Mask Fans with Speed Control.

[Jaan]

OKay, Like many of you I wear eyeglasses, which can (will) fog up. So far my fan modifications have worked very well for me. This project was my solution and hopefully some of you will find things here you can use.

I have a stock JT mask fan but it has a couple of design flaws which really annoyed me. Since the fan was only on one side, and it was a wimpy fan at that, only one side of my eyeglasses would be clear. The other thing was that the battery was internal and you had to remove the entire unit to change the single battery. Anyone who has changed one of these JT mask fans knows taking it on and off is a serious pain in the ... fingers.

I decided to upgrade it all. I figured that 2 big fans, running slowly, would move a lot of air and be quiet as well (which turned out to be the case). One of the problems with muffin fans is that they require a certain voltage or they wont turn. What you need is an actual speed control circuit. Luckily such circuits are quite common. What I used is a circuit called a "Pulse Width Modulator". If you Google that you'll find lots of different designs. Basically, it's like turning a power switch on and off over and over. The faster you turn it on and off, the faster the motors, or fans, will spin.

(EDIT: I should mention that when you're figuring out how much juice the fans will draw, you need to factor in what the duty cycle of the Pulse Width Modulator is. If you figure how much the fans draw when going all out at 100% without a speed control, than if the PWM was set to 50% the circuit will draw a little more than 50% ... since nothing is 100% efficient.)

Originally I was going to build mine from scratch, but when I was ordering parts from All Electronics I ran across a circuit with board and parts for only $3.50:

Speed Control Circuit

I ordered the other parts I needed for this project from them too ... mainly the fans. I ordered both 25mm and 20mm fans. At $4 ish a piece, what the hell. All Electronics is cheap. All the parts I used in the project only cost me about $15.

(Oh, by the way, if you do something like this, unless you want to spend 3 - 5 times the money, don't go to Radio Shack. Yesterdays technology at tomorrows prices.)

I used the biggest fans I could shoehorn in. I used the 25mm fans and I had to do a lot of dremeling to get enough material off to fit them in. If I did this project again, I'd probably use the 20mm fans since they'll fit no problem. I also use an external battery pack now so I don't have to take my entire mask apart to change batteries.

K, down to the short strokes ...

Step 1: Build the circuit and an enclosure

Pretty straightforward, solder all the parts to the board and lay them down so they can fit inside a small box;



The speed of the fans is controlled by that small trim pot you see the tool turning. You can easily substitute an external trim pot (think volume knob) so you can change the speed of the fans on the fly. I wanted to make it as small as possible though, and so far it hasn't been a problem. However, if you do it my way you might want to use the proper plastic tool ...



... so you don't short out anything.

For the enclosure I built my own from sheet plastic you get at model stores. Very easy to use and responds well to heat, and glues well. I made a template out of paper, then cut out the form from the plastic sheet with scissors;



To get the sharp bends I scored one side with a soldering iron, and then used heat on the other side as I was bending it;



All in all it came out pretty good ... although I have to admit I did it twice to get it just right. If you don't do it right you'll break the plastic at the seams.

Mount the board in the box;



Hot glue it all up and use a zip tie to keep the wires from being pulled out;



Solder it to a battery pack and glue it all up;



Step 2: Mounting Fans Inside The Housing

As I stated before, in order to fit 25mm fans inside a stock JT housing you have to shave off plastic from all over the place. I had to belt sand off two corners from each fan ...




... and also dremel off plastic from the housing itself. Whoever made the housings for JT was lousy ... the thickness of the plastic varied greatly everywhere. Luckily you can use the amount of light you can see through the plastic to tell how thick the plastic is when you're grinding it off. If you do it my way and decide to paint it another color, shave off the plastic first before painting it.

[Jaan]

I mounted the fans to the back plate with double sided 3M tape;



(This tape is VERY expensive, but it's great to have around. It's used to stick trim onto cars. I used it to years ago to mount surround sound speakers to my TV and to mount a 12 disk CD changer to the back wall of my truck. It sticks like crazy)

Trimmed it up a little;



Screwed it into the housing (you can see all the dremel marks);



And finally super and hot glued it all to make it air tight;



One of the things I wanted to do to make the fans quiet is to keep them up as far away from the top of the mask as I could. Also, the reason I made it air tight is to separate the area the masks draw air from, from the exhaust. As they sit now the fans are not touching the top of the mask at all, and draw air from as large an area as possible.

(By the way, between the double sided tape, super glue, and hot glue, this is all incredibly strong. Did I mention that I want to avoid taking this off?)

Here is a picture showing the difference between a 25mm fan and a 20mm fan. As you can see, the 20m fans would fit no problemo;

[Jaan]

Step 3: Mounting To The Mask

The rest is pretty easy. Mount the fan unit to the mask;



Solder it to the battery pack and speed control. Put an old sock over it;



Use some Velcro straps to attach the battery pack unit to the mask;




Use a couple of zip ties to tidy things up;



And there you have it;



Voila!

[omegaredghost]

just an idea what if you could hook up a heart moineter or heart beat counter to a fan. it slows down and speeds up with you. when youre sitting still looking to ambush it wouldnt be on and when youre running from the guys you tryed to ambush no fog maybe ive taken one to many to the head

[Jaan]

I thought about something along those lines as well ... only with a moisture sensor. It wouldn't be that difficult to set up, the speed is controlled by a variable resistor, as long as you could come up with a system that reduces resistance as moisture increases so the fans speed up, you're all set. Well, maybe. Success would depend on a number of additional factors, such as how quickly a moisture sensor could react to current conditions.

It would be a similar system that some computer fans have ... as the temperature increases the fan speed increases. I've installed a couple of those fans into computers myself, and they're notoriously inaccurate.

As it is now, you could easily put an external knob to control speed. I'm a woodsball player, it wouldn't be too much of a hassle to just reach up and turn up the speed as needed. That could also be the power on switch as well.

I consider this version a working prototype by the way. Next winter I'll probably make a more compact version where the speed control is inside the fan shroud.