Help Me Design a Thermostat/Humidistat Fan Speed Controller

[moonquasar]

I'm interested in wiring my fan for two speeds - a low speed for when both temperature and humidity are below their respective set points and a high speed for when they are above their set points.

Here's a diagram to illustrate what I'm thinking. I know this has been done before in one form or another. I'm looking for a simple effective economical solution. Your feedback is appreciated.

The current diagram shows using a 5VDC PSU and 5VDC -> 120VAC relays. This could also be set up using no PSU at all and 120 -> 120VAC relays.

I was thinking of using two triacs to set the high and low speeds. Perhaps it would be just as good to set the low speed and have the high speed always at full.

Thoughts?

 

[moonquasar]

Oops, the relays are reversed. I want the N/C relay connected to the low speed controller.
That way, the fan runs at low speed until the thermostat/humidistat applies power to the relays, opening the N/C and closing the N/O.

 

[qupee]

Talk about reinventing the wheel. Why not simply purchase a controller? Such things exist...

I mean, unless your time is absolutely worthless you will spend far more trying to design your own just to end up with an untested setup that has less features than most controllers you'd find. Heck, just your sensors, relays, and two separate controllers will cost more than a decent temp-fan controller.

Also, it doesn't seem like you're totally thinking this through. Controlled by humidity? Why? What if temp is over threshold but humidity is not? You haven't addressed that scenario.. You will quickly be into programmable logic territory.

My opinion, buy something like this Grozone Temp 2V controller and be done with it. Get on with more interesting parts of life.

 

[moonquasar]

• GROZONE TV2 MULTIMODE FAN SPEED CONTROL TEMP-2V (1)
• Product code :
• 36119
  
• Retail price : $139.95
• Automatic fan speed controller with adjustable idle speed
• Built for centrifugal fans
• Low T° limit
• 55°F - 95°F (13°C - 35°C)
• Speed varies from min. to max. within 6°F (3.3°C) around setpoint
• Up to 750 W - 6 A - 120 V

It looks like a nice product but it lacks a humidistat and therefore does not fulfill the desired functionality in full. It could be coupled with a humidistat but then we're back to building the circuit again.

The price tag from this particular retailer is 139 USD. I'm hoping to have more functionality at a lower price point...

Here is a partial parts list for my controller...

• MoonQuasars Basic Parts List ($)
• 1 x 5VDC PSU @ 2A - 3
• 1 x Thermometer/Hygrometer - 40
• 2 x Power Relay (3-48VDC trigger; 10A load) - 2
• 2 x 5A fan speed controller (triac) -20
• 1 x 6" centrifugal fan @ 1A - 81

=> $65 for basic speed control components
+ $81 for a fan
=> $146

 

[rives]

You only need a single relay, with the N.C. driving your low speed and the N.O. driving the high. I haven't dealt with humidistats, but thermostats that are capable of switching line voltage usually don't have the resolution that the low voltage models have. I've built diac-triggered triac speed controls that actually perform better than commercial offerings.

 

[moonquasar]

What if temp is over threshold but humidity is not? You haven't addressed that scenario..

If either temperature or humidity are at their respective set points, the fan will switch from low speed to high speed. That is the desired functionality.

case: both temperature and humidity are low;
do: cycle air at a rate sufficient for plant respiration (low speed);

case: temperature is high and humidity is low;
do: increase ventilation - change fan speed to high;
optionally: add an ultrasonic fogger into the circuit ~ $10
(the fogger would be placed near the intake or in a lung room...)

case: temperature is low and humidity is high;
do: increase ventilation - change fan speed to high;

case: temperature is high and humidity is high;
do: increase ventilation - change fan speed to high;

 

[rives]

You might be better of with 24vac as your low voltage. Most t-stats are built to work with it, you only have a cheap, widely available transformer instead of a more elaborate power supply. DC tends to raise hell with contacts long-term.

 

[moonquasar]

You only need a single relay, with the N.C. driving your low speed and the N.O. driving the high.

Like this?

I haven't dealt with humidistats, but thermostats that are capable of switching line voltage usually don't have the resolution that the low voltage models have.

I see. The thermostat I was looking at is the ventmatix duostat - it is rated for switching line voltage. Perhaps it would be better to source both a humidistat and thermostat separately. I wonder how that would look wired up...

I've built diac-triggered triac speed controls that actually perform better than commercial offerings.

Greek to me but I'm interested in hearing more about it.

 

[moonquasar]

 

[rives]

View Image

That's better! See my comment above about using 24vac in case you missed it.

This is what I was talking about with the motor speed control - http://www.circuitstune.com/2012/01/ceiling-fan-regulator-speed-controller.html

 

[Stonefree69]

Hey rives, when I was looking for a speed control for a 12" Max fan I seemed SOOL unless I used the more expensive proprietary CAP controllers. I just went w/2 8" Valulines instead, one pulling the other pushing on inlet. Couldn't be happier. Don't know what the issue is with some of those fans, the smaller ones seem to be speed controlled easier.

I was into electric motors and EV parts/pwm controllers about 12 years ago, Lynch motors was the bomb racing small electric vehicles.

 

[rives]

I think that Can fans recommends a variac for controlling their larger fans, which is a little strange. Most motor manufacturers want you to steer clear of lowering the voltage to a motor because of the resultant increase in amperage, but you can get away with it with an inline fan because of the cooling airflow over the motor. Some motors just aren't compatible with triac-based speed controls. I am really curious to see how my new EC fan works, but I've got to get the damn thing installed first!

 

[eyes]

i would be interested in this as well. can you take pics of the parts as well as the part numbers so others can build one as well- once you get it built and working.

 

[moonquasar]

Sure thing, eyes! Sourcing components is a lot of work. I am having trouble finding the 24 volt ac transformer and relays at a competitive price to the 5 volt dc counterparts.

 

[moonquasar]

WARNING:
NOW ENTERING PROGRAMMABLE LOGIC TERRITORY!

 

[LakesideWiseman]

How did this pan out? I've got an issue where I want to use my exhaust fan as humidity control, but refuse to have it turn off completely.

I'd be happy with a retail solution, but have yet to find one that satisfies my needs. Did you ever finish with the build? Care to share share which products you used to create the relay?

 

[moonquasar]

Greetings Mr. Wiseman,
I didn't see you post until just now. No, I have not gotten to assembling this. I have acquired most of the parts that I need. I am planning to show the diagrams to an EE friend later today. Not sure when I will have time to put it all together. Will keep you all updated.
kInD Regards,
M, Quasar

 

[LakesideWiseman]

Greetings Mr. Wiseman,
I didn't see you post until just now. No, I have not gotten to assembling this. I have acquired most of the parts that I need. I am planning to show the diagrams to an EE friend later today. Not sure when I will have time to put it all together. Will keep you all updated.
kInD Regards,
M, Quasar

Thanks! Please do!