Greetings,
I am fairly new to electronics, and have mostly worked with DC circuits so far. I have an AC fan I want to use to make a carbon filtered ventilation fan for my soldering station. I can do this with a DC circuit and DC fan, but when researching how to do it with an AC fan I came up with more questions than I started with...

The fan I have is a Nidec TA450AC model A30122-10. It is about 5x5x1.5 inches, and rated for 115VAC, 50/60Hz, .26/.21A. I found data on the fan here.

In my research so far it seems there might be three solutions: 1> Use a TRIAC/DIAC circuit, 2> Use a MOSFET circuit or 3> Use a microcontroller/PWM circuit. There seem to be benefits/drawbacks to each method, and I don't know which method to choose, or even if I'm headed in the right direction.. I don't know how to tell if the fan is single-phase, triple-phase, induction... ugh. I am looking for an inexpensive solution I can build myself, that performs well.

Can anyone help me find the right solution for my application? Or at least point me in the right direction?

Thanks much,
doval

 

Buy an electrical box and a dimmer at the hardware store. Buy a power cord or cut one off a dead appliance.
That solution keeps beginners from assembling things that run from the wall outlet, it complies with the Terms of Service for this website, and it saves me designing something that any Google search would find in a millisecond.

Edit: Five posts later I find this will not work.

 

What is the reason you want variable speed for your fan? it is most likely a shaded pole motor if so the easiest way would be a triac control.
PWM is pretty much limited to DC control.
Max.

 

@MaxHeadRoom i want variable speed control because it runs at high RPM and moves too much air for the soldering table. I just need enough airflow to suck the vapors through the carbon filter, i dont want to possibly cool the soldering iron or solder while im working.

I looked up your reference to shaded pole motor and I believe that's what it is, but is there a way to tell for sure without taking it apart? i.e could it be deduced from the information on the .pdf I linked above?

It sounds like you're suggesting the triac/diac solution is the easiest way to go? i have researched the triac/diac solution and i found 2 things: 1) comments suggested it can create a lot of noise in the motor due to the clipped waveform and 2) the circuits i found were all designed for high(er) amperage motors. I'm only using 260mA. For those two reasons I wasn't sure if triac was the way to go. what do you know about the potential noise issue? it will be close to me while im working and if it buzzes or makes annoying noise it will be an issue. Is this the best solution for a low current application like this? To be honest, I was leaning toward the triac solution (i liked this circuit ) before I posted this thread but I wanted some input on the other options I found before I made a decision to buy parts. And I've gotten good direction from the folks on this forum before.

I, too, had thought PWM solutions were for DC but I found several references regarding using a PWM/microcontroller as part of a solution for AC motor control. However, it seemed more complicated than it needs to be so I brought my questions to this forum.

Thanks again for your time and constructive comments.

Cheers
doval

 

The diac/triac circuit is what is inside a hardware store dimmer. If it buzzes, use a longer wire and place the controller a few feet away from your soldering iron. You might not need a dimmer because controlling the air flow is a perfectly good way to reduce flow across the soldering iron by misdirecting the air stream or reducing the air available at the intake side of the fan. Remember, the air speed can be altered by the size of a tube. As the tube expands, the same amount of air will flow at a lower speed. In the other direction, making a tube smaller can restrict airflow on either side of a fan, but it works better on the suction side.

 

@#12 My understanding is the noise is created by the way the triac/diac circuit works, by the clipping of the waveform during the polarity switch. I do not understand how using a longer wire will solve the buzzing in this case, can you elaborate please? Also, can you clarify what you mean by "Controlling the air flow is a perfectly good way to reduce flow across the soldering iron by misdirecting the air stream or reducing the air available at the intake side of the fan." The way I interpret this is I think you're suggesting I change the direction the fan is pointing or put a shroud over the intake or something similar. That's not what I want to do. I don't want to mess with the direction of the airstream, I need for the air to flow across the solder area to suck up the fumes. I just need to be able to control the rate of flow so I get it fast enough to pull the fumes away and through the carbon filter but not so fast that it makes it difficult to solder well.

I am looking for a circuit to build so I can design a PCB in a form factor that will fit into a fabricated case with the fan. I prefer not to have a fan with long wires to the controller wired to the mains line all spread out. This video is an example of what I'm trying to do, but with a little larger, more powerful AC fan. I've built a DC unit similar to what's in that video but it just doesn't have enough flow. I want to use the AC fan but I would like to be able to vary its speed instead of having to move the fan further away. And most importantly, it's a learning experience for me, which is the real benefit.

In my research I've found what appears to be several options that could meet my needs, I am looking for your advice on which are the most viable, best solutions. From what you and MaxHeadRoom have indicated it sounds like the triac/diac circuit is the way to go.. my only concern is the potential noise issue..

I very much appreciate you taking the time to help. I've been lurking on this site a while and finally decided to sign up and post a question because of the friendly, helpful attitudes of members like yourself that take time out of their busy day to help others learn about circuits. Thank you!

Kind Regards,
doval

 

I do not understand how using a longer wire will solve the buzzing in this case, can you elaborate please?

If you can hear the triac circuit buzzing, it is close enough for you to hear it. A longer wire will allow the triac circuit to be farther away from you and the fan.

Here's some news. I just assembled exactly what you are describing, and the fan will not run at all unless there is a significant load to allow the triac to cycle properly. When the fan does run, it only runs in the top 30% of the dimmer's range. You can't dim this fan below 70% without it acting like it's going to stall.

Your choices include:
Buy the right size fan,
Learn how to use it with only 30% dimmer range,
Use a damper or baffle to block off part of the intake area,
Use some shape of physical structure to redirect some of the air flow so it all doesn't travel across the soldering iron.

Other People might have additional ideas.

 

@#12 Ah, I see what you were saying about the length of the wire, that makes more sense now. Regarding the cut-out, I was afraid that might be the case. Do you have the specs of the gate trigger amperage from that dimmer switch? I'm curious if it's just rated for a higher amperage load. The fan's max amperage is only like 200-250mA so maybe that's why the dimmer isn't working well with the fan? I was looking at using a BT136-600 which has (if I remember correctly) a 35mA gate trigger. Maybe I'm just confused. Either way, thank you for testing the dimmer switch circuit, that was very helpful!

 

Do you have the specs of the gate trigger amperage from that dimmer switch?

It's just your standard Hardware Store light dimmer for residential use. Probably 600 watts.
Most triacs in this range of voltage use 25ma to 50ma for their gate drive. I don't think you are going to find anything you can change significantly in that area of the circuit. If you use a 10ma triac gate, it will create a circuit that is more sensitive to inductive loads (dv/dt misfire).

I think it is the inductance of the motor which refuses the fast rise in current required to pass the gate current. Placing an incandescent lamp as an additional load made it work at all, but still not well.

Here is yet another idea: Mount the fan in a box about 6 inches as a cube. Place a tube to the solder area to suck in the fumes. Cut a rather large hole in one side of the box and use a sliding cover to regulate air flow. This is called a bypass style of regulator.

 

Thats a good idea, thank you!

I have an additional question about the triac circuit, if I may.. Why does this triac circuit work with a drill as in this video, but won't work well to suit my needs with a small fan? And even if the triac circuit won't work, it seems like there has to be some (electronic circuit) solution to being able to vary the speed of a small motor like this, somehow, right? Edit: I mean, of the options I had originally questioned as potential solutions, the triac doesn't seem to be viable.. and the PWM solution appears to only be viable for a three-phase AC motor. So the only other option I am aware of is using a MOSFET circuit. But I've only done preliminary research on this solution, is this something you can comment on/have experience with?

Thanks again

 

The hand tool application operates on a different motor technology, Universal motor rather than induction.
1ph induction motors are notoriously bad for rpm control, the smaller types such as yours uses what is known as shaded pole to obtain the split phase, as opposed to larger types that use a phase shift capacitor.
The capacitor types can drop out of run when loaded at low rpm, unlike their 3ph cousins that allow precise control.
Max.

 

@MaxHeadRoom Yeah, that's what I'm finding out. There doesn't seem to be a good solution for my particular application other than what #12 has suggested.

Research update..

So it seems my earlier research suggesting PWM control is only viable for a three-phase AC motor was not accurate. Apparrently there is a way to use PWM to drive a single phase AC motor. I found a number of references to a solution like this:

"You can use PWM but you would also use an H bridge setup which requires four transistors. You then PWM the transistors in the H bridge and that gives the motor the correct average voltage and the correct frequency. The input gets rectified and filtered into DC, then the DC gets chopped up into a pseudo sine (or special pulse width). This is the essence of a transformerless output controllable frequency drive."

Interestingly, I found this video that shows a breadboarded PIC/PWM circuit used to vary the speed of a single phase shaded pole motor. It's a larger motor than I have, though. But theoretically the PIC/PWM solution could work. I do have many of the parts already and am familiar with programming the Atmega328. Any comments?

 

Here's another PIC based controller, and with a fan that's very close to what I have...

 

Interestingly, I found this video that shows a breadboarded PIC/PWM circuit used to vary the speed of a single phase shaded pole motor. It's a larger motor than I have, though. But theoretically the PIC/PWM solution could work. Any comments?

That video appears to demonstrate phase angle control, not PWM?
See also Fairchild AN-3006 for details on this type of control using a IC which could also be translated over to a PIC etc.
Max.

 

I have read about the AN-3006 here, but wasn't sure how it was used. I saw the ICs in his implementation and assummed it was PIC/PWM. Thanks for the heads up.

 

So for the AN-3006, it looks like they're using a 555 timer circuit to control the frequency and a triac for the current control? Is that correct? Wouldn't you still run into motor noise issues? I've seen some triac implementations that cause a horrible buzzing in the motor. That you tube example didn't seem to have any audible noise.

 

Phase angle control itself is pretty much non-tailorable on the output once the triac has fired, the 555 was used to synchonize the firing pulse with the zero crossing opto detector circuit and the firing pulse on the 555 output.,
Max.