COMPONENTS
The heating of the cabinet is entrusted to the elements that surround the fan ,which with its rotation cools them and at the same time distributes the heat in the cooking cabinet.
Depending on the model they can be divided into two groups, in this case they are identified by diameter as external or internal.
The electric heating system is based on:
-electrical heating elements for the cooking cabinet and boiler, which generate heat
-SSR solid-state relays, which manage the power supply to heating elements.
-SSR plug-in board that controls the SSR
Warning: To avoid damaging the resistances, the heating is activated at 100% power only if the speed is high (set between speeds 4 and 6); activates at 50% power if speed is low (set between 1 and 3).
The heating of the boiler is entrusted to resistances in groups of 3 or 6 elements which must always be immerged in the water.
For this reason there is a water level control system (see steam generator for details).
Warning: Each group of boiler resistors has a seat for the safety thermostat which must always be positioned in the upper element oriented upwards
Warning:
Since the third phase is not interrupted, the elements are always under voltage when C6 is active.
Do not touch the parts and connections under voltage.
Heating element Test
A digital multimeter and a insulation tester are required to evaluate the replacement of the heating element.
Each heating element has its own ohm value based on the power and supply voltage, we therefore recommend checking it, after electrically insolating all the element terminal connections from the rest of the system, with the multimeter in Ohm.
- if the value is about 0 ohm the h. element is in short (also check the resistance between terminals and ground that must be infinite)
- if the value is infinite then the h. element is open
- If the h. element measures a few ohms, depending on the power and voltage (R=V2/W), then it is functional
SOLID STATE RELAYS SSR
Each SSR has two channels; the channel A with the inputs A1+ A2- which, with a low DC voltage, control the power contact L1 T1 and channel B which with B1+ B2- controls the power contact L2 T2.
The Solid-State Relay, later called SSR, is a component based on semiconductor technology and allows you to replace the classic contactors by managing the power supply of heating elements without any mechanical contact
Each SSR is used to control a single heating system (3 elements connected in Delta or Star mode).
Warning:
Since the third phase is not interrupted, the h. elements are always under voltage when C6 is active.
Do not touch the parts and connections under voltage.
Being based on semiconductor technology, SSRs develop heat during switching and keeping them at the correct temperature is extremely important for reliability.
To ensure reliability, SSRs are mounted on a heatsink just above the air filter.
TEST SOLID STATE RELAYS
To test the operation of SSRs it is recommended to use a current clamp or a digital multimeter with the voltage and insulation category appropriate to the supply voltage.
Solid-state relays can fail in two ways:
-leaving the contact / channel closed and therefore always feeding the heating elements until the intervention of the safety thermostat
-leaving the contact/ channel open interrupting the heating.
Current verification
This type of verification is the fastest and safest because the risk of touch live parts is minimal.
a)With the unit on standby, measure the current on the line not cut by the SSR; the current must be 0 A
Activate, from functional test, heating by setting the maximum power; the current detected must be the maximum current indicated in the installation manual
Voltage verification
This type of check must be carried out with the multimeter set in VAC; check the voltage at the junction heads of the SSR, be careful not to touch parts under voltage.
Check the voltage at the heads of contacts L1 – T1 and L2 – T2.
Voltage verification
a)The voltage measured with the unit in stand-by must be the line voltage, example (400VAC)
b)The voltage, measured with the unit in operation and maximum heating, must be about 1.2VAC > 1,5VAC
Replacement
Solid-state relays are supplied already assembled on a heatsink, to ensure proper assembly on the heatsink; never remove SSRs from the heatsink so as not to compromise proper operation.
if they are disconnected from the heatsink, it is necessary to tighten the screws with a controlled torque of 2.5N/m
Plug-In SSR
The J1 connector controls the chamber heating by managing the SSR of the chamber heating elements, J2 controls the boiler heating by managing the related SSRs.
The SSR are controlled by the SSR Plug-in, in turn check from the relays card, with a direct current signal (12VDC)
The Plug-in manages SSRs based on a 1 sec. duty-cycle that is divided into parts. Each SSR is managed from 0% (no activation) up to 100% (maximum power).
It is therefore possible to manage both the chamber and the boiler at the same time by heating the chamber to 60% and the boiler to 40% without exceeding the maximum power and without pausing one of the two systems.