Mini heat coil

Discussion in 'The Projects Forum' started by james211, Jul 1, 2013.

  1. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    Does anyone know of a source that I could buy a small heating coil from? I'm looking for a coil that will not reach temperatures above 150 degrees fahrenheit.

    Basically I'm looking to build a small food dehydrator. I know I could use a lightbulb, as thats what most people do, but if I could find a small element of some sort I'd prefer that.

    The size of the final box will probably be around 10x10x10. I live in NYC and have limited space so I need to make my own.

    Let me know if you have any ideas.

    Thank you.
     
  2. #12

    Expert

    Nov 30, 2010
    16,354
    6,852
    A resistor will work, but everybody uses light bulbs because they are cheap, easy to find, resistors...and they accidentally make some light. You can calculate the resistance you need and buy a resistor that doesn't glow. Then compare the prices and the shipping cost. www.mouser.com, Digikey, Jameco, etc.
     
  3. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    Well my biggest concern is safety obviously. I'm open to trying it I just need to make sure I know how to mount it properly. Do you know of any tutorials?
     
  4. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    The better dehydrators have a fan to drive out the moist air, as well as heating the air. If you have access to an old hair dryer, you could use the fan and also run a lower current through the heater so it doesn't get as hot.
     
  5. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    I've actually thought about that. I have a nice bug 220mm comp fan I was going to use as they are a lot quiter. As far as the element from the hair dryer, how could I control how much heat it outputs? Ideally it would be variable....
     
  6. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    You would first need to check the resistance of the heater since it might have been connected to 110VAC. If so, the best way would be to use a thryistor to control the power through the heater. I haven't use one so I'm not exactly sure how to connect it up, but there are circuits available. This is probably a good place to start.
     
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,871
    1,394
    If your paramount concern is safety, you would be much better off using low voltage DC for the heater and the fan.
     
  8. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
  9. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    Why? It'd need to be carefully wound onto a mica backing or such and introduces a modest hazard. Lightbulbs are cheap and provide the nominal wattage with pretty good accuracy. If you need a small profile, look into cabinet lighting and such.
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    My American Harvest dehydrator uses a TRIAC (10A, 400V Q4010L5) under control of a thermistor and a variable resistor as a thermostat. It includes a 98°C thermal fuse (10A, G4A01098C), which I would highly recommend for any device like this.

    I had to repair it not long ago, and I may have drawn out the schematic. There's no isolation from the mains, so I'm reluctant to post it.

    [edit] There's also a fan that is always on when the unit is plugged in. Some portion of the air recycles (to retain heat) but a fraction escapes.
     
    Last edited: Jul 1, 2013
  11. Relayer

    New Member

    Jan 1, 2013
    18
    1
    You can always purchase a length of resistance wire, also known as Nichrome. Its resistance per meter is approximately 14 ohms.
    You could power it using a high current DC source rather than mains power.
    You can wind the wire into a coil using say, a long metal bolt to the length you require, then carefully removing it from the bolt.
    You can employ a current regulator circuit to vary the heat generated without drawing too much amperage.
    Regards,
    Relayer :D:D:D
     
  12. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,019
    1,542
  13. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,871
    1,394
    In principle, nichrome wire heaters are possible, but they are a little more complicated than they might seem at first glance. For example, their resistance is not a uniform 14Ω per meter; it depends on the wire diameter. In addition, the maximum temperature of the wire must be taken into consideration in order to avoid creating a skin burn hazard, a fire hazard, or a wire melt potential.

    Using a threaded bolt as a coil form is possible, but the length and diameter of the coil will dictate its ability to self-support. In a worst case, the wire coil sags to the point that all the coils are shorted together, the resistance approaches 0Ω, and the wire melts.

    Here's a document that gives a good introduction to designing heating elements with nichrome wire. http://www.cecs.wright.edu/balloon/images/2/22/Nichrome_Wire_Heating_Element_Design_Basics.pdf
     
  14. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,073
    3,856
    Nichrome must be crimped instead of soldered. Very fine sta-cons need to be used since the wire must be thin.
     
  15. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    You wrap the thin Nichrome wire around a stump of copper wire, and crimp that in the lug. ;)
     
Loading...