An electric soldering copper uses a resistance heater to warm a copper bit, which carries heat toward its working face. This cutaway shows the bit, insulated winding, protective shell and handle. A separate dimensioned conductor explains the calculator, which estimates ideal axial conduction and compares positive heat demand with an entered heater rating.
Electric Soldering Copper Interactive Calculator
Explore an early electric soldering copper and a dimensioned ideal conduction model. Compare the signed heat flow with an entered heater rating.
Equation Used
- Uniform square section and steady one-dimensional conduction.
- Constant conductivity 400 W/(m·K) and prescribed end temperatures.
- No taper, interface resistance, heat storage or solder-melting model.
- Heater power comparison excludes thermal losses and control behavior.
Uniform square conductor, fixed endpoint temperatures and no contact or heat-loss model. Not a heater recommendation.
Electrical heating and conduction through the bit
Hiscox movement 743 illustrates an early tool with a resistance winding around the copper, insulation, a protective shell and electrical connections passing through a hollow handle. The main cutaway follows that construction principle; it is not a modern temperature-controlled station or an assembly specification.
The tool parts remain still during operation. The lower animation instead shows the direction of heat transport through the ideal conductor. Its endpoint temperatures are supplied by the user, and colour indicates their relative values rather than a glowing metal surface.
A real working tip is tapered and may include coatings, while a real joint has a contact interface. The lower model deliberately separates those construction details from its assumption of a uniform square conductor. Modern plated copper tips and their interfaces cannot be reduced to this drawing alone.
Explore geometry and temperature difference
Enter a square conductor width, uniform heat-path length, temperatures at the bit-core and working-face ends, and the heater power rating used for comparison. Width represents both sides of the square cross-section, not an independently measured contact footprint.
The fixed conductivity assumption is 400 W/(m·K), an illustrative value for copper. Actual conductivity varies with temperature, alloy and construction. The calculation is conditional on that supplied material assumption.
Both dimensions appear on the lower model using one drawing scale. A wide short conductor looks different from a narrow long one. Changing either endpoint temperature changes the heat-flow result and can reverse its direction.
Steady one-dimensional conduction
Fourier conduction through a uniform section gives Q̇=kA(Tleft−Tright)/L. Here A=w², width in millimetres is converted to square metres, and path length in millimetres is converted to metres. The result is watts.
Positive Q̇ means heat flows from the bit core toward the working face. Negative Q̇ means the working face is hotter and the ideal flow reverses. Equal temperatures give zero net flow. The sign of the result identifies the direction of heat flow.
For comparison with heater rating P, define positive demand H=max(0,Q̇). The displayed power difference is P−H, the ratio is P/H when H is positive, and loading is 100H/P percent. When H is zero the ratio is not applicable.
The comparison does not include a sizing allowance. These comparisons do not establish a recommended heater size: real losses, thermal storage, contact and temperature control are absent.
Default conduction comparison
For a 3.2 mm square section, an 8 mm path, endpoint temperatures 380°C and 350°C, and k=400 W/(m·K), ideal conduction is 15.36 W. Compared with a 70 W heater, the positive demand is 21.94% of the rating, the ratio is approximately 4.56 and the arithmetic difference is 54.64 W.
Doubling width quadruples area and ideal heat flow. Doubling path length halves ideal heat flow. Swapping the endpoint temperatures reverses the heat-flow sign without changing its magnitude.
If ideal demand exceeds heater power, the difference becomes negative. In a real system the assumed fixed temperatures could not be sustained by that heater alone under this model; the calculator does not solve the new temperatures.
Why this is not a soldering-time prediction
The model assumes steady conduction, constant conductivity, a uniform section and fixed temperatures at both ends. It excludes heat stored in the bit and workpiece, air losses, solder phase change, coatings, oxidation, wetting and contact resistance.
The power difference is an arithmetic comparison before those missing effects. A positive difference does not guarantee thermal recovery, joint quality or suitability for a particular task. Endpoint temperatures are calculation inputs, not recommended soldering settings.
Dwell time, coatings, oxidation and heater performance depend on the particular tool and joint. A thermal transient or a measured tip-to-joint model is needed to predict an actual process.
Electric soldering copper questions
Why does the result become negative?
The working-face end is hotter than the bit-core end, so the entered gradient drives heat in the reverse direction.
Why is the heater ratio sometimes not applicable?
There is no positive outward conduction demand to divide into heater power, so the ratio has no applicable value.
Does tip width mean contact area?
Here it defines a square conductor cross-section, A=w². Actual contact area and contact resistance are not modeled.
Why is the physical tip tapered but the calculation block rectangular?
The cutaway identifies the real tool; the separate block makes the simpler uniform-section calculation assumption explicit.
Will a larger heater necessarily produce the entered temperatures?
No. The temperatures are imposed inputs. A real tool also depends on thermal losses, storage and control.
References
- Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), printed page 198, movement 743 — early electric soldering-copper construction.
- MIT Unified Engineering: Introduction to Conduction — Fourier conduction, cross-section and path length.
- HAKKO: Tip life — copper cores and plated working tips.
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