Heating elements – NiChrome coils or ribbon, Calrod, Quartz

August 9, 2009

All heating elements perform the same function: convert electricity into heat. In this they have one other characteristic in common: they are all nearly 100% efficient. The only electrical energy which does not result in heat is the slight amount of light (usually red-orange) that is produced by a hot element.

There are 3 basic types of heating elements. Nearly every appliance on the face of the planet will use one of these:

  1. NiChrome coil or ribbon: NiChrome is an alloy of Nickel and Chromium which has several nice properties for use in heating appliances – First, it has a modest resistance and is thus perfect for use in resistance heating elements. It is easily worked, is ductile, and is easily formed into coils of any shape and size. NiChrome has a relatively high melting point and will pretty much retain its original shape and most importantly, it does not oxidize or deteriorate in air at temperatures up through the orange-yellow heat range.

    NiChrome coils are used in many appliances including toasters, convection heaters, blow-dryers, waffle irons and clothes dryers.

    The main disadvantage for our purposes is that it is usually not possible to solder this material due to the heating nature of its application. Therefore, mechanical – crimp or screw must be used to join NiChrome wire or ribbon to another wire or terminal. The technique used in the original construction is may be spot welding which is quick and reliable but generally beyond our capabilities.

    Testing: Visual inspection should reveal any broken coil or ribbon. If inspection is difficult, use a multimeter on the low ohms scale. Check for both shorts to the metal chassis as well as an open element (infinite ohms).

  2. Calrod(tm) sealed element: This encloses a fine coiled NiChrome wires in a ceramic filler-binder inside a tough metal overcoat in the form of a shaped rod with thick wire leads or screw or plug-in terminals.

    These are found in toaster oven/broilers, hot plates, coffee makers, crock pots and slow cookers, electric range surface elements, conventional and convection ovens and broilers.

    Testing: When these fail, it is often spectacular as there is a good chance that the internal NiChrome element will short to the outer casing, short out, and melt. If there is no visible damage but the element does not work, a quick check with an ohmmeter should reveal an open element or one that is shorted to the outer casing.

  3. Quarts incandescent tube: These are essentially tubular high power incandescent lamps, usually made with a quartz envelope and thus their name.

    These are found in various kinds of radiant heaters. By running a less than maximum power – more orange heat – the peak radiation is in the infra-red rather than visible range.

    Testing: Look for a broken filament. Test with an ohmmeter just like an incandescent light bulb.

http://repairfaq.ece.drexel.edu/sam/appfaq.htm#afbatheory
http://www.resistancewire.com/mainpage.php?page=techinfo

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