DIY spray booth fan/blower advice

[nuno81291]

https://www.amazon.com/iPower-Inline-Ventilation-Exhaust-Grounded/dp/B009LCEUEK/ref=mp_s_a_1_12?ie=UTF8&qid=1543512189&sr=8-12&pi=AC_SX236_SY340_QL65&keywords=dayton+blower+fan

It appears these style fans would be appropriate. What I like is they can have a variable speed, unlike the Dayton centrifugal blowers which seem to be non variable.

Edit: it appears there are variable speed blowers and I am looking at the wrong ones.
 
I figure if I make the move to acrylics and an airbrush then this is a non issue. I do like the idea of being able to control the speed of the fan. It appears a similar CFM rated blower is atleast twice as expensive.

Any thoughts? Get this and an airbrush setup and don’t worry about it? Would like to move away from the dullcote rattlecans which have been hit or miss for me as far as over application goes. Time to look into airbrushes and compressors. Too bad I don’t have a garage I could run my large construction compressors in.

[MK]

Your large construction compressor may not be oil less.

[Philip H]

Any thoughts? Get this and an airbrush setup and don’t worry about it? Would like to move away from the dullcote rattlecans which have been hit or miss for me as far as over application goes. Time to look into airbrushes and compressors. Too bad I don’t have a garage I could run my large construction compressors in.

I am NOT an engineer.  This is NOT professional or legal advice.

At the risk of sounding repetitive - use what you have, vent straight outside and move on. It is VERY unlikely that you would ever have enough concentration or volume of volatile vapors from your solvent based hobby paints (even in the Dullcoat rattle cans) to create explosive risk. Not impossible, but VERY unlikely. Even IF you could create that much vapor, the mere fact of moving air around and through it means the concentration would decrease quickly enough that any resultant explosion would be starting but unlikely to harm or cause fire (especially since the MSDS says it evaporates as fast as Ether - which is pretty fast in unmoving air and really fast in moving air).  Its just not that big a deal chemically.  Now spray six or 8 cans fully into a closed blower and hit the On switch and you might well get something spectacular.

As I said up thread - a lot of this concern about fans in ducts sparking things comes from people who don't understand vapor chemistry or ignition probabilities.  Hobbiests have been building fume extraction hoods out of all sorts of things for decades.  To my  knowledge there have been none killed in explosions.

[nuno81291]

Your large construction compressor may not be oil less.

Regardless of what it is, it is far too loud for my use without being in a separate space (which I don’t have). Very handy for all my air tools however

Seems the desktop hobby oriented ones are far more bearable.

And to PhilipH; you are completely right I think I am overthinking all of this... time to get it over with so I can get back to modelling. Funny how things can grind to a halt without a way to paint/clear coat.

Thanks!

[MK]

If it's used for your air tools, most likely it is an oiled compressor and therefore not good for airbrushing.

[peteski]

The RPMs of any AC induction motor (which is what most) air-movers use depends on the frequency of the AC power running them (60Hz) and also somewhat on the load the are driving.  To change their RPMs, the frequency of their power needs to change. (lower frequency to slow them down).  That circuitry is rather pricey.  Another alternate way to give them limited speed control range is by using multiple windings on the motor. Again, that will increase the motor's cost.  Example of that are typical household fans which have buttons for LO-MED-HI speeds. Those engage different winding in specially designed AC induction motors.

[nuno81291]

So then Pete (since you are an extremely knowledgeable fellow), could you explain to me how the in-line fan I posted a link to can be controlled with a unit like this:

https://www.amazon.com/iPower-Exhaust-Controller-Adjuster-Inline/dp/B0714FFG4F/ref=pd_aw_lpo_86_lp_img_3?_encoding=UTF8&psc=1&refRID=1MDBQDEYGZGD1F2N9M4W

I have used similar “dimmers”, I will call it that because it seems to respond almost in a linear fashion (maybe my misperception), not 3 hard and fast speed steps. I use these fans and dimmers to discharge HID lighting for a decade or so now without issue. Are you saying an in-line fan such as the ones I am mentioning have multiple windings? I get the idea of what your saying, and certainly think being able to control the CFM of the fan or blower for the booth would be a desirable feature. Then again  my previous method of winter painting was in my old garage with the door open and a simple box fan to help dissipate the fumes from the spray bombs. Not having a dedicated paint space is a drag!

[peteski]

So then Pete (since you are an extremely knowledgeable fellow), could you explain to me how the in-line fan I posted a link to can be controlled with a unit like this:

https://www.amazon.com/iPower-Exhaust-Controller-Adjuster-Inline/dp/B0714FFG4F/ref=pd_aw_lpo_86_lp_img_3?_encoding=UTF8&psc=1&refRID=1MDBQDEYGZGD1F2N9M4W

I have used similar “dimmers”, I will call it that because it seems to respond almost in a linear fashion (maybe my misperception), not 3 hard and fast speed steps. I use these fans and dimmers to discharge HID lighting for a decade or so now without issue. Are you saying an in-line fan such as the ones I am mentioning have multiple windings? I get the idea of what your saying, and certainly think being able to control the CFM of the fan or blower for the booth would be a desirable feature. Then again  my previous method of winter painting was in my old garage with the door open and a simple box fan to help dissipate the fumes from the spray bombs. Not having a dedicated paint space is a drag!

Look at the specs:  This controller is not suitable for Shaded Pole Motor and Brushless Motor Fan
That is your answer. Shaded Pole is another name for induction motors.  The descriptions of many Amazon items are often very vague or incorrect. 

Well, you can somewhat "fudge" speed control to induction motors by lowering the voltage you feed to them, but that gives you very limited range of speed control. That item on Ebay is simply a type of a dimmer switch placed in a plastic box.  It might have some additional circuitry to better handle inductive loads (which is what motors are since they all have some sort of electromagnet, or a coil of wire) in them. It would likely be acceptable to control the AC motors with brushes (like a handheld drill or a Dremel tool).

I see that they recommend that controller for a duct fan which to me looks like it uses an induction (shaded pole) motor.  So they are contradicting themselves with the statement that this speed controller is not for shaded pole motors. Like I said, you can have some control over it by simply lowering the voltage. It works because the motor will simply generate less torque with lower voltage and that will slow it down when loaded by a fan blade pushing the air.  Feel free to order it and give it a try.

Here is a good write up about those shaded pole fan motors.  https://en.wikipedia.org/wiki/Shaded-pole_motor  They do include Triac-based (dimmer) controllers for that motor.  So yes, it is an acceptable form of controlling their speed.  Clear as mud.

As I mentioned earlier, the "real" way to control RPMs of AC induction motors is to control the frequency of the power being feed to them. There are probably controllers to do that, but the are likely expensive.

Search the web and read few answers:
https://duckduckgo.com/?q=controlling+speed+of+shaded+pole+motor&t=h_&ia=web

[nuno81291]

I own two of those in-line fans and each is on a similar dimmer to the one I posted. It does work. Surprised to see the description contradict itself but these are commonly sold with these style fans for exhausting heat from “indoor hydroponic gardening”. that Wikipedia link was a good read, plenty of stuff over my head...  thanks for the detailed response.

[reinhardtjh]

I'm clueless about AC motors.  The Amazon listing links to a "User's Guide" for the fan unit.  Inside that it says the motor is an "external rotor motor".  Also given is a wiring diagram and a chart showing power input and corresponding CFM output for different models.

[peteski]

I'm clueless about AC motors.  The Amazon listing links to a "User's Guide" for the fan unit.  Inside that it says the motor is an "external rotor motor".  Also given is a wiring diagram and a chart showing power input and corresponding CFM output for different models.

It is an AC motor which uses an external capacitor. This is explained in the Wikipedia "AC motor" article I linked to earlier in this thread. Just go down to the "Capacitor start motor" section.  Basically, the capacitor circuit is used to get more starting torque.  The motor's specs should list the required specifications for that capacitor.  I suspect that the starting capacitor comes preinstalled when you buy the fan unit. You just need to hook it up black and blue wires to your 120V AC power at home, and the green/yellow to ground.

[nuno81291]

Well I ordered a blower; Dayton 1tdt2 rated at 549 cfm. Price wasn’t too bad. Figure if I’m going to use some spray bombs until I get an airbrush rig I may as well go for what seems to be the best recommended fan design. Now to explore the world of airbrush and compressors. The peace of mind of the motor being out of the airstream was worth the $$$ upcharge from my in-line fans, with a bit higher cfm rating to boot. I will follow up in this thread with my booth build and impressions. Glad to hopefully not have to step out in the cold to quickly shoot a model here and there.

[nuno81291]

Do any booth owners diy or purchased have any opinion about this style booth:

https://vent-works.com/blogs/the-ventilation-blog/15945741-diy-hobby-spray-booth

I was intending to more or less build this design. Not sure if all that space behind the filter is necessary?

[nuno81291]

So my booth is coming along:


Using a piece of glass on top for lighting.

However; I wired up my blower out of excitement and was surprised by how not impressive 549 cfm feels/sounds. My I line 440cfms sound like a mini hurricane, and put off quite a strong pressure if you stand in front. This blower didn’t quite seem to be half as strong. Would this be because it was a freestanding test and not connected to ducting and the booth? No idea on the physics behind this one but something seems not quite right.

[MK]

Bernoulli's equation.  It'll feel stronger and faster once you duct it.