Nail Melter / Spot Welder

The secondary circuit carries 50-100+ amperes. Never touch the secondary circuit or nails while energized. Turn off power before adjusting.

The nails remain dangerously hot even after they stop glowing. Do not touch for several minutes after use. Molten metal droplets may be ejected during sparking.

Do not hold nails in contact for more than 5–10 seconds. Allow at least 30 seconds between cycles to avoid overheating the secondary coil and transformer.

Bright sparks and metal spatter present eye hazards. Maintain adequate distance from the audience or use a transparent shield.

Purpose

A step-down transformer with a 250:5 turns ratio produces extremely high current at low voltage. Squeezing nails together produces dramatic sparking and incandescent heating, vividly demonstrating $$P = I^2R$$ dissipation and the inverse relationship between voltage and current in transformers.

Demountable transformer on wooden base with 250-turn primary coil (left) and 5-turn copper helix secondary coil, connected to wooden-handled nails producing bright sparks at contact

Nail heads held in contact glowing orange-hot from resistive heating, with the demountable transformer visible in the background

Figure 1: Quickly tapping the nail heads together produces a shower of sparks. The 250-turn primary coil (left) and 5-turn secondary coil (copper helix) form a step-down transformer producing high current at low voltage.

Figure 2: Holding the nails together for several seconds causes them to glow incandescent from $I^2R$ heating.

Danger: High Current Electrical Hazard

Warning: Extreme Heat Hazard

Warning: Continuous Operation Warning

Warning: Eye Protection

Purpose

Safety Warnings

Danger: High Current Electrical Hazard

Warning: Extreme Heat Hazard

Warning: Continuous Operation Warning

Warning: Eye Protection

Purpose