Building a miniature Tesla coil that can fit in your pocket is a fun electronics project that allows you to experience high voltage electricity on a small scale. With some basic electronic components, wire, and tools, I was able to construct my own pocket-sized Tesla coil that can wirelessly power small neon bulbs.
What is a Tesla Coil?
A Tesla coil is an electrical resonance transformer designed by the inventor Nikola Tesla in 1891. It is used to produce high voltage, low current, high frequency alternating current electricity.
The two main components of a Tesla coil are:
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Primary coil - Made of a few turns of heavy gauge copper wire around a cylindrical form. This coil is connected to a high voltage power source.
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Secondary coil - Made of hundreds or thousands of turns of fine gauge wire wound around the primary coil. Through resonance, this coil transforms the low voltage, high current power from the primary into high voltage, low current power.
The alternating current in the secondary coil charges the terminal at the top to extremely high voltages of ~100,000 volts or more. This voltage ionizes surrounding air molecules causing the dramatic corona discharge and arcing that Tesla coils are known for.
How a Miniature Pocket Tesla Coil Works
A miniature pocket Tesla coil works on the same principle as a full size Tesla coil but is much smaller and designed to run on lower voltages.
The key components I used to build my pocket Tesla coil are:
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12V DC power source - A 12V battery pack or wall adapter
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Oscillator circuit - An electronic circuit to convert the DC into high frequency AC. I used a common 555 timer chip.
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Drive coil - The primary coil made of just 2-3 turns of 16 gauge magnet wire.
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Resonance coil - The secondary coil made of 400 turns of 36 gauge magnet wire.
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Topload - A terminal on top of the secondary coil made of a toroid of wire. This shapes and enhances the electrical discharge.
The oscillator circuit converts the 12V DC into pulses of high frequency AC electricity at ~500 kHz. This oscillating current is fed into the drive coil which induces a magnetic field in the resonance coil.
At its resonant frequency, the voltage in the resonance coil builds up through each cycle of the AC power to around 5-10kV. This ionizes the air at the topload terminal creating corona discharges and arcs.
Constructing the Coils
The most important step in constructing a miniature Tesla coil is building proper primary and secondary coils with the right number of turns and diameter.
To make the primary drive coil:
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Wrap 2-3 turns of 16 gauge magnet wire around a 1.5" diameter PVC pipe.
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Leave about 6" wire leads on each end.
To make the secondary resonance coil:
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Wind 400 turns of 36 gauge magnet wire around the drive coil form.
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Use tape to secure the ends.
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Leave about 6" leads on each end.
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Carefully slide the coil off the PVC form.
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Spread the turns evenly spaced over 2-3" length.
The resonance coil should have an inductance of ~1mH. I measured the inductance with a multimeter to fine tune the number of turns.
Constructing the Circuit
The oscillator circuit provides the high voltage AC current that drives the Tesla coil. I built mine around a NE555 timer chip:
To build the circuit:
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Solder the 555 chip and other components onto a prototyping circuit board.
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Connect the drive coil leads to pins 3 and 4.
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Power with a 12V source on the input pins.
Tune the frequency with the variable resistor to find the resonance point of the secondary coil, indicated by maximum brightness of discharge. Around 500kHz works well.
Adding a Topload Terminal
The topload shapes and enhances the electrical discharge at the terminal of the secondary coil.
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Form a 1.5" diameter toroid out of 12 gauge copper wire.
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Solder one end of the resonance coil to the bottom of the toroid.
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Leave a 1" gap between the toroid topload and coil.
Testing it Out
Once assembled, connect your 12V power source and enjoy the plasma light show!
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Bring a grounded metal object near the topload to generate corona discharges.
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Hover fluorescent bulbs near the terminal to wirelessly power them.
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Adjust circuit components to maximize discharge intensity.
With some careful winding, tuning, and tweaking, your pocket Tesla coil will be electrifying! Just be very cautious, as the high voltages involved can be dangerous.
Building a DIY Tesla coil that fits in your pocket is an extremely fun electronics project that lets you experience high voltage electricity firsthand. The construction process teaches valuable skills and the end result is a conversation piece that impresses any crowd. Just be sure to follow proper safety precautions when operating your handheld high voltage generator!