Solder Smoke Fan

Some time back, I started experimenting with liquid flux to practice lead-free soldering. I got a face full of fumes that instantly cleared up my sinuses every time I tried to use it, which worried me a little since you are supposed to avoid breathing in those fumes. The package says the flux contains products known to cause cancer in California, but, hey, I’m not in California.

To get around the problem I figured I would use a desk fan I used in college to blow away the smoke, but it ended up being too powerful and cooled down my soldering iron to the point that I couldn’t melt the solder properly. After some thought I decided to build a solder smoke fan to blow away the flux fumes using an old stereo system heatsink fan I kept for just such an occasion.

The circuit idea is pretty simple. I used a 555 timer (will do a blog on this in the future) to generate a PWM signal (have done a blog on this), which I used to control the speed of the fan. The 555 timer can accept input voltages from 5V up to 18V so I figured I would use a 9V battery to power the fan, though the fan is capable of accepting up to 12V at 80 milliamps. After some early testing I figured out the fan takes about 50 milliamps at 9V with 100% duty cycle. Since the 555 timer can provide up to 200 milliamps, I chose to run the fan directly off the chip. This blog entry will focus more on the exterior build because I haven’t talked about 555 timers yet. In fact, the only thing I will say about the circuit is that I used a potentiometer (variable resistor) connected to a knob to vary the duty cycle of the drive signal for the fan, thus controlling the speed. Check out my blog entry on PWM if you don’t remember some of these terms.

When I was building the RGB cube way back in August of 2010, I tried a few different acrylic enclosures to see what they would look like. Among the rejects was a hockey puck display box typically used for storing signed pucks. I thought it would be perfect to house my fan so I used a 2” diameter hole saw to drill a hole in either side of the display. That way, air can flow in from the back of the fan and out of the front to dissipate the smoke. The fan I was using had four screw terminals in its four corners so I planned on using machine screws to hold the fan in place and ultimately to put the entire assembly together. You can see a shot of all the hardware I used in Figure 2. I was also going to leave it clear for a see-through facade.

Figure 1. Pile of Shattered Dreams

A lot of these initial plans ended up working out, but there were quite a few epic fails. Check out Figure 1 to see how many different displays I went through before I got something I could work with (about 4). The good thing is the display comes in two pieces that fit together so if you buy 2 of them u actually have 4 chances to get 2 good pieces out of the lot.  

I had initially planned on putting the 9V battery inside the enclosure itself, but, by the time I started to put all the pieces to together for one last test fit, the battery was too big for the bottom of the case. Making things fit right turned out to be my biggest problem throughout the build because I would constantly have to file out bigger holes or cut new ones. In the end, I bought some 9V battery holders (see Figure 2) and secured one to the bottom of the case using some small screws from the pack of switches I got at Radio Shack. I also elevated the fan using some standoffs – I think they were about an inch and a half. You can find all the materials I used to build the enclosure in my BOM at the end of this post. 

 Figure 2. Assorted hardware used in building the fan enclosure

I ended up changing my mind on the transparent housing scheme because there were too many noticeable scratches on the acrylic once I finished cutting out all the holes. I sanded down the face until it was smooth then painted the entire enclosure flat black to match the fan, shown in Figure 3. A knob I picked up from Electronics Goldmine (see my Hobbyist Links page) completed the exterior build.

 Figure 3. Painted hockey puck displays after drilling all the holes

Figures 4 and 5 just show some pictures of the near-final project. Even with the 9V battery removed I still had some trouble getting the circuit board to fit in correctly, but with a little hot glue it all seemed to work out. 

 Figure 4. One side of the enclosure assembly

Figure 5. Nearly finalized fan assembly with PWM circuit attached

Figure 6 is my final project, and yes it is running in the picture. A quick solder test showed that it actually worked really well. I was able to solder wires, blow away the smoke, and not lose any significant temperature on the soldering iron. I am actually glad that the battery didn’t fit and I had to elevate the fan because I think it’s a more natural position for getting rid of the smoke. Several of the connections I solder are held in place by helping hands or something similar so having a bit of reach with fan turned out to be pretty useful.

All-in-all I would say this project was a success, though not without several failures. I will do more on the circuitry I used when I talk about 555 timers, because it’s a pretty standard topology for that particular IC so look for that in the future. Comments, as usual, are always welcome.

Bill of Materials

ITEM	QTY	UNIT PRICE ($)	PRICE ($)	LOCATION
9V Battery Holder	1	2.59	2.59	Willy's Electronics
Hockey Puck Display Cube	1	2.99	2.99	The Container Store
12VDC Fan	1	12.50	12.50	PC Hub
1/8" Potentiometer Knob	1	0.40	0.40	Electronics Goldmine
SPST Heavy Duty Slide Switch	1	1.57	1.57	Radio Shack
PCB Standoffs	4	0.08	0.32	Electronics Goldmine
Set of Machine Screws	1	6.21	6.21	Home Depot
TOTAL PROJECT COST			$26.58