Travel Water Heater

Dear people — in the past few years, I have gone through about seven of those spiral immersion water heaters that operate from 12 V DC. Most of them didn’t even last as long as a trip by car to and from the south of France. After a bit of experimenting with resistors, incandescent lamps and other electronic components that can give off heat and might be able to last longer than these immersion-type travel water heaters, I found the answer in the form of the trusty 2N3055 transistor in its TO- 5 package. It has a maximum operating temperature of 200 °C and a maximum rated dissipation of around 115 watts. The power level can be set with a single resistor between the collector and the base, so the circuit consists of just two components aside from the cable and plug. The advantage of using a 2N3055 is it is available everywhere and is very cheap. A disadvantage is that the gain is terribly low, and on top of that it varies widely from one device to the next. This means that that the resistance value must be determined for each transistor individually, and there is a good chance that the resistor will become fairly hot. If the 2N3055 is biased to dissipate 50 W and it has a DC gain (hFE) of 20, for example, the resistor will dissipate 2.5 W. The solution to this problem is to select a transistor with high hFE or use a Darlington pair.

Drill four holes in the bottom of a water jug: two for the fixing screws and two for the base and emitter leads. Fit a thin layer of silicone rubber (cut from a silicone baking cup or baking mould) between the mating surfaces of the transistor and the bottom of the water jug. This material is suitable for use in contact with foods and beverages, and it can withstand temperatures up to nearly 200 degrees Celsius. The chromium of the 2N3055 package also appears to have no harmful effects on health, since immersion heaters are also chrome-plated. Based on experience, the silicone rubber provides an adequately water-tight seal. Fit the bias resistor under the bottom of the jug, which will have to be fitted with small feet for this purpose. My 2N3055 heater has been working well for some time now, and I’m free of the problem of burnt-out immersion heaters. The silicon of the 2N3055 can obviously take the heat better than the material used to make the heater wires. This principle can also be used for an aquarium heater or any other device where a liquid has to be heated to a certain temperature. In addition, you can use a temperature sensor to control the dissipation of the 2N3055 by regulating its base current and thus keep the liquid at a specific temperature.