I want to build a fume extractor and was wondering what fan i should use. I've made one before with a pc fan but it doesn't work well when the pcb is farther than 10cm from the fan.

Should i buy a fan that has the biggest m^3/h rating, wattage or rpm? Which one is more important?

thanks

 

For fans, the most important rating is m^3/h rating and pressure gradient (as with any air pump). Your pressure gradient will be very low (inches of water).

Perhaps your problem is the enclosure or lack thereof? On an open bench, the airflow needed will be a lot greater then in some sort of enclosure. For example, consider a vacuum cleaner. How effective is the wand if more than a few centimeters form the surface? There are several designs for fume/safety hoods.

 

This is my existing extractor:

So what you are saying is that there should be an enclosure before the fan just like the vacuum cleaner? Interesting.
Also, i will try to get the fan with the biggest m^3/h rating.

 

If you want to visualize airflow, you can use a match flame, cigarette smoke, or similar. One problem with your design is that the drawing area is larger than needed. Fume extractors (as opposed to whole fume hoods) are usually designed like this:



You can visualize airflow across the surface but not much a few cm above it. Side baffles may help. A smoke test will help visualize it. A 3" x 12" rectangular duct (face area 36 in^2) connected to your current duct tubing will be more effective than your current square box, which looks to be about the same open face area.

 

The ones we used on a recent job assignment consisted of a flexible hose about 1 1/2 inch diameter. The hose was connected to the ring lamp. If you were using a microscope the hose was mounted just out of sight of the scope. Fumes would naturally rise with the heat and then find their way into the extractor. The fan unit itself was a larger unit because there were four benches connected to one extractor. And it didn't vent outside, it passed the fumes across a carbon filter.

At home I simply have a small computer fan by the work. It draws a gentle airflow taking the smoke away from my face. I've always noticed that no matter where I sat or stood - without extraction the smoke ALWAYS found my face. But at home the fumes are dissipated in the room. I don't do a ton of soldering, so having the fumes drawn away is sufficient. No need for filtration or ejection out-doors.

Come to think of it - there's a fume extractor adjacent the kitty litter box. The wife complained about her clothing smelling like the litter box (in the basement where she did laundry and would hang her dresses instead of the closet). This extractor is actually an old vent fan from a stove that vented smoke down (instead of over the stove) and ejected the fumes outside. I have an old ceiling fan remote control box that allows a ceiling fan to run on low, medium or high. The light bulb control portion went bad, so it's largely useless. Except in that it now runs the fan on ultra low speed giving the gentlest draw just above the cat box at all times. When scooping the litter I switch the fan to high so that any dust or odor that may be released is drawn outdoors. It shares the dryer vent where it exits the house. I installed a back flow preventer so that when the gas dryer is running fumes from the dryer are blocked from coming back into the house. And for anyone who may worry about this practice, there's a carbon monoxide detector nearly directly above the water heater and three feet off from the dryer. The furnace is adjacent the water heater too. So any carbon monoxide will be quickly detected and ring all three alarms.

There's an alarm in the laundry room (CO and smoke), an alarm in the family room (fireplace) and the one in the upstairs hallway where all three bedrooms are located. That's the one that is most often set off when the wife is cooking. She's been asking me to invent a smoke detector that can be silenced simply by yelling "I'M COOKING!" So far trials are not going so well.

 

That's the one that is most often set off when the wife is cooking. She's been asking me to invent a smoke detector that can be silenced simply by yelling "I'M COOKING!" So far trials are not going so well.

Yell back at her, "QUIT BURNING THE FOOD!"

 

That's the one that is most often set off when the wife is cooking. She's been asking me to invent a smoke detector that can be silenced simply by yelling "I'M COOKING!"

How far down from the ceiling is the detector? Does your wife use the hood over the stove when she's cooking?

 

That's the one that is most often set off when the wife is cooking.

That's how we knew that dinner was ready at my house.

 

We had a detector I used to refer to as the "Toaster Alarm" and you didn't have to burn the toast to set it off. It is a lot easier to blow fumes away than to suck them in. Most DIY use a 12VDC muffin fan from an old computer and a layer or two of activated charcoal filtering screwed or glued on. I haven't found the need for one and quite like the smell of rosin core flux. I also worked my way through college for a couple of years stick welding with all of its resultant smoke/fumes with no ill effect and there were many welders who had been doing it for decades with no health effects. Smoke isn't always bad for you and the amount of lead particulate in solder fumes is not significant for the usual person in electronics who doesn't solder 8+ hours a day as a career.

 

Are you wanting to remove the smoke from the room entirely, or just get it away from your face? If you just want to get it away from you, there are various versions of this around. They don't work that well if you're more than a couple of inches from it though:

https://www.amazon.com/gp/product/B00RLEB6AG/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Being from that part of Florida, I feel it only appropriate to suggest a more user friendly smoke detector for those who often burn the food: