Fagor, Brandt - Induction hobs - working – error codes – troubleshooting - electrical connection

There are two techniques of glass-ceramic heating:
* The infrared.
* The induction.
These glass-ceramic hobs are as like as two peas.
The difference is only obvious once hobs are turned on.
The infrared one glows red while the induction doesn’t seem to operate.
The first is provided with radiant or halogen sources that transmit heat by radiation and conduction.
The second feeds a magnetic source, an inductor, which is placed under the glass-ceramic surface and transforms the magnetic energy into heat.
The traditional electrical hotplate is based on thermal conduction, while induction is based on the principle of the electromagnetic field.
The principle of heating by induction is a natural phenomenon discovered in the 19th century by several physicists, among whom Léon Foucault. He highlighted the development of currents facing the magnetic field in a moving metallic mass or a fixed metallic mass run through by a variable magnetic flux. These eddy currents in comparison to short-circuits cause a heating effect (Joule effect) in the mass.

Only since the middle of the 20th century induction started being used as a heating means, mainly in industries like the steel (induction furnaces). Induction only found its place in kitchens in the 80s, or even 90s for domestic electrical appliances with the marketing of the hob named IX1. The IX2 generation followed in 1992, IX3 (1996), IX3WR (2000) and currently IX4000 (2002) and IX6 (2005) generations.
The operating principle is innovating. Contrary to other cooking modes, it is the container itself, which heats and not the hob.
You put a saucepan down and this is sufficient to initiate the heat while the hob remains cold. The heating element is nothing but the container metal, which transforms the magnetic energy into thermal energy.  Induction qualities are flexibility, low inertia, easy cleaning, good efficiency and thermal safety.  Induction enables a litre of water to boil in two minutes, milk to heat without overflowing and chocolate to melt just as desired. Induction efficiency may reach up to 90% according to the types of cooking.
With such a technique, only the container heats. Inertia is therefore low and, above all, the plate temperature never exceeds the saucepan temperature.  Stepping from the mildest temperature to the strongest power, in an instant and while diffusing heat in a homogeneous way.
This technology is incomparable to those of present due to the induction method.

Operating principle

An induction hob operates due to the electromagnetic properties of most containers used on traditional hobs.  One can compare this hob with a transformer of which the secondary winding would have been shorted. A significant internal current arises therein and causes quick heating.

The saucepan can be compared with a shorted set of concentric whose internal resistance is not zero.  From the function keys, you control the electrical power supply to the transformer primary winding which generates a magnetic field. This field induces currents at the bottom of the container placed on the hob. These induced currents heat the container immediately, which transmits the produced heat to the food inside. Cooking is performed efficiently with almost no loss of energy. The appliance heating power is pushed to its maximum.

Skin effect

An induced current in a metallic mass will only cause significant heating if it flows through a significant resistor (P=RI2). A ferrite saucepan has only low resistivity. This is where a second natural phenomenon occurs, which is called ‘Skin effect’.

The propagation of the high-frequency current is not performed in the same way as a direct current.  Contrary to direct current, where current flows with consistency in a conductor, in HF its density varies and decreases exponentially as you move away from the conductor surface.

The current flows predominantly in wire periphery. The decrease in the effective cross-sectional area of the conductor causes an increase in its resistance.

At a 20KHz frequency, and for a steel saucepan (magnetic ferritic material), the thickness of the saucepan in which the induced currents flow is approximately 35 µm. This allows generating a current in only a part of the saucepan bottom. The resistance becomes significant and the heating consequent therein.

For a non-ferritic material, such as aluminium, the thickness is approximately 590 µm, the saucepan behaves then as a quasi-zero resistor (short-circuit), which is prejudicial to electronics. The board will take this discrepancy into account and will display the phenomenon by making the control panel flash. Therefore, this type of material is not adapted.

The efficiency is the ratio that exists between consumed energy (gas or electricity) and energy converted into heat. Large differences exist between induction, range-top appliance, and other cooking modes. These efficiencies may vary depending on the diameter and quality of the container used.

Removing the container from a source is sufficient to stop the cooking immediately, there is no energy waste. As long as there is no container on a source, the source does not heat, the power indicator lights are flashing. This hob consumes thus much less energy than hobs fitted with traditional gas or electricity hobs.

Electrical connection

Hobs with three or more sources have five wires to be connected. Wires other than the yellow/green shall be connected in pairs to a 32 Amp connector (connector specific for cooking).
Hobs loosely fitted, with connecting block or combined with gas can be connected to a 16 A connector (Conventional connector).

If the user has three-phase power supply, the connection can be distributed over two phases by separating the black wires of the 5-way cord.  The advantage is to work only with a 16A protection.

On hob power-up or after prolonged power cut, a luminous code is displayed on the keyboard. It disappears automatically after 30 seconds, or from the first action on any one key on the keyboard.

Temperature limiter
Each inducer uses a NTC sensor measuring the container temperature through the glass. This system help protecting the hob and the containers against over heating (Pan without food for example).  In case of overheating, the temperature of the pan is regulated around 300°C. This temperature does not allows the deterioration of the PFTE (anti sticking material used in the pans).Damages start above 340/350°C.

Glass ceramic is a silicium-based material that does not expand like glass. Its dimensions do not practically vary up to 750°C, as a part of the molecules composing it expands under heat, while an equal number retracts. A feature of this material is that it is a poor heat conductor and therefore limits heat loss.

The plane surface of the glass ceramic and the sensitive controls make cleaning easy. The own cleaning difficulties of radiant and halogen sources are usually groundless on induction hob, owing to the low temperatures attained by the table. However, a saucepan with humid bottom put on the source leaves limestone traces. Sugar discharges should be cleaned immediately, as in contact with hot glass ceramic the sugar caramelizes. When cooling down, it retracts and attacks the coating. Lastly, the glass-ceramic hob is not a working plane and thus is easily scratched.

Power supply

To supply the inducers, it is necessary to apply a high frequency. To change over from 50Hz to 50KHz it is first necessary to rectify the main voltage through a diode bridge. A filtering capacitor (of 5µF generally) is associated in order to attenuate the high-frequency signals. As shown by the illustration, the rectifier output voltage is approximately the main peak voltage (i.e. 310 VDC approx.) when no inducers are supplied. This voltage drops during the operation.

The inverter is used to transform a DC signal into an AC signal with adjustable frequency. The inverter consists of two transistors (whose technology can vary according to the hob generation), two capacitors and two recovery diodes (indispensable on any inductive circuit).  Transistors are frequency controlled by a generator. This frequency varies between 25KHz (for 2800W) and (50KHz for 500W).

Control

The entire operation is managed by a microprocessor.
* On generation IX1, a specific board performed the control; the power was managed by another board.
* On generation IX2, these two boards have been soldered and have become indissociable.
* On generations IX3, IX3WR and IX4000, power and control are entirely associated. So, the board integrates: A 5 and 12 VDC clipping power supply (which is also the keyboard power supply),  the control part (in liaison with the control keyboard), the rectifier part, the inverter part, and lastly, for board IX4000 and IX6, the filtering part.

The error codes
'Error' codes are a precious aid to diagnostic. Take care to well identify the model to be troubleshooted, as codes do not always have the same meaning.

The test keyboards
During a diagnostic, it is necessary to know whether it is the control keyboard or the power board, which is defective.  However, you must not omit the filter board, which includes two fuse pads and the power supply relay. Generations IX3 on the one hand and IX3WR, IX4000, IX6 on the other hand do not use the same encoding process. It is therefore advisable to be provided with two different test keyboards.
* IX3 keyboard: 79X5460
* IX3WR, IX4000 and IX6 keyboards: 79X9920
This keyboard will enable all the keyboard of each range to be replaced.  In event of degradation with use, base plates can be replaced:
* 6-point base plate (IX3) : 79X5461
* 8-point base plate (IX3WR, IX4000, IX6) : 79x9921

In event of problem with power supply, it is advised to check:
* Whether 'fuse' pads are out of order
* Whether the power relay is controlled (12VDC)
* Whether the relay delivers 230VAC to the board.
* Whether the relay delivers 230VAC to the fan.

Measurements on IX3 power board
These test points are used to check whether the independent filter board
* delivers a voltage for the control supply
* delivers a voltage for the power supply
* power relay is controlled by the command.

Measurements and checks on IX3 WR power board
These test points are used to check whether the independent filter board
* delivers a voltage for the control supply
* delivers a voltage for the power supply
* power relay is controlled by the command.