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Old Jun 22, 2005, 11:40 PM
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DanL's Avatar
United States, MN, Brainerd
Joined Oct 2004
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Low amp smoke generator

I've built and tested a low amp glycol "smoke" unit that works pretty well. Wrote a construction article for our club including pics and would like to post it here. Its a long article , but I'll give it a shot. Will reduce the pic size for posting. The parts list is based on parts available at a local surplus store, but I'll include it anyway. Here goes...
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Last edited by DanL; Jun 22, 2005 at 11:48 PM. Reason: add pics
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Old Jun 22, 2005, 11:50 PM
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Additional pics

more pics:
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Old Jun 23, 2005, 12:50 AM
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PDX, OR
Joined Dec 2002
10,481 Posts
Very nice Dan.
Thank you so much for all the reseach, and materials condensed into a single article.

Now, what project to try this on...
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Old Jun 23, 2005, 05:09 AM
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Guelph, ON
Joined Sep 2004
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DanL,

Your timing couldn't have been better. Thanks for the article and excellent pics!
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Old Jun 23, 2005, 09:39 AM
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Motor City
Joined Dec 2004
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Great work!
On my smoker, I'm pulling 10A on 6v... looks like you've shown that a shorter bit of wire of appropriate gage can do the job at lower current. What I found was that the wire needed to glow dull red in free air to be hot enough to do the job. For a given voltage, there are all sorts of possible solutions- different combos of wire diameters and lengths can give the resistance needed to make a dull red glow. You can use tables and calculations, or just get a piece of wire and slide a pair of alligator leads along it till the color is right, measuring the current as you go.

Another hint- do a "failure test". While you are boiling off fluid, the unit will stay relatively cool. When it runs dry, heat will build up FAST inside the unit... I nearly burned down my tug this way. When you build your fog machine, do a test at full current with no fluid and the fan off, and check that nothing cracks or burns!

Pat M
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Old Jun 23, 2005, 09:43 AM
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Another hint- the crimped wire connection can work, but it also can work loose with thermal cycling, especially if you run the nichrome wire to red hot. Silver solder (the real stuff, not that 2% stuff sold at Radio Shack) will hold the joint at these high temps.
Pat M
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Old Jun 23, 2005, 10:14 AM
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smoker

Thanks much. Some additional info below...

Quote:
Originally Posted by patmat2350
Great work!
On my smoker, I'm pulling 10A on 6v... looks like you've shown that a shorter bit of wire of appropriate gage can do the job at lower current. Actually, your work was the basis for this design. The airflow you stressed is the real trick. The other key here is the use of a "percolator" effect to pump and evaporate the fluid inside a tight insulated tube for efficient energy use. What I found was that the wire needed to glow dull red in free air to be hot enough to do the job. On this unit, you can look at the inner capillary to see if the coil is hot enough to boil and percolate the fluid up thru the tube. If too hot, it sputters out the top as hot liquid . If just right, yoe see bubbles boiling at the bottom of the tube and wispy fog comes out the top of the tube. For a given voltage, there are all sorts of possible solutions- different combos of wire diameters and lengths can give the resistance needed to make a dull red glow. You can use tables and calculations, or just get a piece of wire and slide a pair of alligator leads along it till the color is right, measuring the current as you go. Exactly right

Another hint- do a "failure test". While you are boiling off fluid, the unit will stay relatively cool. When it runs dry, heat will build up FAST inside the unit... I nearly burned down my tug this way. When you build your fog machine, do a test at full current with no fluid and the fan off, and check that nothing cracks or burns! Right - od the test. The glass parts to use are high temp "chemistry lab" glassware. This unit is somewhat "triple insulated". When dry, the hot coil is fully enclosed in a glass capillary tube, which is enclosed by the glass preheat tube, which is enclosed by the glass reservoir tube/jar. Still not preferred to run dry, but at least some protection. Also, unit only runs at about 12 watts (12V x 1A) vs 60W (6V x 10A), so max T possible is probably lower.
Pat M
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Old Jun 23, 2005, 09:15 PM
Mostly harmless
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Sydney, Australia
Joined Feb 2005
382 Posts
Hey Dan,

Do you get any condesation onnthe inside of the stack. Do you have to allow for fluid dripping or do you just align it so it goes back into the resevoir?

Is there any cleaning required for this unit and roughly what is the life of the Nichrome element?

Cheers
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Old Jun 23, 2005, 09:36 PM
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Catain -
there is some condensation inside the metal tube that I call the stack liner. The tube sits aligned directly over the preheat tube and is slightly larger in diameter than that tube. The reservoir tube is larger in diameter than the stack liner, so all drips go back into the reservoir. I've run maybe a total of 40 hrs of smoke, usually in 1 to 2-1/2 hr sessions, and there have been no sloppy messes.
After each run, I pop off the outer styrene stack, the aluminum tube liner stack, pull out the heater assembly, spray all with household ammonia cleaner, rinse with hot water, shake off and set aside to dry. Takes 2 minutes.
The weak point of the heater wire is not burnout - you just don't run it that hot. The failure point is the connections to the power wires. I've had one broken connection. After fixing it, I covered the whole connection area on both power leads with Permatex hi temp RTV (see the pic). It has stabilized the connections, not allowing "jiggle" that leads to broken wire.
Note that the alignment is important to get the vapor from the top of the percolator tube into the throat of the stack, and to get the best effect of the air nozzle that generates an upward airflow thru the stack as the injected air escapes.
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Old Jun 23, 2005, 10:09 PM
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Captain C - some pics

Here are some pics of the actual stack on the tug Rosco
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Old Jun 26, 2005, 02:25 PM
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Motor City
Joined Dec 2004
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Anyone building a smoker? I have a pair of minature 12v computer fans, cost me $12 each, that I'm not going to use. 1.3 cfm, which is the same capacity I used on my tug, blows CLOUDS of fog out. These are square case fans, fully enclosed, but what's neat is they're only 1 inch square! Tiny and quiet.
$6 each, and I'll cover the postage in the US.

Pat M
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Old Jul 14, 2005, 08:45 PM
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Scottsdale, AZ
Joined Jul 2005
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I' ve built a smoker from Dans instructions with a few mods, and hooked the fan directly to the motor on my tug so the smoke increases with motor speed. Works fine fwd. but in rev. the cabin fills with smoke. Does anyboby know of a way to get this to work in rev. The main motor is controled by an esc.
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Old Jul 14, 2005, 09:04 PM
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Motor City
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A diode bridge will "rectify" the current to fan. Sketch to follow.
Pat M
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Last edited by patmat2350; Jul 14, 2005 at 09:21 PM.
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Old Jul 15, 2005, 12:29 AM
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Scottsdale, AZ
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Thanks Pat & Dan for all there info. Will work on it and see how it goes.
Jim
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Old Jul 16, 2005, 03:39 PM
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North-East England
Joined Mar 2002
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Umi - you ask which project? - Answer is 'any project - you won't be able to see it for the smoke!

Nice one Dan.

Tony
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