I have been working on designing a circuit which can reliable control the on/off cycles of a 1000W (vacuum cleaner) Motor and a 1000W Cartridge heating element. It should be noted that the motor and heating element both have an separate circuit. The circuit is as follows:
It works as follows:
- The circuit is designed for 230V Mains
- A micro-controller (ATMega328) will detect the zero crossing of the grid and decide whether to turn the motor/ heating element on or off for the following period.
- If the triac must be fired, PD4 will be pulled to high, triggering the photo triac, which will trigger the BTA208S-800E Triac.
- The snubber networks consisting of the resistors/ capacitors are supposed to protect the Triacs from misfiring.
Though, there are a few unanswered questions I would like to ask: First, the motor causes a lot of noise on the grid, does the snubber filter this unwanted EMI or would it need separate filtering (what/how)?
In the datasheet of the BTA208S-800E I found that the thermal resistance from junction to ambient is: 75K/W. How do you calculate the amount of Watts dissipated in the Triac? I plan on using a copper ground plane as heat sink.
Most European wall outlets have 2 pins for the power and a separate for earth. Can I connect the earth wire to the enclosure where both the heating element and motor are placed in?
Last, I would like to detect if the motor is not malfunctioning (if it is, both the heating element and motor should be shut down). I was wondering if detecting this would be possible by monitoring the back EMF caused by the motor?