The Compleat Distiller

THE COMPLEAT DISTILLER 48
Heat control is also relatively easy with indirect heating methods, particularly the water jacket. In this
case, you are concerned with the temperature of the circulating fluid, not the heater element itself. The
large volume of circulating fluid smooths out the fluctuations from the heater.
Most consumer equipment (electric soup kettles, frying pans, etc.) has adjustable thermostatic control,
which will not be satisfactory for a boiler, but can work as a source of indirect heat. If you are using
this kind of equipment for a direct boiler, you need to lock the thermostat on high and use another
means of controlling the heat output.
Methods of control that work well for isolated or concealed elements may produce problems with an
immersed one, because there is no heat buffer between the element and the boiling liquid. It's
surprisingly difficult to evenly control the output of a simple electrical heater element. Many ingenious
methods have been tried, but most of them cannot be recommended because they can interfere with the
power supply system by inducing spurious direct currents into the "neutral" line. These currents can,
and do, cause major power supply fluctuations that can lead to area blackouts and expensive repairs.
Recent (January 1, 2001) international regulations are quite explicit about this this and related radio
frequency interference*.
These regulations have become necessary because of the cumulative effect of all the ordinary pieces of
electrical equipment that people use daily – light dimmers, fan speed controls, heater controls, etc.
The sheer quantity of such equipment is now so large that what used to be a minor problem has grown
to major proportions.
It is important that any heater control you use doesn't contribute to this, because one boiler on its own
can have as large an effect as 100 other devices. Power companies are now actively searching for large
sources of interference − and a poorly controlled boiler would be a large source. DO NOT attempt to
control a large power heater element with an ordinary light dimmer, no matter what its rating.
Dimmers rely on phase switching and not only introduce direct currents into the neutral line, they also
introduce multiple harmonics of the basic power supply frequency. Both these effects can damage the
power supply system. Even switching a heavy load on and off rapidly without sophisticated phase
control can cause damage. For this reason, don’t use the old method of using a diode to halve the
power delivered to the boiler. It will interfere with the power supply and the power company will
come looking for you.
You can find the design of a control circuit in Appendix 5. This circuit is designed to be fully
compliant with current regulations.
We must stress that only people who have experience with electrical circuits should attempt to build
any of the devices mentioned in this section, because large currents are involved. If you have any
doubts at all about your skills in this area, find a friend who has sound electrical experience and get him
or her to make it for you.
* International Electrotechnical Commission (IEC) regulations:
IEC/EN61000-3-2
phase control of power
IEC/EN61000-3-3
creation of rapid voltage changes
CISPR 14-1/EN55014
radio interference relating to household appliances