Contactor. RCD. Emergency shutdown
Additional protection for abnormal situations.
Recommended to build.
The proposed protection works independently and switches the equipment off in critical abnormal situations.
The main danger is a breakthrough of alcohol vapors. If for some reason any of the following happens:
- The triac fails (short circuit).
- The voltage regulator hangs or works incorrectly.
- The automation fails.
- The 12 V power supply fails.
- There is no cooling.
Then you must switch off the heating and stop the vapor release. The monitoring point is the TCA (atmospheric vent tube).
This applies if a contactor is used together with Samovar.
You will need a bimetallic thermostat KSD9700 NC (normally closed) with a trip temperature of 55-70°C. Preferably with an insulated body: ceramic or plastic.
How to build it:
The negative voltage from the 12 V power supply is fed to the Samovar board not directly but through the KSD9700, which is attached to the TCA. It is most convenient to do this through a two-pin connector on the Samovar enclosure and a wire of the required length.
How it works.
If an emergency occurs that Samovar cannot handle (lost communication with the regulator, a failed triac, etc.), vapor starts to break through the TCA. The thermostat heats up and breaks the circuit. Samovar switches off, the control relay releases the contactor, and the contactor in turn cuts the heating. The vapor release stops. If a water valve is used, it closes.
After some time the TCA cools down, the thermostat closes its contacts, and Samovar switches on. But all the other devices will not switch on without your command.
Of course, first find out why the shutdown happened.
And of course, when you connect Samovar to the column, if you forget to plug in the connector, Samovar will not switch on, because there is no voltage, which is equivalent to a failed power supply.
Diagram of possible contactor locations
Point 5. The contactor switches on and powers the regulator and, at the same time, the triac, which will pass voltage to the load on the regulator's command.
The contactor is switched on by the "Turn on heating" («Включить нагрев») command from Samovar.
Accordingly, the regulator needs some time to start, and only then does it receive the "Boost" («Разгон») command from Samovar and apply voltage to the load. This delay is set by the SAMOVAR_USE_POWER_START_TIME parameter (2000 ms by default; in the configurator it is "Regulator start delay, ms" («Задержка запуска регулятора, мс») on the "Regulator" («Регулятор») tab), and for SEM_AVR another 3 s are added to it. If the regulator does not respond within this time, Samovar switches the heating off with the message "Regulator command timeout" («Таймаут команды регулятора»).
Weigh all the pros and cons before installing the contactor at this point.
Point 6. Strongly not recommended. A contactor at this point essentially just switches the regulator off, and that is all. The regulator itself consumes next to nothing, and if you need to switch off only the regulator, you can fit a low-power switch.
With this connection, if the regulator hangs, the triac fails, and so on, the heating element will keep heating.
Points 7 and 8. When the main power is applied, the regulator switches on. It starts for as long as it needs. You can adjust it, set voltages, and so on. But nothing goes to the load, because the contactor breaks the power circuit to the triac. Only when Samovar gives the "Turn on heating" («Включить нагрев») command does the contactor close and voltage go through the triac to the load.
Point 9 - recommended for installation. With the contactor installed here and the triac closed, the heating element is completely de-energized.
Option 2
Instead of a contactor you can use an RCD (residual-current device), which also adds safety against voltage leakage to the unit's body.
Sensor S1 (normally closed KSD9700) is installed on the TCA.
How it works.
To switch everything on, Samovar included, press and hold the normally closed button S2. The switching on is done by the RCD itself. After voltage is applied, the 12 V power supply starts and powers the coil of relay Rel1. The relay contacts (NO) close and LED HL1 lights up. Button S1 can now be released. The guard is ready. If the LED is not lit and you release the button, the RCD trips.
Let us consider the possible situations:
- The operator forgot to connect sensor S1 – the relay does not switch on – the RCD trips
- The triac fails – vapor through the TCA – sensor S1 breaks the circuit – the relay is de-energized – the RCD trips
- Insufficient cooling – vapor through the TCA – sensor S1 breaks the circuit – the relay is de-energized – the RCD trips
- The 12 V power supply fails – the relay is de-energized – the RCD trips
- The automation and/or the regulator hangs – vapor through the TCA – sensor S1 breaks the circuit – the relay is de-energized – the RCD trips.
- A short power outage – when the power returns, the RCD trips.
Example of building the monitoring unit
The TCA monitoring line unit.
Materials: stainless steel tube 6 mm in diameter, copper tube 6.1 mm in diameter (assuming the 18B20 sensor has no sleeve; if it has a sleeve, the tube is not required), a KSD9700 sensor, heat-shrink tubing, silicone tubing.
Place the stainless steel tube next to the copper one (or next to the temperature sensor sleeve). Choose the tube length so that the stainless one is a couple of centimeters longer. Lay the KSD9700 sensor on top and wrap the whole assembly with heat-shrink tubing. Insert the 18B20 sensor, which is assigned in Samovar as the TCA sensor, into the copper tube. Just in case, seal one end of the copper tube with any sealant to keep liquid out
For rectification, connect the stainless steel tube into the break of the line from the dephlegmator TCA to the vapor condensate drain container. From experience, it is better about 30 cm from the TCA.
When distilling wash and running a wash column, connect the stainless steel tube directly to the product outlet spout. That is, the product flows through the tube and on into the receiving container. In addition, you also see the product temperature at the outlet as the TCA temperature.
Since you can adjust the temperature of the water leaving the condenser in real time, you can tune the pump to its optimal output.
You can skip the copper tube altogether and press a sleeveless sensor directly against the stainless steel tube, but then you will have to take care of sealing the sensor, and the thermal contact area for the KSD9700 will also be smaller.
For correct operation, the temperature at which Samovar switches the heating off based on the TCA sensor ("TCA emergency temperature, °C" («Аварийная температура ТСА, °C») on the "Temperatures" («Температуры») tab of the configurator; in Samovar_ini.h it is the line)
//Maximum TCA temperature at which the power is switched off
#define MAX_ACP_TEMP 75
must be set 5-10° below the KSD9700 trip temperature. The default value of 75° is above the thermostat threshold of 55-70°, so it must be lowered.
Then, when vapor breaks through, Samovar acts first and issues the shutdown command, and if it is not carried out, the contactor or RCD trips.
