Need help selecting a power supply for a grid-style hotwire foam cutter

Discussion in 'Power Electronics' started by Hotwirefoam, Jul 12, 2016.

  1. Hotwirefoam

    Thread Starter New Member

    Jul 12, 2016
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    Greetings,

    I am building a hotwire cutter that uses a grid of wires instead of a single wire to cut foam. The grid is approximately 12" wide and 48" long and will be constructed of 18g or 19g stainless steel wire. The grid will be divided into 1" squares. I know that a single wire foam cutter can be powered by a 12v power supply, but I am having trouble calculating the amount of power I will need to heat this grid to a temperature suitable for melting polystyrene. Any help will be greatly appreciated. Thanks!
     
  2. EM Fields

    Member

    Jun 8, 2016
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    http://hotwirefoamcutterinfo.com/_NiChromeData.html
     
  3. BR-549

    Well-Known Member

    Sep 22, 2013
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    +1 on that one. Great question. How does current flow thru chicken wire. This is gonna be good.
    Do you have a schematic for the present system?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have built a single wire foam cutter but in your case I would look at having the X & Y axis operate separate and independently operate one axis then the other, this way all the elements will be in parallel at any one time.
    Max.
     
  5. Hotwirefoam

    Thread Starter New Member

    Jul 12, 2016
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    I thought about operating the x and y axis separately, but for my particular application having the whole grid heat up at once will be a huge time saver. After reading the link EM Fields posted, I am still unsure of how to calculate the requirements for the power supply I will need. The link provided was specifically for nichrome wire. I will be using stainless steel 18g, 19, or 20g at the absolute thinnest. If I assume that stainless steel is comparable to nichrome when it comes to resistance, will I be calculating my psu requirements on the total linear inches of the grid? If so, I am looking at a very large number of linear inches. If my calculation for linear inches is correct, I will need to raise the temperature of 1,261 linear inches of stainless wire to a degree that will melt foam. I don't think I will need it to be 600 Fahrenheit. I just need to make it hot enough to melt the pattern of the grid onto the top surface of the foam.

    And thanks for the fast replies.
     
  6. BR-549

    Well-Known Member

    Sep 22, 2013
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    I would use separate nichr wires for both axis. I would separate the axis, a little more than the stretch of the wire.
    Increase vertical stroke a little to make up for it, if needed.
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    If you look up the solution to this nerd sniping puzzle, it may shed some light on that question:

    upload_2016-7-12_12-58-26.png

    Source: https://xkcd.com/356/

    I believe it is a fairly standard problem and well-known solution. The fact that your grid is not quite infinite doesn't mean the principle won't apply.

    John
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You could either do it by creating the grid and measure the resistance, it won't get that hot to melt foam so the cold resistance will be close, or you could set up a supply and carry out an empirical test using an automotive battery etc.
    Max.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    More seriously and based on my somewhat limited experience wire-cutting foam, I would not use a grid. That is, the horizontal and vertical wires would not be in the same plane.

    In one plane, I would have the horizontal wires -- probably wired in parallel with an independent current control for each wire, if necessary. A small value balancing trimming resistor in series with each wire might work. In a second plane, I would have the vertical wires. I would separate the planes by more than the sag of the horizontal wires -- as a start, maybe 2 to 3 X the sag or 2", whichever is greater.

    John
     
    Last edited: Jul 12, 2016
  10. MaxHeadRoom

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    More or less as in post #4.;)
    Max.
     
  11. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The original question is lacking some details, but IF the goal is to have a single voltage source with only two connections to the wire grid (+ and -, in and out, whatever), this will not work. There is nowhere you can connect the source of current that will assure equal current in all wire segments.

    ak
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    It may have been EPE magazine that published a switchmode driver for this purpose a year or so ago.

    It was a variable regulator AFAICR.
     
  13. BR-549

    Well-Known Member

    Sep 22, 2013
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    post #6 has one dc power supply, and is continuously heated. And one stroke operation.

    I thought the app was for cutting. Are there any other conditions? You just want to burn a surface design, is that right?
     
  14. BR-549

    Well-Known Member

    Sep 22, 2013
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    The x axis doesn't touch the y axis.
     
  15. Hotwirefoam

    Thread Starter New Member

    Jul 12, 2016
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    Indeed this project is more for burning the design into foam rather than cutting it. I would prefer to use a large power supply wired in series. The material I will be using will be stainless steel chicken wire if possible.
     
  16. Hotwirefoam

    Thread Starter New Member

    Jul 12, 2016
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    If I did wire a power supply in series to this 12" X 48" wire grid, what ballpark am I looking at as far as power supply units go? I don't think using a power supply for each leg of this 12" X 48" grid will be feasible.
     
  17. EM Fields

    Member

    Jun 8, 2016
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    The x axis doesn't touch the y axis.[/QUOTE]

    I don't think that's true.
    How would you solve the OP's problem from your point of view?
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would be inclined to make up a simpler smaller scale version to see if it is viable to get even conduction heating from a grid that will give you satisfactory results, if this is the method you want to pursue,
    Max.
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I suggested powering each axis separately but the OP wants expediency and also apparently it is not foam cutting as in all the way through, but just top marked.
    Max.
     
  20. BR-549

    Well-Known Member

    Sep 22, 2013
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    EM Fields, I was referring to my solution, but I thought he was cutting, not burning a design on surface.

    Edit: "I am building a hotwire cutter that uses a grid of wires instead of a single wire to cut foam."
     
    Last edited: Jul 12, 2016
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