Fan Speed Controller - Will it Work?

K

Kervork

Well-Known Member

Why did I not just buy one of the $20 ready made? My plan is to desolder the variable resistor on this and replace that with a series of relays connected to different fixed resistors. Those relays are then controlled by a RPi which will hopefully be able to vary the speed from 35%, 50%, 75%, 100% by toggling the appropriate relays.

What I want is for the RPi to fire up the fan at 100% when the lights come on. Then two minutes later decrease the speed. Throughout the light cycle, vary the fan speed from low to high as needed to maintain temperature based on the readings from the temp sensor.

Could have bought a $20 fan speed controller but this was cheaper and bigger and easier to hack. If it doesn't work, no great loss.

Anyone out there ever control fan speeds using relays and resistors? Will it work? Is there a flaw in my plan?

Just in case I also bought a similar PWM controller.

Amazon.com: HiLetgo 2000W PWM AC Motor Speed Control Module Dimmer Speed Regulator 50-220V Adjustable Voltage Regulator: Home Improvement

Amazon.com: HiLetgo 2000W PWM AC Motor Speed Control Module Dimmer Speed Regulator 50-220V Adjustable Voltage Regulator: Home Improvement
www.amazon.com
 
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Beehive

Beehive

Well-Known Member
Here's a flaw. You have no way of measuring Cubic Feet per Minute.

You can adjust your blower all you want. 50%, 75%, 25%. But how much air does the blower replace and how fast?

I went from an 8" to a 6". I ran the 8" at half knob. The 6" is at full. With both fans I could find the balance of not vacuuming out the grow room atmosphere.

How much air or replacement per minute was I doing? I have zero clue because I can't measure CFM.

I now go by air freshness. Does it smell stale or fresh? Fresh like walking outside. The more flow, the happier they are.

With your figures. 30,50, 75, and 100%. How much CFM is per step? How much cfm does 30% pull? 50%? 75%, 100%?
 
K

Kervork

Well-Known Member
The air flow needed for cooling dwarfs the air flow needed by the plants to breathe. The plants will have plenty of air, I need to be able to adapt to constantly changing input air which varies by 30F over a day and 60F over a year.

An industrial HVAC economizer system will automatically inject a certain amount of fresh air based on outside temperature. Same principle.
 
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McStrats

McStrats

Well-Known Member
Kervork said:

Why did I not just buy one of the $20 ready made? My plan is to desolder the variable resistor on this and replace that with a series of relays connected to different fixed resistors. Those relays are then controlled by a RPi which will hopefully be able to vary the speed from 35%, 50%, 75%, 100% by toggling the appropriate relays.

What I want is for the RPi to fire up the fan at 100% when the lights come on. Then two minutes later decrease the speed. Throughout the light cycle, vary the fan speed from low to high as needed to maintain temperature based on the readings from the temp sensor.

Could have bought a $20 fan speed controller but this was cheaper and bigger and easier to hack. If it doesn't work, no great loss.

Anyone out there ever control fan speeds using relays and resistors? Will it work? Is there a flaw in my plan?

Just in case I also bought a similar PWM controller.

Amazon.com: HiLetgo 2000W PWM AC Motor Speed Control Module Dimmer Speed Regulator 50-220V Adjustable Voltage Regulator: Home Improvement

Amazon.com: HiLetgo 2000W PWM AC Motor Speed Control Module Dimmer Speed Regulator 50-220V Adjustable Voltage Regulator: Home Improvement
www.amazon.com
Click to expand...
Your fan speed should be based on 10-12 (ach) air changes per hour. As far as your electrical mods, a VFD should allow you to dial in the rpm of the motor.
 
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