In this post we learn how to build a simple plasma globe or a plasma ball circuit using very oridinary parts such as an automotive ignition coil, a triac, diac, and a few other passive elements.
A plasma ball is a decorative display device in which a very high voltage in the order of many kilovolts is passed inside a glass ball, which results in the generation of a fascinating high voltage ionized plasma light display inside the glass ball
In our plasma ball circuit, an ordinary 100 watt bulb is used for the display unit. The glass lamp used in this design is customized by gluing a small sheet of aluminum foil directly to the back half of the glass, to make a kind of high voltage capacitor.
The filament inside the lamp bulb works like one particular plate of the capacitor, the glass of the bulb acts like the dielectric, and the aluminum foil serves like the second plate.
The aluminum foil, which acts like the negative plate of a polarized electrolytic capacitor, needs to be grounded by connecting the aluminum foil with the negative line. A high voltage is discharged inside the bulb by means of its inner filament electrode, ionizing the thin gas that stays within the glass envelope, producing a spectacular visual effect identical to an electrical lightening and storm.
The plasma ball or plasma Bulb circuit makes use of a triac diac combination, in which the diac acts like a trigger element and controls the current to the triac.
The main part of the circuit is an automotive ignition coil, T1, wired to supply a high-voltage charge of considerable power to ionize the gases present inside the glass of any ordinary incandescent lamp.
The entire circuit is powered directly the mains AC input.
The mains AC is supplied to the triac/diac stage via a phase-shift circuitry (which includes capacitor C1 and resistor R1) so that the triac is able to fire through the diac.
The moment TR1 fires or conducts, a small burst of electricity is driven through C2 to the primary side winding of T1. (Remember that as soon as AC mains input is first applied to the capacitor C2, it behaves like a short, after which the capacitor starts to charge towards the applied voltage level.)
This burst of electricity induces a strong rush of magnetic field inside the T1 primary winding, triggering an equivalent amount of stepped-up high voltage across its secondary winding of the ignition coil.
Next, as soon as the capacitor C2 starts to charge to its maximum peak level, the AC voltage to the diac begins to drop quickly. As the voltage drops downwards, the current necessary to keep triac switched ON sinks below the holding level, the triac now gets switched off.
After this positive cycle, the next half of the AC signal which is negative commences.
As the AC voltage cycle starts getting more negative, a potential begins appearing to the triac's trigger input via the diac, triggering it to fire. Since triacs are designed to conduct for both the AC half cycles, the triac fires during both the voltage cycles of the AC.
Now as TR1 conducts in the reverse direction, the C2 charge begins draining off, via TR1, which causes the next burst of electricity with opposite voltage to get induced in the primary winding of T1, causing the equivalent amount of stepped up voltage to be transferred in its secondary winding.
During these conductions of the triac, high-voltage output of more than 2 kv is generated at the secondary of T1 which is applied to the lamp, filament, creating a plasma ball display to be generated inside the lamp.
The C2 value should be selected such that it is not beyond 2-2.5 µF to protect against damage to the ignition coil T1.
Alternatively, if the C2 value is selected very small, the plasma ball sparking inside the bulb might fail to glow with satisfactory effect and brightness.
Inductors LI and L2 have been included in order to block the ignition coil switching transients and spikes from returning back to the home AC wiring or the AC line.
Plasma Ball Cabinet
The enclosure for the above explained plasma ball circuit can be fabricated in the following manner, using wooden box, or plastic box and tubes.
Do not use metal box or tube for the cabinet, since the whole set involves high voltages and mains AC input which can lead to electricity shocks or other electricity related accidents.
The aluminum foil behind the glass bulb is not shown in the above image, so make sure to stick an aluminum foil behind the bulb glass externally and connect it wire it with the circuit appropriately as per the indicated diagram layout.
Once the above set up is built and tested, do not forget to cover the lamp structure with another plastic tube, so that the glass can e protected from accidental knocks and damages, as shown below:
The ignition coil can be any automotive ignition coil, preferably the one that are used in motorcycles. The following image shows an example motorbike ignition coil which could be used for the above explained plasma ball circuit:
WARNING: THIS PROJECT INVOLVES EXTREMELY HIGH LETHAL VOLTAGES. USERS ARE ADVISED TO MAINTAIN EXTREME CAUTION AND TAKE APPROPRIATE PROTECTION MEASURES WHILE BUILDING AND TESTING THIS CIRCUIT.