## Power supply

The packed column which will be mounted above the boiler (see later) has only a limited capacity to allow vapours to rise up through the packing against the downward flow of condensed liquid so the boil-up rate must not be too great or the column will choke (flood). The 1500 or 3,000 watt heater supplied with these boilers is, in fact, unnecessarily large and we need to reduce this wattage to about 750 in some way. Several methods for doing this suggest themselves. One would be to buy a 750 watt immersion heater from a manufacturer of heater elements but this would be costly and time-consuming. We are not even certain if a 750 watt immersion heater exists. Another would be to buy a step-down transformer, either fixed or variable, but this would be even more expensive. A very simple and inexpensive solution to the problem for residents of N. America is to buy a water heater with a 3000 watt, 240 volt element already installed and use it on 120 v. Or, if the boiler is fitted with a 120 volt element remove it and substitute a 3000 watt, 240 v. element. The voltage has been cut in half, which will cut the current in half, so the wattage will be reduced by a factor of 4, i.e. V2 x 1/2 = 1/4 and 3000 x V4 = 750 watts.

For the electricians among you another solution would be to carry out half-wave rectification of the electricity supply using a diode. This will cut the wattage in half. If you want continuous, variable control you could use a triac, but unfortunately the inexpensive household variety (a light dimmer switch) has a capacity of only 500/600 watts. A 1000 watt dimmer can be purchased for about \$40 (US) and a 2000 watt model for perhaps \$150.

You do not need to continuously vary the wattage input to the boiler and we recommend that you avoid this unnecessary complication and expense. Rather, arrange by one means or another to use the appropriate wattage for the column you are using (e.g. 750 watts for a 1 1/4" column) and stick to it. Incidentally, you do not need to measure either the temperature or the pressure in the boiler — the pressure is atmospheric and the temperature is the boiling point of beer, e.g about 100°C.