Calculations

NiChrome

 

This page contains all of the technical data for NiChrome Wire.

Reference the Electrical Power Section to calculate necessary requirements for

your power supply.

DIAMETER - The smaller the wire, the higher the resistance per foot

    - As the diameter increases in size (AWG decreases) the resistance decreases

Obverse : As the diameter decreases (AWG increases) the resistance increases

    - It is easier to move an electrical current through a large wire, than it is a small wire


LENGTH - The longer the wire, the higher the over all resistance

    - As length increases, the resistance increases

Obverse : As the length decreases, the resistance decreases

    - The more wire you have, the more resistance it creates

Notice that as the wire diameter gets smaller (higher gauge wire) the resistance per foot increases.

In the following table there are Amperage ratings required to heat NiChrome wire to a specific degree.

General Information

NiChrome Wire is composed of Nickel & Chromium.

NiChrome Wire is the optimal wire choice for foam cutters for a variety of reasons, but particularly because it is resistant against corrosion and oxidation at very high temperature.

There are two readily available types of wire, NiChrome A & NiChrome C

    - Nichrome A contains 80% Nickel and 20% Chromium

    - Nichrome C contains 60% Nickel, 16% Chromium, & 24% Iron

By comparison, there isn’t too much different between the two wires with the exception of the following

    - Nichrome C has a little higher resistance per foot

    - Nichrome C increases more resistance per foot as temperature increases

    - Nichrome A has higher tensile strength

    - Nichrome A has a higher melting point

Based on this information it would appear that NiChrome A is better to use, but as it stands NiChrome C is a bit easier to acquire and a bit cheaper. But practically speaking, there is not much functional difference between the two when it comes to cutting foam.

Principles of Application

Before you attempt to calculate your power supply requirements, it is crucial that you determine the resistance of your circuit. It is this resistance that has a direct impact on how much voltage and amperage you require to heat the wire to a cutting temperature

All NiChrome Wire has a rated resistance which is measured in Ohms Per Foot and is based upon the Length & Diameter of each wire. 

The wire diameter is classified by the American Wire Gauge Scale (AWG). Information regarding actual millimeter and inch diameter is also available, but the AWG scale is the easiest platform for discussion.

For reference

The smaller the AWG, the larger the diameter

10 gauge = 0.102 inch diameter, 40 gauge = 0.0031 inch diameter

Straight Wire Cutters

26 Gauge NiChrome Wire Chromel C

Rigid Wire Cutters

20 Gauge NiChrome Wire Chromel C

26 gauge wire is the best all around candidate and is very versatile.

It has a perfect balance of tensile strength and energy requirements, making it ideal for not only cutting but also fits the capabilities of most power supplies.

Some users prefer stepping up to a bit larger wire at 24 gauge because it is a bit more stiff. When the wire is used over a longer span (over 2 feet) sometimes the extra rigidity is nice to prevent bowing while cutting. The trade off is by having a larger wire, you require more amperage to heat the wire which may mean a more expensive power supply.

For some, they require a wire that can be bent and shaped to make interesting designs, carve rivers, mountains, and more!

24 & 26 gauge wires are simply not stiff enough to hold any shape, but as you start to increase the overall diameter of the wire (meaning the gauge number decreases) your power requirements begin to increase.

With a very stiff wire like 10 gauge, it will practically hold any shape you bend it to, however, the amperage required to heat it to around 700 degrees is much higher than most inexpensive and readily available DC power supplies.

A very well known online retailer and manufacturer of rigid wire foam cutters uses 20 gauge wire because its energy requirements are much lower, and it is still very stiff and rigid when bent. If its good enough for them, its good enough for me!

When selecting a cutting temperature, for most foam products a good temperature is around 600°F / 315°C

_NiChromeData_files/NiChrome%20Data.pdf
_NiChromeData_files/NiChrome%20Data_1.pdf
CLICK HERE_NiChromeData_files/NiChrome%20Data_2.pdf

PDF available for download

Wire Resistance

HEAT - More heat, more resistance

    - The more heat that the wire generates, the more resistance it will create

This chart represents the percentage of increase resistance with relation to wire temperature

Generally speaking, for the application of a Hot Wire Foam Cutter, this really does not matter.

Current Rating

Before a power supply can be purchased, you need to determine the current / amperage necessary to heat your NiChrome Wire.

Know that it is the CURRENT not the voltage nor the wattage that heats your wire. Rather, it is the actual passing of current through the wire that ultimately determines its temperature.

The VOLTAGE is the electrical driving force behind the current. And it is the resistance of your wire that determines the level of voltage required to obtain your desired current.

The WATTAGE is simply voltage multiplied by current. This rating is typically provided when determining if the power supply can handle the output power.

Most foam products, 600°F / 315°C should be more than enough.

For instance, 26 gauge requires 2.14 amps to heat to 600°F, but 2 amps should be adequate as well.

Wire Recommendations
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