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Need Help With Element Cals For Oven Build

Discussion in 'Forges, Ovens, Kilns, & Salt Pots' started by Bluefish, May 6, 2018.

  1. Bluefish

    Bluefish New Member

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    so i'm in the works of building a Heat treat oven and looking to get supplies to make coils, trying to run the numbers for coils and am really failing at understanding how it all works together. i'm pretty handy with everything but electrical so need some guidance. i can get 20 gauge wire in 50 foot length so i will be running with that.
    So this is what i know or have, will be running 120volts on a 20 amp breaker.
    Inside oven dimensions will be 4.5" x 4.5" x 15"
    2 x 50 foot rolls of 20 gauge wire
    Not majorly concerned about heating up super fast, i can run 1/2/3 coils.
    Have PID and 40amp SSR on the way

    I've looked at dcknives spread sheet and tried to make sense of the numbers to work with my application but i just don't understand what it's telling me. below is a copy paste of what i got.

    INPUT VOLTAGE 120 V
    DESIRED WATTAGE 3000 W
    NUMBER OF ELEMENTS 2 QTY 1 or 2 elements only
    AMPERES (DO NOT EDIT) 25 A
    OHMS (DO NOT EDIT) 9.6 Ohms
    COIL DIAMETER 0.375 inches

    Length of wire 20 AWG 11.75
    length per coil turn 0.98 in
    Turns per inch 31.25 turns
    Turns per foot 375.00
    Wire per foot of element 30.53 ft
    Coil length 0.385 ft 4.62 inches
    Stretched coil length 0.770 ft 9.24 inches

    If i'm reading this right i need 11.75 Ft per coil which i will be running x 2, i will turn them around a 3/8" shaft, i need 31.25 turns per inch for 4.62 inchs = 144.375 turns total each element.
    each element will be 9.24 inch when stretched out.

    The above is all fine and well but when i compare to a other gauge wire in the same spread sheet it seems pretty short, What am i missing here?
     
  2. dancom

    dancom Dust Maker Best Shop Tool

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    Try some 18 gauge or 16 gauge. 20 gauge is very small for a 3kW oven. Typically 120 V ovens are limited to about 2000 W or so. Mine is 2100 W on a dedicated 20 A circuit. P.S . I am the guy who made the calculator. :)
     
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  3. Bluefish

    Bluefish New Member

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    I can do that, so what would I be shooting for with either a 16 or 18 gauge, what lengths?
    I don't mind a slow oven, just need to know what I need. This is where I fall short!
    Yes I knew you were the guys and thank you for share your experience and info!
     
  4. dancom

    dancom Dust Maker Best Shop Tool

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    I guess I should clarify. The smaller the wire gauge the higher the resistance per foot and this means less wire is required to achieve the desired resistance. Smaller wire also runs onto issues at high currents, where it acts like a fuse and burns up.

    I don't have the Excel sheet handy, but try some 16 gauge at 120 V, 3kW and 2 elements. Your elements should be long enough for coverage on both walls.

    Dan
     
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  5. dancom

    dancom Dust Maker Best Shop Tool

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    Do you have 240 V in the shop? I made mine around a 20 A circuit, which maxes out at 120 V x 20 A = 2400 Watts. A 120 V 30A circuit and tops out at 3600 W, but the breaker, receptacle and plug are not as common to source, heavier wire etc. 240 V supply has many advantages.
     
  6. Bluefish

    Bluefish New Member

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    No I do not have 240v in my shop yet, working on to that now. Need a 125 foot trench and 150 of wire. The trench is a lot cheaper then the wire.... lol
     
  7. Bluefish

    Bluefish New Member

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    I could always build it around 240 and just use my drier plug in the house for the time being. Not handy but doable.
     

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