I am working on a small project that uses fans with filters for ventilation and improving indoor air quality.

I’m looking at different fan types. Is there any reason to use an AC fan instead of a DC fan? Are there any advantages to them?

 

Yes if powered directly by the AC, no power transformation needed. Hence less circuitry more efficiency and reliability.

 

@BobTPH, What happens if you want to control the speed or switch it on/off using a wifi controller.

 

then you do need additional hardware... most small fans are DC, and are easy to control the speed. but you are going to need a lot of them to have noticeable effect on the room sized spaces.

 

Ok, if I understood it correctly AC fan for the same size would be more powerful?

It is fairly easy to control the AC using a Relay/ SSR, but how could I change the speed of the AC?

I will need to use an AC/DC transformer for my other circuits e.g. WIFI module,

 

it comes down to type of motor. there are variable speed AC fans. often they will have multiple windings that need to be switched. or if you like make your own using DC motor. controlling speed of single speed AC motors means altering frequency. that means using converter. not sure what your budget or specs are. (noise, air flow, minimum speed, maximum speed etc). one of the problems with changing speeds this way is that motor may not get sufficient cooling at lower RPMs. so start with some specs and numbers...

 

I am still researching spec, but air flow and noise would be the most important.

DC fans can be controlled with PWM.

 

Many household-style cooling fans, on-a-stand, ceiling-mounted, etc., can be controlled with the Triac-controlled room switch version.

 

Great, so I need to create a Triac Circuit? But do I need to make sure the fan is compatible with the dimmer

 

Great, so I need to create a Triac Circuit? But do I need to make sure the fan is compatible with the dimmer

Yes, which means the triac must be rated for more current than the fan will use.

I would use triac based opto-coupled SSRs and implement the phase control dimmer in software. Some SSR’s have a zero cross output, which you can use in the software.

 

Yes, I am aware some triacs and relays have a Zerocross.

So if I am correct, I am simply outputting a PWM signal controlling the fan.

 

I recall a fan was needed for a shed. The CFM and Watts were approximated.
These numbers were checked and rechecked then a solar powered DC fan was installed.
Later the owner wanted to run the fan after sunset.
In this case a circuit was needed. A step down AC to DC converter module worked.

After the insulation was installed the project was considered a success.

 

Yes, I am aware some triacs and relays have a Zerocross.

So if I am correct, I am simply outputting a PWM signal controlling the fan.

The Triac is phase angle control, not PWM.
I suggest you download the Fairchild App notes AN-3006 for info and circuits.
Use a zero-crossing style of Triac, as the paper suggests.
BTW, the capacitor start/run fan version is superior to the shaded pole versions in operation efficiency.

 

Many household-style cooling fans, on-a-stand, ceiling-mounted, etc., can be controlled with the Triac-controlled room switch version.

But beware, I have had a problem with such controllers causing a audible buzz from the fan.

 

Eliora Ceiling Fan without Light,
60 Inch Wood Ceiling Fan no Light
with Remote Wall Switch,
Outdoor Fan for Patio, Porch, Bedroom,
6 Speed, Quiet DC Motor,
ETL Listed-Deep Walnut

 

But beware, I have had a problem with such controllers causing a audible buzz from the fan.

Depending on how well your hearing is, it probably will be unacceptably loud buzzing if this fan will be in close proximity to living spaces and people.