12 Volt Fluorescent inverter for 20 - 40 Watt tubes

  
This is a low-cost project for 20 or 40 watt fluorescent tubes. However the most efficient is to use a 40 watt tube (or two 20 watt tubes in series). It's a circuit you can put together from junk box components or build from a kit. It's very simple to build and requires no printed circuit board. The transformer is hand-wound on a ferrite rod (from an old transistor radio) and the winding wire can be salvaged from an old transformer. The ferrite core of the transformer is an antenna rod from an old transistor radio. You could use a slab antenna but we have chosen a 10mm diameter rod, 8cm long and the first winding to be wound on it is called the primary. We are purposely keeping costs down to show how cheaply it can be put together.
12 Volt Fluorescent inverter for 20 - 40 Watt tubes - schematic

Depending on your stock of parts, the cost could range from $3.00 to about $15.00 and if the wires from the transformer are soldered to the ends of the tube(s), you can create a free-standing light that can be set-up in the garden to illuminate a dark area without the fear of running 240v wiring. The cost of powering the circuit is about 22 watts and this will produce the same light output as a 60 watt globe. With a normal fluoro operating on the 240v mains, a ballast (or choke) is needed in series with the tube to limit the current after the tube has "struck". This ballast dissipates about 10-20 watts for a 20 watt tube and reduces the efficiency of the circuit. If the ballast is replaced with an electronic circuit and high-frequency transformer, the losses are less than 5 watts. Furthermore, if we do not drive the tube as hard as the 240v version we can get even better efficiency. The size of tube, you will need, will depend on the area you wish to illuminate and the battery capacity you have available, however it is important to realise that the higher wattage tubes offer the greatest efficiency. This is because they have a longer length and larger diameter (than say an 8 watt tube) and give more light over a larger area. That's why we have concentrated our design on the 40 watt tube. You can get plenty of circuits and devices that power the 4, 6 and 8 watt tubes but nothing has been done for the 40 watt variety....



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