This is a cheap, robust and safe way to control electric heatings and save money by scheduling their operating range.
This is based on pilot wire technology
All recent electric heatings are equipped with pilot wires.
Step 1: Pilot Wire Technology : Main Principles
pilot wire is a third wire (hot wire, neutral wire and pilot wire) which is used to send electrical signals to the heating in order to switch its operating mode.
Basically there exists 4 operating modes (see diagram) :
* when no signal is sent to the heating, it works in COMFORT MODE
* when a sine (230 V) is sent, the ECO mode is triggered
* when a negative half-sine is sent, the heating switches to FROST FREE mode
* when a positive half-sine is sent, the heating stops.
Step 2: Hardware
You need very cheap supplies :
* one timer switch (<5$)
* one cable gland (<1$)
* one mini electrical switch (<1$)
* one 1N4007 diode (<1$)
and also soldering equipment of course
Step 3: Soldering Scheme
The first diagram illustrates the wiring scheme of the original timer switch before changes.
The idea is to control the pilot wire by the clock instead of the hot wire.
An additional mini switch is used to choose the ECO mode or the STOP mode for regulation:
if the ECO mode is selected, the heating switches from the COMFORT mode to the ECO mode, depending on the timer settings (time ranges are usually 15 ' wide).
If the STOP mode is selected (check the polarity of the diode to generate the positive half sine), the heating stops at given time periods (defined with the timer switch settings). The STOP mode is useful when several heatings works and no load-shedding is used. If all heatings operate at the same time, even in the ECO mode, the peak power needed may exceed the limitation of the electrical facilities.
Step 4: What It Looks Like
and it works fine and safe
NB : if heatings are not equipped with pilot wires do not try to control the hot wire itself. This way is not safe. At least it may alter the heating regulation unit, in the worst-case scenario it can cause fire damages.