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joako
Premium
join:2000-09-07
/dev/null
kudos:6

Airflow relay

Of course it's possible but is it feasible? I wish to have a box fan turn off when the A/C is turned on and then turn back on after X minutes from it turning off. What sort of sensor could be used to detect the flow of air?
--
PRescott7-2097



tschmidt
Premium,MVM
join:2000-11-12
Milford, NH
kudos:9

1 recommendation

Stick a flat vane on a micro-switch and hang it in the duct.

Rather then messing around detecting air flow why not simply sense when the AC is on. Then rig up a timer to turn off the fan for the desired amount of time.

/tom


lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
reply to joako

It is easy to keep track of the temperature over time at some vent with a microcontroller based solution. You will know when A/C has kicked in by a relatively sharp drop. When the A/C turns off, the temp will rise more slowly.



cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to joako

Use a small microphone?


lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
reply to joako

Analog idea ... maybe use a simple op-amp based circuit with 2 matched NTC/PTC resistors at the inputs? One resistor will be directly in the air flow and the difference in temperature (and hence voltage) between the two will trigger the relay.



IhatemyISP
MM1 Corbski
Premium
join:2003-01-27
Hampton, VA
reply to joako

What tom said.


James_C

join:2007-08-03
Florence, KY

1 recommendation

reply to joako

The same thermostat that turns the air conditioning on can energize a normally closed relay to turn off the fan's AC power supply... if the location of the fan vs thermostat isn't a factor, or for that matter you could get possibly close enough to the goal to just use a 2nd thermostat that shuts the fan off via relay when the temperature climbs high enough that the A/C turns on.

However, I wonder if there is another option. A breeze from the fan should make you feel cooler at any particular temperature, so by leaving the fan on while A/C is running you might have the same comfort level while using less power by having the A/C set to a little bit higher temperature.



joako
Premium
join:2000-09-07
/dev/null
kudos:6

The problem is I don't have access to the thermostat... otherwise I would just leave it running constantly and that would be the end of it.

I have a fan that blows air out of the room and into the ceiling. The issue is when the A/C is running the cold air is basically being blown right out of the room again.

What exactly is a flat vane and where would I buy one?
--
PRescott7-2097



SparkChaser
Premium
join:2000-06-06
Downingtown, PA
kudos:3
Reviews:
·Verizon FiOS

1 recommendation

I think Tom is referring to something like this. You have to add something to the tip of the actuator to provide resistance to the air flow. There used to be a type that had a side rotary actuation but I can't find it.




»www.digikey.com/product-detail/e···ND/91054
--
"Facts do not cease to exist because they are ignored." - Aldous Huxley

"When a true genius appears in the world, you may know him by this sign, that the dunces are all in confederacy against him." Jonathan Swift


tschmidt
Premium,MVM
join:2000-11-12
Milford, NH
kudos:9
Reviews:
·G4 Communications
·Fairpoint Commun..
·Hollis Hosting

Exactly, need to use a micro switch that does not require much in the way of force to actuate it. The portion in the air stream needs to be large enough to to generate enough force to actuate the switch.

Another option would be to use an optointerrupter and use the vane to break the light beam.

I did a quick check on eBay but could not find any cheap switches.

/tom


lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1

1 recommendation

Vane air flow sensor for HVAC:
»www.lowpressure.com/products/103.html

A horizontal vane could flap up and down in the air flow and turn the micro switch on and off.


neonhomer
KK4BFN
Premium
join:2004-01-27
Edgewater, FL
reply to joako

»www.kele.com/pressure/afs-series.aspx

You monitor the duct pressure. When the pressure drops out, you start the fan.

Then you can use a RIB to control the fan.... »www.kele.com/relays-and-contacto···web.aspx