Commercial Heating Elements
Heating elements - NiChrome Coils or Ribbon, Calrod, Quartz
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 heating element.
There are 3 basic types of heating elements. Nearly every appliance on the face of the planet will use one of these:
- NiCr 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. NiCr 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.
NiCr 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 NiCr 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).
- Sealed Element: This encloses a fine coiled NiCr 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 NiCr 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.
- 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.
Repair of Broken Heating Elements
In appliances like waffle irons and toaster ovens, these are usually welded. This is necessary to withstand the high temperatures and it is cheap and reliable as well. Welding is not normally an option for the do-it-yourselfer.
Use nuts and bolts, say 6-32, bolt, wire, washer, wire, washer, lockwasher, nut. Depending on how close to the actual really hot element it is, this may work. If you are connecting to the coiled element, leave a straight section near the joint - it won't get as hot. The use of high temperature solder or brazing might also work.
The best approach is probably to use high temperature crimp connectors: You can connect heating element wires with high-temperature solderless connectors that are crimped onto the wires. Be sure to get the special high-temp connectors; the ordinary kind will rapidly oxidize and fall apart at high temperatures. If you want to join two wires to each other, you'll need either a butt splice connector (joins the wires end-to-end) or a parallel splice connector (the wires go into the connector side-by-side). To fasten a wire to a screw terminal you can use a ring or spade connector. If your waffle iron has quick disconnect terminals you'll need the opposite gender disconnect. These come in both .187" and .250" widths.
Your best bet for getting these connectors in small quantity is probably a local appliance parts outlet that caters to do-it-yourselfers. High Temperature Barrel Terminals in several styles: ring, spade, disconnect, and butt splice. Be sure to determine the wire gauge of your heating elements so you can get the right size terminal.
You can spend a *lot* of money on crimp tools, but for occasional light use you can probably get by with gadgets that crimp, strip & cut wires, and cut bolts.
The thin stainless steel strip found spot welded to multicell NiCd batteries make good crimps for joining breaks in heater resistance wire. Form a small length of this strip around a needle or something similar to make a tight spiral with enough clearance to go over doubled-up heater wire. Abraid or file the cut ends of the broken wire. Crimp into place with a double lever action crimper. If there is an area of brittle heating element around the break then cut out and splice in a replacement section with two such crimps.
Another old trick for NiCr heating element repair is to make a paste of Borax, twist the two broken end together, and energize the circuit. A form of bond welding takes place.
Here's a "quick fix" that sometimes works for a long time and sometimes fails quickly (depending, I think, on just how old and brittle the nicr alloy wire is). Mix some ordinary "Boraxo" powdered hand soap with a little water to make a thick paste -- and you don't need much.
Take the broken ends of wire, bend a small loop into each, and interlock the loops so the wires stay together. Pack the Boraxo paste around the joint, and turn on the heater. Keep your eyes on that joint. As the coil heats up, the hook joint will be the worst connection, so it'll naturally get the hottest.
When it gets hot enough, the nichrome wires will melt, and, being fluxed by the borate, will fuse together into a blob. The blob, now being *larger* than the rest of the wires, will immediately cool down, and will never again get as "red hot" as the rest of the heater. Allow the coils to cool down and, using pliers, carefully crush any glassy flux deposit that remains on the joint.
If the joint doesn't behave as I describe, or if the wires are too brittle to be formed into hooks, the wires are likely too old to produce a long-lasting joint. If the joint behaves as I described, it may last for a good long time.Article courtecy of Repair FAQ @ Dr Exel