DIY flux fume filter

[georges80]

So, I've been using a commercial bench filter/fan device for several years. It uses an carbon impregnated filter element and basically draws fumes away from your face etc.

It works, but the filters are rather expensive and it does take bench space and also gets in the way.

Every so often I look at filter units that have a hose but they are quite spendy and so I end up passing. Then a couple of weeks ago I ran out of filter elements for my bench unit so revisited the hose based units - still spendy but noticed that a few commercial units mentioned locline. I've used the small locline in the past, but never noticed they have large stuff too.

Went on the hunt and found the big locline and bought 4' worth of segments and also a rectangular duct opening for it and a end 'fitting'. I then ordered a dual ball bearing 120mm 12V fan and also a few sq feet of carbon filter material (ebay).

Once I received the parts I experimented to see how I would do speed control of the fan. Initial tests with a FET driven from a function generator showed things would work well with the PWM running at around 15KHz and varying the duty cycle. At that frequency the fan ran smoothly without any 'audible' noises due to the PWM.

I then took one of my small linear LED drivers and modified the hardware to use the power FET as a pure PWM output and modified the firmware to give me the choice of 8 speeds from slow to flat out. I have found that around 1/10 duty cycle is quite sufficient when I'm soldering.

Here's some pictures. First one shows the finished unit mounted to the side of the wire shelves. The nice thing with the locline is that you can adjust its position/height etc and it stays put. Easy to move close to the soldering area and then move it back out of the way when finished. Since it doesn't sit on the bench it takes up no room and doesn't get in the way when soldering/reworking larger boards.



The filter box is made from some 1/4" mdf. Picture of the 'outlet' of the filter box that contains the fan and charcoal element:



A look inside the box where you can see the slot that the filter element material slides down into. Bunch of holes lets air flow towards the fan while keeping the element in place. The element is just hand cut from a larger piece (so just pennies per 'element'). You can see the tiny board that has the PWM controller. It runs from a 12V DC wall wart.



In the first picture you can see a small switch hanging on a thin cable (in front of the Rigol DSA), that is the control switch that turns the fan unit on (sleeps while off) and also varies the speed. It remembers the last used speed. Click to turn on, click to go faster (until it wraps back to the slowest speed), press to turn off.

Anyhow, all works very nicely and figured it may give folk some ideas.

cheers,
george.

[lincoln]

That's a nice build!

Dose anyone have any data on how effective those filters pads are at removing fumes / ash / VOCs?  I have the sneaking suspicion that any air filter you can see through isn't going to do shit at far as actually filtering the bad stuff and your just as well of as having a fan. ie "Dilution is the solution to pollution.."

[rdl]

That's a nice build!

I have the sneaking suspicion that any air filter you can see through isn't going to do shit at far as actually filtering the bad stuff and your just as well of as having a fan.

Where is the see through filter here? I only see one that looks pretty dense and black, though I doubt that has a lot to do with how well it filters.

[SeanB]

It will remove particles over a certain size, probably all stuff over 10 microns for a good one, or 500 microns for a junky one.

[lincoln]

> looks pretty dense and black

That's because your looking at it end on , previous employer had these on the benches. Even a new replacement element look like an open cell foam. The brisket fan they used wouldn't be able to pull air through a "real" filter like used in clean rooms or hell even an auto intake. Is there any data that show a 6 mm carbon filters pad in the cheap fume hoods do any good? Is just having a fan just as effective?

That's a nice build!

I have the sneaking suspicion that any air filter you can see through isn't going to do shit at far as actually filtering the bad stuff and your just as well of as having a fan.

Where is the see through filter here? I only see one that looks pretty dense and black, though I doubt that has a lot to do with how well it filters.

[smjcuk]

Nice job.

I built something similar back in the early 00s. It had two 80mm PC case fans (1 was probably enough!) and an industrial chemical mask filter sandwiched between with a fan guard on the front and back all on M3 threaded rods. The fans would stall if you used PWM so they went full revs while soldering whacked in my PSU.

I spent a fair amount of time avoiding things that bounced off the fan blades and extracting things that got sucked off the table. Plus you had to wear headphones because it was stupidly noisy.

I plan to revisit the idea in the near future with a little more sense. Thanks for the inspiration