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Old Nov 11, 2012, 05:05 PM
kad
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United States, NY, Poughkeepsie
Joined May 2012
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Soldering Fume Extractor

Problem: My mini-fume extractor (ala MAKE Magazine article) didn't have sufficient suction and ate batteries like Lays potato chips (Betch'ya can't eat just one!) and I wasn't willing to pay $50-$100 for a commercially produced unit.

Solution: Build a bigger/better one myself!

Supplies:
  • 2 x 2.5" 12v 1.2amp fans out of an old IBM server
  • 1 x 16v DC IBM Thinkpad power supply
  • 1 x Pelican 1150 case *
  • 2 x Toggle switch (Radio Shack) (I want to control each fan separately)
  • 1 x Panel mount DC jack. (Radio Shack)
  • 3 x LM7812 Voltage regulators
  • 1 x 1000uf Capacitor
  • 2 x 100uf Capacitor
  • 9 x 1 Ohm Resistors
  • 1 x Heat sink. (Small aluminum heat sink that had held 3 LM78xx's on something I disassembled)
  • Piece of perf board
  • Carbon filter medium

* Note: I would not normally have used such an expensive item for this project, but I got this one for free after buying it on eBay and receiving it with a cracked latch. The seller refunded my money, but did not want the case back. It also already had a 1" hole drilled in it with a waterproof connector for a battery system of some sort.

Tools:
  • Soldering Iron & Solder
  • Fordam Tool (Or Dremel) with cutoff wheel
  • Drill press w/ Circle cutter and assorted drill bits
  • Hot Melt glue gun
  • Assorted hand tools (clippers, screwdrivers, etc)

Problem: My fans are 1.2amp draw, but the LM7812s are only rated for 1 amp. As the 78xx series are not precision items, just hooking them in parallel will result in the lowest voltage one taking all the amperage, overheating and shutting down, then the next and so forth.

Solution: A quick hunt on the web turned up a circuit design for hooking LM78xx's up in parallel with a load balance system that only requires a couple of caps and a handful of resistors.

The only items I didn't have on hand were the switches, the dc jack and the perf board. One quick trip to Radio Shack (For those outside the US, Radio Shack is the closest thing to an electronics supply store in most of the US. 25 years ago when I worked for them, they were a real supply store. Nowadays... Not so much.)

A little measuring and then out to the shop:

I used a circle cutter in the drill press to cut out two 2 1/16" circles on the bottom of the case for the fan outlets. The fans have built in grates, so no protective grates will be needed. I then simply used one of the fans as a guide to drill the bolt holes for the fans.

I removed the old power connector and bolted on a small patch, then drilled a smaller hole for the DC jack through that.

I drilled the 2 x 3/4" holes for the switches with a hand drill and a 3/4" forstner bit, as the pelican case wouldn't sit flat and square on it's edge on the drill press table to do it.

I then cut out most of the flat are of the lid with the cut off disc in the Fordam, in an area I could fit one of the 6"x6" filters I had behind, leaving a bar across the middle for support.

I soldered up the voltage regulator unit, bolted everything into the case and cut out a piece of cardboard to brace the filter from behind and fired it up. It's louder than the little one, but it sucks the fumes from a much larger area much faster.


-K
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