial building). The thermostats are near the heat pumps (where the AC people say they should be) but that same area has an electrical room. The transformers in the electrical room seem to heat the area so the AC never cuts off. And the hallways are always too cold and costing money. My thought was to make a board with a thermistor/pot/voltage divider via op-amp to power a transistor and relay to put in the hallway. The relay would open and close the thermal metal switch in the thermostat. Basically it will open and close the always closed switch as it seem to never open up. A remote thermostat to control the real one. I priced doing it the right way and it was a bit high. Anyone have any thoughts. A better way, will there be a debounce type issue with the thermistor and pot that will bias the voltage divider on the op-amp. Do not want the relay to oscillate. Using a uC would be my way out, but then I have to drop the 24vac to 5vdc and cost goes up. Also coding time. But not opposed to it.

2nd June 2008, 12:26 PM	(permalink)
blueroomelectronics	Take a look at the DS1620, the hi & low setpoints are stored in NVRAM. You don't need any MPU once it's programmed. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

2nd June 2008, 03:40 PM	(permalink)
blueroomelectronics	The DS1620 is I2C, I think there is also an SPI version. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

3rd June 2008, 07:55 AM	(permalink)
rjvh	why not puting the thermostath in the room/area that you want to control if the aircon people say this is the best place but don't take in considration of the site situation (happens way to often) you will get these kind of problems i've seen it more than once Robert-Jan