# Fog on demand



## halfcracked (Oct 13, 2006)

OK I'm about to throw my american DJ fogger through a window.

I'm using it in a Stage production & it needs to produce fog on cue. How ever for the last 3 shows it's decided to be in a down cycle when the cue came up.


What I want to know is do the "continuous" foggers really never go through a cool down cycle? I'll get one if I can be guaranteed that when I press the button there will be fog even when the thing's been sitting idle for 20 min.


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## corey872 (Jan 10, 2010)

Interesting question - and one I'll eagerly await an answer to. I only use mine for the basic 'around the house' fogging, Halloween, parties, etc. But I've noticed it does the same thing - sometimes I want a little fog and it's 'off line'!

I can't think of any reason why it would need to be off. I mean it has already warmed up - if it is 'cooling down' it will just be warming up again, eventually. My furnace doesn't shut off in the middle of the night and cool the house to 32 only to warm it back up - at least that I know of!

Hopefully someone out there has already cracked the case, if not, it may be time for some exploratory surgery!


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## niblique71 (Dec 2, 2009)

I have the same problem every year. My solution wasn't elegant. I just bought more fog machines. It's not a perfect solution by any means. I stll ran out of fog at critical moments on occasion, but it did greatly improve the odds of having fog on demand. You need a 100% reliable solution, and I'm eager to hear what others have done.


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## Otaku (Dec 3, 2004)

Most fogger heaters use a simple bimetallic thermostat to tell them when to come on. Higher end machines use a thermocouple and microcontroller combination to control the heating profile. The point is, most machines simply heat up and immediately start cooling off. When they get cold enough, the heaters come on again, usually at a much lower wattage than the initial startup power. This helps prevent temp overshoots and burnouts.

Without some kind of PID (proportional-integral-derivative) control there's not a lot that you can do. A PID control system allows you to adjust how much power the heaters get, control the power ramping and prevent temp under and overshoots. Even a fairly low end controller like a Watlow 93 series:
http://www.instrumart.com/Product.aspx?ProductID=20977&gclid=CNKZktKXyqACFRdSagodsXKkZg
can cost $$$, which is why the low-end foggers use a brute-force approach to controlling the heaters.
There's been a lot of discussion about how to get fog-on-demand. Some of it centered around being able to know exactly when the fogger is ready to go. I remember some circuit designs and concepts were posted here and on Halloween Forum.
The bottom line is that without a continuous-mode fogger you're still rolling the dice.


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## randyaz (May 26, 2006)

If you really want to learn about Process Control and PID an excellent resource is this Parallax "Stamps in Class" tutorial

http://www.parallax.com/Portals/0/Downloads/docs/prod/sic/Web-PC-v1.0.pdf

PID can be accomplished fairly inexpensively with a basic stamp2 or EFX Prop2/SX. Chapter 8 of the text deals with maintaining an incubator temp and could be adapted to the fog heater.


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## corey872 (Jan 10, 2010)

Otaku said:


> Most fogger heaters use a simple bimetallic thermostat to tell them when to come on. ...


That is pretty much what I've come to conclude dissecting my machine today, too. The PID option is tempting, although adding a bit of complexity. PID controllers can be had for ~10% the cost of that Watlow unit - but still, a $30 controller for a $30 fogger?!?

I wonder if one option might be to smarten up the people and leave the machine dumb? My first thought is even a fogger which has warmed up, but is 'cooling' or 're warming' is probably still hot enough to make fog. So a person could bypass the 'heater-or-pump' circuit and wire it so the pump always runs when you push the button. You'd just have to be smart enough to know to let it warm up first, and that you can only press the button for a set time / number of times before letting the machine warm back up.

Of course the down side is you risk loading up the heat exchanger with juice and having it erupt as the barrel warms up, or worse yet, squirting a stream of hot juice out with no real fog.

I guess the other option would be to time the machine and see if it reacts the same each time. Say you turn it on at T=0, at T=5 it's ready to go, but T=15 it's gone offline to heat again, then T=18 ready again. So ideally you'd want to turn it on ~ 7 minutes before it's really needed to catch it in the 'good' phase.


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## Mr_Chicken (Nov 26, 2008)

I used two fog machines in a theatrical production back in December. We figured out how long it needed to warm up (5-10 minutes) and just had a stage hand power it on that far away from the cue when it would need to be fogging. We unplugged it after that cue and repeated the procedure for subsequent cues.

The problem is that the machine gets too hot and turns itself off to cool down. By cutting the power when it's not needed, you prevent this from being an issue...provided you can get it plugged back in with enough time for it to heat up again.

Now, we still had a problem with the quantity of fog the machine could put out on that cue, but that's another story :xbones:


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## randyaz (May 26, 2006)

just for the conversations sake...

I have seen homemade foggers using an old iron and a drip. the iron stays at pretty much a constant temp.


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## Otaku (Dec 3, 2004)

randyaz said:


> just for the conversations sake...
> 
> I have seen homemade foggers using an old iron and a drip. the iron stays at pretty much a constant temp.


Hey, I always wondered if that design actually worked. Do you get much fog out of one of those, and how fast can you run the drip?


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## billman (May 3, 2006)

Was watching the pacific on hbo and the water cooled machine guns gave me an idea.
What about adding a cpu water cooling unit? That might keep the temp down enough to operate on demand.


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## fritz42_male (May 5, 2009)

On a side issue, has anyone seen a small fogger unit suitable for a hand-puppet size prop? Homemade or commercial. I bought a Wizard stick but it was disappointing and not easy to engineer to what I want.

All the smaller foggers seem to have disappeared from the market.


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## randyaz (May 26, 2006)

well...I didnt personaly witness one. There used to be a couple of websites that documented it, but, they no longer exist. The things put out a good amount of fog. They basically built a box and mounted an inverted iron under a tank with a hose restricted to provide a slow continuous drip.

There is a video of rinky dink one but the ones that Im talking about put out far more fog. 
http://hackaday.com/2009/10/15/halloween-prop-diy-fog-machine/


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## Otaku (Dec 3, 2004)

fritz42_male said:


> On a side issue, has anyone seen a small fogger unit suitable for a hand-puppet size prop?


There was a very small unit available last year - someone posted a link on one of the forums. Looked pretty good, but the price was ~1K.

Found the link:

http://www.theatrefx.com/moreinfo_fg90_tiny_fogger_fog_machine.html


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## fritz42_male (May 5, 2009)

Nearly 2K for a mini fogger! 

I think it will either have to be DIY (got an idea based around a Butane hot knife) or an aerosol smoke can with servo triggering.


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## halfcracked (Oct 13, 2006)

Mr_Chicken said:


> I used two fog machines in a theatrical production back in December. We figured out how long it needed to warm up (5-10 minutes) and just had a stage hand power it on that far away from the cue when it would need to be fogging. We unplugged it after that cue and repeated the procedure for subsequent cues.
> 
> The problem is that the machine gets too hot and turns itself off to cool down. By cutting the power when it's not needed, you prevent this from being an issue...provided you can get it plugged back in with enough time for it to heat up again.
> 
> Now, we still had a problem with the quantity of fog the machine could put out on that cue, but that's another story :xbones:


Yeah, I've done this before but it's a ROYAL PITA.
Especially if you have more than one cue for a show.

I guess what I really want to know is if i shell out for one of the higher end "Continuous" foggers do they have the same issues?

I'm looking at this fogger

but I won't spend the money if i can't be sure of getting fog when I need it.


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## halfcracked (Oct 13, 2006)

hrmm VEI seems to be a popular maker
the V960 El Capitan DMX Fogger looks like a nice package.

Any one have one of these & can tell me if it's ever shot blanks on them?


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## RandalB (Jun 8, 2009)

Haven't played with it a whole bunch, but from what I've seen, the v960 doesn't have a cool down cycle. You hit continuous fog or the remote and it will run until it runs out of juice. 

You can hear the pump cycling but it hasn't gone into a warm-up cycle other than the initial powerup that I've seen...

HTH,
RandalB


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## ouizul1 (May 22, 2010)

As for small puppet sized foggers, I did pick up a small handheld one at Toys-R-Us last year. It's pistol shaped and was originally designed as a fog filled bubble blower. The heater is powered by AA batteries, and the fan and juice pump were powered by a squeeze handle...kind of like a label maker trigger. The pump was actually just a plastic tube with a one way valve. If you can find one, it can easily be torn down and the guts relocated to a puppet. The fluid tank only held like an ounce of juice though.


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## scream1973 (Dec 23, 2007)

Half Cracked we installed a similar unit for a commercial dance bar at one point and it basically produced fog for around 30 minutes straight before it ran its 5 litre tank dry. So i think the long and the short of it is a continous duty fogger will meet the requirements you have following the initial warm up period.


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## DrUnK3n_PaNdA (Sep 17, 2009)

Well to the best of my knowledge, at least it's true of my fog machine that it takes a rather consistent time to heat up. You said you're using it for a stage show of some sort... Would it be possible to just time the amount of time it takes to warm up and have someone off-stage plug it in that long before the cue? 

May seem a bit insultingly simple... but if your's heats at a predictable rate, then it would get the job done.


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## halfcracked (Oct 13, 2006)

The problem isn't so much the fogger being predictable as the performers.
My experience has been that the que will vary it's timing depending on how well the show is going. lines dropped, Shatnerian moments, audience interaction, etc.

Ive seen a que vary by as much as 10 min. relative to the start of the show so it's hard to tell when you're going to be X min. away from needing the fog & if the fogger only stays hot for 5 min or so you can miss the cue that way too.


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## psyko99 (Jan 11, 2008)

My cousin is a tech director for several small regional theaters and is a theater prof at one of our area colleges. He still uses the old standby of a barrel of water and dry ice. The lid has a squirrel cage fan and a dryer hose leading to the stage. A stage hand drops in the dry ice on cue.


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## scubaspook (Dec 16, 2010)

I know that this thread is probably moot by now but here is what I found. I couple years ago kmart had a constant fogger in the 30 dollar price range. Guess what? It actually worked. Once it warmed up no matter when you pressed the button it put out fog. After a couple of years the pump quit working (my faukt probably as I never worried about cleaning the unit after use and it rusted out the spring mechanism in the pump). HoweverI did notice that this fogger had 2 temp dics on it instead of 1 that the rest of y cheap units have. Maybe that is the key is having 2 temp units.


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## Otaku (Dec 3, 2004)

IIRC, that was the "secret" behind the old Lite F/X constant foggers - two 400W heaters and nozzles instead of a high watt heater and microprocessor control. Unfortunately, they didn't last too long in many cases.


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