DIY Benchtop Fume Extractor

[linuxgeek]

I know this is not exactly Teensy related, but I hope you can indulge me since this is just a basic tool that others might be interested in.

My son is joining Hacker Scouts, which will entail lots of kids soldering together in a room. I had some concern about the fumes for the kids, and was thinking that a DIY Fume Extractor could be a project that the kids could assemble.

I was thinking a 120mm computer fan with a carbon filter & hepa filter should do the trick. It seems to me, most fumes are breathed in cause they rise up directly to the person soldering. So this benchtop would just suck it out horizontally outward, and likely capture most of it in the filters. I guess making them easily replaceable would be a plus.

I found this instructable, which doesn't seem bad.
http://www.instructables.com/id/DIY-Fume-Extractor/

But I was thinking that a DC-12V 120mm computer fan might be better for more CFM, but I'm not sure the easiest method for supplying the power from 120V AC.
Any ideas, either for good/inexpensive fan, PS, or case?

Since this would be their first project, I'm thinking the adults can machine the case if need be, but everything else could be assembled by the kids.

Down the road, I think adapting a computer Power Supply would be a good thing for providing bench power to various projects, but that's a little more complicated and requires more caution.
http://www.instructables.com/id/ATX-->-Lab-Bench-Power-Supply-Conversion/

Thanks.

 

[PaulStoffregen]

But I was thinking that a DC-12V 120mm computer fan might be better for more CFM, but I'm not sure the easiest method for supplying the power from 120V AC.
Any ideas, either for good/inexpensive fan, PS, or case?

The safest power supply would be a "wall wart" power adaptor. 12 volts DC is a pretty common rating, so maybe you can find some used or cheap? If not, you can always buy they online.

Down the road, I think adapting a computer Power Supply would be a good thing for providing bench power to various projects, but that's a little more complicated and requires more caution.
http://www.instructables.com/id/ATX-->-Lab-Bench-Power-Supply-Conversion/

There are a couple of gotchas when using PC power supplies.

The worst issue is many modern ones don't work well until they're delivering at least 1/2 an amp, sometimes even a full amp, on their 12 volt lines. There's one old thread were someone blew a Teensy3 with one of these supplies, which turned out to be driving over 7 volts with lots of noise onto its 5V line when there was no load on the 12V part.

Even if you get a power supply that's well behaved voltage-wise, they make pretty terrible lab bench power supplies for experimenting with electronics. The one really valuable feature you need in a bench power supply is the current limit. Ideally you would set it to some current that's not much more than your project should need. For a Teensy3-based project with 5 LEDs, you might try 100 mA, since Teensy3 uses about 27 mA and the LEDs might use 10 mA each.

The current limit saves you from mistakes by reducing the voltage if you hit the current limit, so the current won't go any higher. It's still pretty tough on parts, but usually when you connect a transistor or LED or something else incorrectly, and especially when you accidentally short the power, the current limit keeps the current at a reasonably low limit so your odds of damaging stuff are really low.

PC power supplies can output pretty incredible amounts of current. Some can reach almost 100 amps. That's great if you're a gamer with several power hogging graphics cards. But for experimenting with electronics, it's just about the worst thing you could want. That much current available to flow through any accidental path pretty much guarantees any mistake will be fatal of the parts involved.

 

[linuxgeek]

Great. That's what I was starting to conclude. I'd feel much better knowing the dangerous power levels are all contained within a wall wart, and not part of the unit the kids are assembling.

I'm thinking this for 12V power supply:
http://www.newegg.com/Product/Product.aspx?Item=9SIA27J0SG6362

And this for a 12V fan:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835220014

Activated Carbon filter here:
http://www.amazon.com/gp/product/B000U204W2#productDetails

And an aluminum case, something like this:
http://www.frys.com/product/1656594?site=sr:SEARCH:MAIN_RSLT_PG

I know this is a naive question, but what happens to the extra amperage from a wall wart? My understanding was that extra amperage is typically fine, but is that only true for devices that have active circuitry to only consume so much? Will the fan only consume a certain amperage? Do I need to be concerned about providing too many amps to the fan?

I like the idea of having the fan controller, but will this work outside of a computer case? I believe it's PWM control, but I'm not clear on the specific of what is generating the PWM.

And I realize I need activated carbon filter, not just a carbon filter.

The other thing I'm not sure is if it's better to have the fan push the air thru the filter or suck it thru the filter.

This site had some more info:
http://www.mobilewill.us/2012/08/diy-fume-extractor.html

...

And thanks for the info on the lab bench power. I'll forgo that.