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In the midst of building Fog Machine...have questions

Discussion in 'Special Effects' started by Thefoxygranpa, Mar 14, 2009.

  1. Thefoxygranpa

    Thefoxygranpa Active Member

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    ello CB!

    For my senior project in highschool I'm creating a Dry Ice Fog machine...but would appreciate some help on a certain part.

    What would be a good Water/Dry Ice ratio to have good, thick fog run continuously for 5 minutes? I have worked with the Peasouper in the past and that machine was wonderful, but I forgot to measure how much water I used.

    If possible I would like to use 15 lb of dry ice, and have it run for a minimum of 5 minutes.

    Thanks for the help all, and I'll be sure to post some pictures of it in the works!

    Cheers
     
  2. icewolf08

    icewolf08 CBMod CB Mods

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    There is no formula for this, dry ice is an art, not a science. The only way to figure it out is to test. There are so many factors that affect how the fog will look (ambient temperature, relative humidity, water temperature HVAC status, number of audience members, etc.), and it varies from day to day. Then consider that the size of the chunks of dry ice that you use will make a big difference. Smaller chunks will give you a lot of fog fast but won't last as long. On the other hand, if your chunks are too big they will ice over (with H2O) and not produce any fog. Also, the speed at which you lower the ice into the water will have a big effect on how much fog and how long it lasts. So, you have to play with it to figure out chunk size, how much ice you need, and drop rate to make it work effectively.
     
  3. Thefoxygranpa

    Thefoxygranpa Active Member

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    Thats the answer I thought I would get :) . Right now I have a 15 Gallon tank I am using for the water, I'll start with 8 gallons and see where that gets me, if anybody thinks I'm shooting too low on water content let me know!

    And thanks for the quick reply!
     
  4. icewolf08

    icewolf08 CBMod CB Mods

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    In general, with the volume of ice that you are talking about you need way more water and really good heaters. This is why most people make these machines out of 55 gallon drums. Even with a really good heater you probably won't be able to keep 8 gallons of water hot enough to pump out fog for 5 minutes.
     
  5. jwl868

    jwl868 Active Member

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  6. Thefoxygranpa

    Thefoxygranpa Active Member

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    Thanks...I'm trying now to raise the amount of water 10 gal and reduce the amount of dry ice, also figuring out my basket system so maybe if i drop it in increments, it can keep the amount of fog continuous.

    My main concern isn't so much for length now really, though to have over 2-ish minutes of nice fog wouldn't be bad :) .

    I'm graded on how my research was applied to my product really. Thanks for all of your help, and if anyone else has some input that would be greatly appreciated!

    Cheers
     
  7. kiwitechgirl

    kiwitechgirl Well-Known Member

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    You should be able to get 5 minutes of fog out of a decent machine - I did a production of Grease where we had dry ice covering the stage for the entirety of the Beauty School Dropout scene, which is close on five minutes long, and the Suicide in Les Mis is about that length as well. We used to drop about 15kg of dry ice pellets for each of those cues, and would normally have some left over at the end of the scene. I have no idea how much water we used though - it was a big tank! What we found to be more critical was temperature. For both of those drops, we found that running at 65-70 degrees Celsius worked really well - but that we found through trial and error. It's a very inexact science!
     
  8. Thefoxygranpa

    Thefoxygranpa Active Member

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    Did a test last night to see how hot i can get the 10gal of water....i had it up to 175 and it was still climbing with the "Bucket Heater" used in a previous post about someone creating their fog machine. Thanks for your input!
     
  9. BillESC

    BillESC Well-Known Member Premium Member

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    Having built several thousand dry ice fog machines back in the 70's I think you should consider a different approach.

    Install two 1500w domestic hot water heaters as close to the bottom as possible. Install a fixed basket about 6" from the top of your drum. Using a sump pump, you'll draw the water from the bottom of the drum and expel it onto the dry ice.

    You'll need to experiment as to what CFM sump will give you the desired duration.

    We built custom machines for Xenon and Studio 54 in NYC using domestic hot water pumps installed onto 55 gallon drums that would hold 150# of dry ice and it worked very well.

    Sometimes it's easier to lead the water to the horse than the horse to the water.
     
    Last edited: Mar 15, 2009
  10. Thefoxygranpa

    Thefoxygranpa Active Member

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    Hmm I never thought of that approach. Sadly I present this fog machine tomorrow, I wish I spent a little more time on it.

    I'm looking to build another one in the near future, I think I'll be going this route when doing so.

    Cheers
     
  11. Van

    Van CBMod CB Mods Premium Member

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    This approach is similar the set-up I've always had luck with.
    I use 2 1500 watt elements, an interior basket, I usually mount a squirrel cage fan scrounged from an old overhead range hood, if I'm being cheap, or one of these if I'm being luxourious. I install a pipe on the outside of a 55 gallon drum with flanges and intall one of these type of circulating pumps in line. Run the pipe up and back through the top. Install a cheap showerhead and adjust the flow so it showers the ice basket evenly.

    I'll see about posting some pictures ar drawings of one I have built.

    The really important thing to remember here is that you are using water, extreme heat, extreme cold and electricity all in the same little machine. All electrical work should be performed by a qualified individual, and inspected by a qualified electrician. GFCI should be used when supplying power to a device such as a Dry ice/water fog machine.
     
  12. cdub260

    cdub260 CBMod CB Mods

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    Here's a relatively inexpensive GFCI adapter.

    A simple Google Search will find various GFCI adapters ranging from $13.00 to $75.00.
     
  13. Thefoxygranpa

    Thefoxygranpa Active Member

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    Well I presented my machine today for a grade and it passed. And I did use a GFCI, same one that was in the previous post.

    It worked a lot better than I thought it would, and lasted a good three minutes before dying down in intensity.

    I'll be sure to post some pictures of the final product once I find my camera...
     

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