You can use any heating elements that the voltage regulator you have can control. Here we look at the most common type of heating element.
In Russian, the abbreviation ТЭН (heating element) stands for "tubular electric heater". So the assembly contains as many heaters as it has tubes. If you divide the total power of the heating element by the number of tubes, you get the power of one tube. All tubes have the same power.
As a rule, a 3 kW model is chosen. Each tube then has a power of 1 kW. For 1.5" columns this is a good choice, because to run in pre-flooding mode a column 1.5 meters high needs 1.2-1.4 kW of power. That leaves a power reserve.
So you can use a combined connection:
Connect two tubes through the regulator; this gives 2 kW. During rectification the regulator keeps the output voltage within 170-180 volts. That is quite enough, even when the mains voltage "sags".
Connect the remaining tube through a solid-state relay, and control that relay through the contacts of relay No. 4. This will be the boost heating element.
For 2" columns, a 3 kW heating element is not enough with this wiring scheme. A 4.5 kW element is just right.
By switching the tube connections you can use much more powerful heating elements, and they will run in a gentler mode. Of course, follow the principle of reasonable sufficiency.
Below is a table of possible heater connections in the assembly.
How to read the table, using a 4.5 kW heating element as an example
In the left column, select the power - 4.5 kW. The top row, by number, shows the heater connection scheme.
For example, number 1 is a series connection of all three heaters. At the intersection of the row and column is the power the assembly delivers when 220 volts are applied to it = 0.5 kW, or just 500 watts.
Connection No. 6 gives 3 kW on 2 heaters and leaves one heater unused - so it can be used as the boost heating element.
